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This paper examines the softening behaviour of cold sprayed 7075 aluminum alloy after isothermal annealing. The as-received powder was deposited by a high-pressure cold spray device using heated nitrogen as propellant gas. To investigate the effects of post-deposition heat treatment, the excised samples were isochronally annealed in the temperature range of 200 to 400 °C. The feedstock powder and the free-standing coatings were initially characterized through various electron microscopy techniques (SEM, EDS, EBSD) and relevant microstructural features were determined. Mechanical properties of the as-sprayed and heat-treated samples were evaluated by quasi-static tensile and microhardness testing. It has been shown that extensive plastic deformation during cold spraying resulted in a dense coating with relatively low internal porosity. Specimens in an as-deposited state possessed a high level of strain hardening and exhibited a brittle rupture associated with intersplat cracking. When subjected to heat treatment, the cold spray deposits showed a general trend of microhardness reduction and progressive sintering of the microstructure with increasing annealing temperature. Furthermore, post-mortem observation revealed a gradual transition in fracture mechanism, manifested by improving material ductility and the occurrence of typical dimple morphology. The aspects responsible for the softening of the cold sprayed 7075 alloys are discussed further.

This paper examines the softening behaviour of cold sprayed 7075 aluminum alloy after isothermal annealing. The as-received powder was deposited by a high-pressure cold spray device using heated nitrogen as propellant gas. To investigate the effects of post-deposition heat treatment, the excised samples were isochronally annealed in the temperature range of 200 to 400 °C. The feedstock powder and the free-standing coatings were initially characterized through various electron microscopy techniques (SEM, EDS, EBSD) and relevant microstructural features were determined. Mechanical properties of the as-sprayed and heat-treated samples were evaluated by quasi-static tensile and microhardness testing. It has been shown that extensive plastic deformation during cold spraying resulted in a dense coating with relatively low internal porosity. Specimens in an as-deposited state possessed a high level of strain hardening and exhibited a brittle rupture associated with intersplat cracking. When subjected to heat treatment, the cold spray deposits showed a general trend of microhardness reduction and progressive sintering of the microstructure with increasing annealing temperature. Furthermore, post-mortem observation revealed a gradual transition in fracture mechanism, manifested by improving material ductility and the occurrence of typical dimple morphology. The aspects responsible for the softening of the cold sprayed 7075 alloys are discussed further.

This paper examines the softening behaviour of cold sprayed 7075 aluminum alloy after isothermal annealing. The as-received powder was deposited by a high-pressure cold spray device using heated nitrogen as propellant gas. To investigate the effects of post-deposition heat treatment, the excised samples were isochronally annealed in the temperature range of 200 to 400 °C. The feedstock powder and the free-standing coatings were initially characterized through various electron microscopy techniques (SEM, EDS, EBSD) and relevant microstructural features were determined. Mechanical properties of the as-sprayed and heat-treated samples were evaluated by quasi-static tensile and microhardness testing. It has been shown that extensive plastic deformation during cold spraying resulted in a dense coating with relatively low internal porosity. Specimens in an as-deposited state possessed a high level of strain hardening and exhibited a brittle rupture associated with intersplat cracking. When subjected to heat treatment, the cold spray deposits showed a general trend of microhardness reduction and progressive sintering of the microstructure with increasing annealing temperature. Furthermore, post-mortem observation revealed a gradual transition in fracture mechanism, manifested by improving material ductility and the occurrence of typical dimple morphology. The aspects responsible for the softening of the cold sprayed 7075 alloys are discussed further.

Optimization is widely utilized for various engineering problems, mostly with the ultimate aim of minimizing the effort and required cost and/or maximizing the desired benefit. However, not all optimization problems can be effectively tackled using a single method, and problem-specific schemes need to be applied. In this dissertation, the central objective is to employ computational methods and propose/apply optimization techniques to achieve optimal solutions for the state-of-the-art problems in structural engineering and material processes, including energy storage, topology design, and cold spray additive manufacturing. Regarding energy storage, design optimization of compressed air energy storage using filament wound carbon fiber reinforced plastic pressure vessels is proposed and carried out to attain the most cost-effective option. As for topology design, a novel partition and microstructure-based method for topology optimization of large-scale structures is presented to maximize any metric, and, here, in particular, mechanical stiffness. Eventually, the most influential process variables for achieving high-quality cold spray depositions are identified and optimized by means of computational simulation of cold spray process and employment of machine learning algorithms.

Aluminum-based metal matrix composites (Al-MMCs) have shown enhanced strength, hardness, and wear properties. Hence, Al-MMCs are gaining momentum in the aerospace, automotive, defense and marine industries as a protective wear layer and for battlefield repairs. Recently, Al-MMC coatings were fabricated through cold spray (CS), a form of additive manufacturing (AM). The CS process has shown advantages of minimal oxidation, no phase transformation, and good metallurgical bonding when applied to a substrate. However, drawbacks such as porosity and low ductility limits its practical application. Heat treatments to CS coatings were successful in overcoming the drawbacks but sacrificed hardness for ductility. In a recent study, four variations of Al-MMCs CS coatings were fabricated using nano-sized aluminum and dual ceramic nanoparticle (NP) reinforcements, where the CS feedstock was synthesized through cryo-milling and high-energy ball milling. The study showed that the use of ceramic reinforcements of nano-boron carbide and boron nitride nanoplatelets at various combinations up to 2 vol% showed improvements in the hardness of the coating. Further research into controlling the properties of NP-reinforced Al-MMC CS coatings can further its application. This study examines the effect of heat treatments and the addition of up to two ceramic nanoparticles on the mechanical and tribological properties of an Al-MMCs coating fabricated by CS., Office of Naval Research, Major, Singapore Army, Approved for public release. Distribution is unlimited.

Cold spray technology has the potential to greatly reduce the effects of corrosion on susceptible materials. Lack of adhesion strength is one of the limitations currently preventing cold spray from becoming a dominant resource. Adhesion strength is the strength of the bond between the cold-sprayed coating and the substrate. Without good adhesion, the coating provides minimal protection against corrosion and could potentially make corrosion worse. In order to determine how to increase cold spray adhesion, the feedstock powder and substrate were manipulated to analyze their effects on adhesion. The main areas of focus for this project were the effects of the following characteristics on adhesion strength: i) the surface condition of the substrate, ii) the hardness of the substrate, and iii) the size of the cold spray particles. Samples within each area of focus were sprayed using cold spray and then a pull-off adhesion test was performed. The surface condition of the substrate was further studied to determine its effect on Mg AZ31 alloy’s corrosion rate by placing a smooth, roughened, and polished sample within a salt fog chamber for 672 hrs. The results from the adhesion tests showed that softer substrates and smoother surface condition produce higher adhesive strength. The corrosion experiments found that the samples with the higher roughness value saw the highest corrosion rates and formed the thickest oxide layer., Outstanding Thesis, Lieutenant, United States Navy, Approved for public release. distribution is unlimited

The selection of materials in the cold spraying process has a significant impact in corrosion resistance. Recognition of this could provide the opportunity to adapt a wide range of coating deposits for different applications for repair in protection against corrosion. Cold sprayed coatings of pure aluminum and alumina reinforced aluminum were deposited to understand the role of composition on corrosion. Coatings were sprayed with thicknesses varying from 100 µm to ~3 mm in order to understand the role of coating thickness on corrosion. A salt fog chamber test helps mimic an austere marine condition for 1000 hours and 2000 hours of continuous exposure. Dimensional changes and mass gain were measured periodically throughout the salt fog exposure testing. The corrosion test revealed that reinforced aluminum is better for protection than pure aluminum having unresolved galvanic vulnerabilities within the coating and delaminating from the substrate. The alumina reinforced coating exhibited greater roughness in thicker coatings, which resulted in higher initial corrosion rates. With additional testing, cold spray could be used for coating protection of parts that are exposed to austere environments., Lieutenant, United States Navy, Approved for public release. Distribution is unlimited.

Cold spray is a developing additive-manufacturing technology well suited as a preventive and corrective measure for metallic materials. The key challenge lies in formulating the optimal multifaceted spray parameters to achieve a functional coating on a substrate. Copper-nickel (Cu-Ni) alloy is particularly suited for study, due to its feasibility as both coating and repair material to be deposited onto a substrate through cold spray technology and its well-established characteristics for corrosion protection and mechanical strength. This thesis studied the change in mechanical behavior due to annealing of cold-sprayed Cu-Ni coating. In order to do so, the subject Cu-Ni powder's behavior and coating quality were characterized through the variation of certain spray parameters and examined by the mechanical behavior of multiple passes of Cu-Ni coatings through tensile testing, adhesion testing and nanoindentation testing. The as-sprayed coating exhibited brittleness and had weak mechanical interlocking adhesion with the substrate. Annealing mitigates and delays the mechanical deficiencies associated with porosity in the coating, which showed signs of the stronger metallurgical bonding with the substrate. Annealed cold spray coating itself can bear significant load and strengthen the substrate. Thus, cold spray coating with appropriate post-processing treatment can potentially reinforce and even repair the component to achieve robust mechanical behavior., Outstanding Thesis, Military Expert 5, Republic of Singapore Air Force, Approved for public release. Distribution is unlimited.

Bridge girder ends were the major weak points against corrosion. Therefore, it is necessary to develop the anticorrosion technique for them. In this study, we focused on Cold Spray technique, which can form a metallic film, as a corrosion protection film-forming method. In this study, we applied the mixed particles of zinc particles and alumina particles to the corroded steel bridge girder ends in the Cold Spray method to verify the corrosion protection performance and field applicability. Cold Spray Corrosion protection technology was applied to the corroded steel bridge girder ends, and corrosion monitoring was performed to verify the effectiveness in a corrosive environment.

Next generation nuclear reactor concepts employ higher temperatures, harder neutron fluxes, and generally a more difficult material environment than the current fleet. This, in conjunction with economic demands for longer periods between outages and higher fuel utilization, require radiation-hardened materials capable of withstanding such conditions. Oxide dispersion strengthened (ODS) steel alloys are one such potential class of materials. These are induced to have nanostructures within their bulk which provide distinct advan- tages, but which also preclude the use of consolidation and joining techniques which would degrade or destroy the same features. Cold spraying is an additive technique which has been explored as a possible avenue toward efficiently creating bulk parts out of ODS-precursor feedstock, with superior efficiency and properties compared to other means of consolidation, most commonly hot extrusion.This work has assessed the mechanical properties of one very promising ODS alloy, 14YWT, as formed by the cold spray technique. Results were not promising: the samples were brittle and weak, while not completely free of some of the disadvantages of hot extru- sion. Additionally, the demands of the cold-spray process were determined to be distinctly limiting as to the formation of the feedstock material, with negative impacts on the quality of the nanostructuring that forms the unique and desirable feature of the alloy. Though additional material processing and quality control may be able to remediate some of these defects, this work concludes that cold spraying is not a suitable mechanism for consolidating ODS alloys.

Niobium is used in superconducting radio frequency (SRF) structures that operate at cryogenictemperatures. These structures are continually optimized to increase efficiency and provide cost effectivefabrication. Throughout optimization, material properties of thermal conductivity and mechanical strengthare often jeopardized. Cold spraying has been of interest in coatings, repair, and additive manufacturingand poses a possible solution to optimization of SRF structures. This process involves deposition of adesired material onto a substrate through accelerating the material in the form of a powder to highvelocities via pressurized gas. Currently, the combination of copper powder being deposited onto a niobiumsubstrate via this process has never been studied. This is the first known study of cold-sprayed coppercoatings onto niobium for the application of conductive cooling of SRF accelerating structures. Trials wereconducted to assess the compatibility of cold spray of copper with SRF structures through processing andoperating conditions. The material campaign involved understanding parameters for sample fabrication,substrate preparation, material deposition, and post-processing that may provide optimal coatings. Thisstudy offers a firm base understanding of the copper and niobium cold spray pair. Effective deposition ofthis pair requires mechanical interlocking as there is no metallurgical bonding of these materials at theprocessing temperatures. The extent of mechanical interlocking is affected by substrate preparation andsurface roughness, oxygen content of copper powder, particle velocity, gas temperature, powdermorphology, and particle size distribution.

The cold spray technique was employed in this study to produce pure nickel (Ni) and nickel-Inconel 718 powder deposits on duplex stainless steel substrates. High quality coatings were manufactured using nitrogen as the propellant gas. The coatings exhibited satisfactory Inconel 718 (In718) retention within the Ni matrix due to the highly ductile binder phase necessary for fabrication. The characterization of the coating microstructures was implemented by means of X-ray diffraction, electron microscopy, energy-dispersive X-ray spectroscopy, and microhardness testing. In addition, the erosion resistance of both coatings was evaluated by performing cavitation erosion tests, with the analysis of the eroded surfaces revealing different erosion mechanisms for each coating. The results demonstrated the efficiency of the cold spray technique for use in the production of metal-metal matrix composite coatings and the potential of In718 use in applications which demand enhanced cavitation erosion resistance.

The cold spray technique was employed in this study to produce pure nickel (Ni) and nickel-Inconel 718 powder deposits on duplex stainless steel substrates. High quality coatings were manufactured using nitrogen as the propellant gas. The coatings exhibited satisfactory Inconel 718 (In718) retention within the Ni matrix due to the highly ductile binder phase necessary for fabrication. The characterization of the coating microstructures was implemented by means of X-ray diffraction, electron microscopy, energy-dispersive X-ray spectroscopy, and microhardness testing. In addition, the erosion resistance of both coatings was evaluated by performing cavitation erosion tests, with the analysis of the eroded surfaces revealing different erosion mechanisms for each coating. The results demonstrated the efficiency of the cold spray technique for use in the production of metal-metal matrix composite coatings and the potential of In718 use in applications which demand enhanced cavitation erosion resistance.

The cold spray technique was employed in this study to produce pure nickel (Ni) and nickel-Inconel 718 powder deposits on duplex stainless steel substrates. High quality coatings were manufactured using nitrogen as the propellant gas. The coatings exhibited satisfactory Inconel 718 (In718) retention within the Ni matrix due to the highly ductile binder phase necessary for fabrication. The characterization of the coating microstructures was implemented by means of X-ray diffraction, electron microscopy, energy-dispersive X-ray spectroscopy, and microhardness testing. In addition, the erosion resistance of both coatings was evaluated by performing cavitation erosion tests, with the analysis of the eroded surfaces revealing different erosion mechanisms for each coating. The results demonstrated the efficiency of the cold spray technique for use in the production of metal-metal matrix composite coatings and the potential of In718 use in applications which demand enhanced cavitation erosion resistance.

Niobium is used in superconducting radio frequency (SRF) structures that operate at cryogenictemperatures. These structures are continually optimized to increase efficiency and provide cost effectivefabrication. Throughout optimization, material properties of thermal conductivity and mechanical strengthare often jeopardized. Cold spraying has been of interest in coatings, repair, and additive manufacturingand poses a possible solution to optimization of SRF structures. This process involves deposition of adesired material onto a substrate through accelerating the material in the form of a powder to highvelocities via pressurized gas. Currently, the combination of copper powder being deposited onto a niobiumsubstrate via this process has never been studied. This is the first known study of cold-sprayed coppercoatings onto niobium for the application of conductive cooling of SRF accelerating structures. Trials wereconducted to assess the compatibility of cold spray of copper with SRF structures through processing andoperating conditions. The material campaign involved understanding parameters for sample fabrication,substrate preparation, material deposition, and post-processing that may provide optimal coatings. Thisstudy offers a firm base understanding of the copper and niobium cold spray pair. Effective deposition ofthis pair requires mechanical interlocking as there is no metallurgical bonding of these materials at theprocessing temperatures. The extent of mechanical interlocking is affected by substrate preparation andsurface roughness, oxygen content of copper powder, particle velocity, gas temperature, powdermorphology, and particle size distribution.

Next generation nuclear reactor concepts employ higher temperatures, harder neutron fluxes, and generally a more difficult material environment than the current fleet. This, in conjunction with economic demands for longer periods between outages and higher fuel utilization, require radiation-hardened materials capable of withstanding such conditions. Oxide dispersion strengthened (ODS) steel alloys are one such potential class of materials. These are induced to have nanostructures within their bulk which provide distinct advan- tages, but which also preclude the use of consolidation and joining techniques which would degrade or destroy the same features. Cold spraying is an additive technique which has been explored as a possible avenue toward efficiently creating bulk parts out of ODS-precursor feedstock, with superior efficiency and properties compared to other means of consolidation, most commonly hot extrusion.This work has assessed the mechanical properties of one very promising ODS alloy, 14YWT, as formed by the cold spray technique. Results were not promising: the samples were brittle and weak, while not completely free of some of the disadvantages of hot extru- sion. Additionally, the demands of the cold-spray process were determined to be distinctly limiting as to the formation of the feedstock material, with negative impacts on the quality of the nanostructuring that forms the unique and desirable feature of the alloy. Though additional material processing and quality control may be able to remediate some of these defects, this work concludes that cold spraying is not a suitable mechanism for consolidating ODS alloys.

As a form of additive manufacturing, the use of cold spray has made significant strides since different-sized particles were explored in the process. There is proof that micron-sized particles down to nanoparticles enhance the mechanical material properties of a substrate in wear resistance. Micron- and submicron-sized particles are beneficial, but due to their low relative surface areas, they tend to exhibit pull out more often and do not adhere to a substrate as well as a nanoparticle. Using nanoparticle metal and dual ceramic matrix reinforcements, six composites were fabricated through cryomilling and then applied to an aluminum substrate as a cold sprayed coating. Using nano-boron carbide (nB4C) and boron nitride nanoplatelets (BNNP) at various combinations up to 2 vol%, an increase of 11.59% in hardness from the control was achieved. Wear testing of each coating was performed, but most of the tests drove through the coatings into the substrate, indicating more refinement of the testing parameters is required. Additionally, corrosion testing was performed on cold sprayed samples for 500- and 2,000-hr trials in a salt fog chamber, revealing underlying pitting corrosion and galvanic corrosion vulnerabilities of the coatings. In the right application, the U.S. Navy could potentially use these coating materials in parts that are subjected to austere marine environments., Outstanding Thesis, Lieutenant, United States Navy, Approved for public release. distribution is unlimited

The cold spray technique was employed in this study to produce pure nickel (Ni) and nickel-Inconel 718 powder deposits on duplex stainless steel substrates. High quality coatings were manufactured using nitrogen as the propellant gas. The coatings exhibited satisfactory Inconel 718 (In718) retention within the Ni matrix due to the highly ductile binder phase necessary for fabrication. The characterization of the coating microstructures was implemented by means of X-ray diffraction, electron microscopy, energy-dispersive X-ray spectroscopy, and microhardness testing. In addition, the erosion resistance of both coatings was evaluated by performing cavitation erosion tests, with the analysis of the eroded surfaces revealing different erosion mechanisms for each coating. The results demonstrated the efficiency of the cold spray technique for use in the production of metal-metal matrix composite coatings and the potential of In718 use in applications which demand enhanced cavitation erosion resistance.

The cold spray technique was employed in this study to produce pure nickel (Ni) and nickel-Inconel 718 powder deposits on duplex stainless steel substrates. High quality coatings were manufactured using nitrogen as the propellant gas. The coatings exhibited satisfactory Inconel 718 (In718) retention within the Ni matrix due to the highly ductile binder phase necessary for fabrication. The characterization of the coating microstructures was implemented by means of X-ray diffraction, electron microscopy, energy-dispersive X-ray spectroscopy, and microhardness testing. In addition, the erosion resistance of both coatings was evaluated by performing cavitation erosion tests, with the analysis of the eroded surfaces revealing different erosion mechanisms for each coating. The results demonstrated the efficiency of the cold spray technique for use in the production of metal-metal matrix composite coatings and the potential of In718 use in applications which demand enhanced cavitation erosion resistance.

The cold spray technique was employed in this study to produce pure nickel (Ni) and nickel-Inconel 718 powder deposits on duplex stainless steel substrates. High quality coatings were manufactured using nitrogen as the propellant gas. The coatings exhibited satisfactory Inconel 718 (In718) retention within the Ni matrix due to the highly ductile binder phase necessary for fabrication. The characterization of the coating microstructures was implemented by means of X-ray diffraction, electron microscopy, energy-dispersive X-ray spectroscopy, and microhardness testing. In addition, the erosion resistance of both coatings was evaluated by performing cavitation erosion tests, with the analysis of the eroded surfaces revealing different erosion mechanisms for each coating. The results demonstrated the efficiency of the cold spray technique for use in the production of metal-metal matrix composite coatings and the potential of In718 use in applications which demand enhanced cavitation erosion resistance.

This article deals with the understanding of building-up mechanisms of bioactive nanocrystalline hydroxyapatite coatings by Cold Spray, revealing very promising results in contrast to more conventional techniques such as Plasma Spray. A full characterization of feedstock and coatings is provided. The agglomerated structure of the powder proved to be suitable to obtain successfully thick hydroxyapatite coatings. A crystallite size below similar to 20 nm in the powder and the as-sprayed coatings is calculated by the Rietveld X-ray refinement method and agreed by Transmission Electron Microscopy. Some wipe tests were carried out on Ti6Al4V substrates in order to study the deposition of single particles and the nanoscale features were evaluated. The resulting structure indicates that there is no delimitation of particle boundaries and the overall coating has been formed by effective compaction of the original nanocrystallites, leading to consistent and consolidated layers. (C) 2016 Elsevier Ltd. All rights reserved.

The cold spray technique has a great potential to deposit refractory metals for a variety of potential applications. Cold spraying of different metals have been addressed comprehensively to understand the deposition characteristics of the coatings. Since there is no available data on the deposition characteristics of cold sprayed Niobium, impact behavior of splats at different deposition conditions were simulated and numerically analyzed using Finite Element Modeling (FEM) and correlated with the experimental observations that highlight the role of the velocity and temperature of the particle upon impact on the bonding features. The increase in temperature of the splat drastically reduces the flow stress at the interface leading to best inter-splat bonding state. The synergistic effect of the temperature and the velocity leads to the formation of very dense, defect free niobium coating associated with deformation localization including interface melting. Formation of nanocrystalline grains at the inter-splat boundary was confirmed through TEM and compared with the FEM findings. Finally, understanding the deformation and deposition behavior of refractory metal such as niobium will be helpful to engineer the coatings for potential applications.

Deposition of metal matrix composites (MMCs) through thermal spraying has traditionally presented problems associated with heterogeneity, porosity, and low wettability of particulates with matrix. Cold spray is a very rapid deposition process which is suitable for depositing a variety of ductile materials without any thermal degradation. Many researchers have attempted to deposit Al-SiC MMCs with 10–20% SiC using this technique. In the present study, three different powder compositions (FAl-23SiC, FAl-46SiC, FAl-71SiC) obtained by mixing Al and SiC powders were cold sprayed on aluminum substrates. The volume percentage and the average size of the SiC particulates in the cold sprayed coatings were estimated and found to be 23%, 47% and 52% for FAl-23SiC, FAl-46SiC and FAl-71SiC feedstocks, respectively. Effects of percentage and size of the SiC particulate retained in the composite coatings on the mechanical properties and the sliding wear performance were studied at different sliding conditions in the as-sprayed and heat treated conditions. The results were comprehensively analyzed and found to correlate well with the microstructure of the coatings.

This paper presents a comparative study on Ti2AlC coatings produced by different thermal spray methods, as Ti2AlC is one of the most studied materials from the MAX phase family. Microstructural analysis on coatings produced by High Velocity Air Fuel (HVAF), Cold Spray and High Velocity Oxygen Fuel (HVOF) has been carried out by means of scanning electron microscopy equipped with energy dispersive spectrometer (EDS). The volume fraction of porosity was determined using the ASTM standard E562. The phase characterization of the as-received powder and the as-sprayed coatings was conducted using X-ray diffraction with Cr Kα radiation. Impact of spray parameters on the porosity and the mechanical properties of the coatings are also discussed. The results show that the spraying temperature and velocity plays a crucial role on coatings characteristics.

Numerical simulations of gas/particle flows of cold spray are performed for N2 and He, respectively, to investigate the usefulness of the two material-independent combination parameters derived from the equations of particle motion and temperature. The first combination parameter is the particle-diameter multiplied by the material density, which governs the particle velocity. The second one is the squared particle-diameter multiplied by the material density and specific heat, which affects the particle temperature.In the numerical simulation, the materials of the spray particle selected are WC-12Co, Cu and Ti. The numerical results show that the maximum impact velocity of particle is obtained, when the first combination parameter takes specific value regardless of the material type. Furthermore, it is shown that the particle diameter and its temperature corresponding to the maximum impact velocity can be graphically estimated by using the two combination parameters for any powder-materials normally used for the thermal spray.

In the present study, thick and dense niobium coatings were obtained using cold spray technique by using air as a process gas. Inter-splat boundaries are completely removed in the coatings heat treated at 1500 °C by the formation of equiaxed grains. Heat treatment reduces the porosity level to 0.1%. Inter-splat boundary bonding state of the heat treated coatings was investigated using micro-tensile testing, scratch testing and nanoindentation and compared with the bulk niobium. The elastic modulus of the cold spray coatings heat treated at 1500 °C exhibits as high as 103 GPa whereas the same for bulk is 105 GPa. The increase in mechanical strength of inter-splat boundary from as-sprayed condition to 1500 °C was estimated to be 750%. Similarly corrosion performance of heat treated coatings was also evaluated in 1 M KOH solution through potentiodynamic polarization as well as impedance spectroscopy studies. The corrosion rate for the coatings heat treated at 1500 °C was estimated to be 0.443 MPY which is comparable for the bulk (0.498 MPY). Coatings annealed at 1250 °C and above, which is very close to the recrystallization temperature of niobium, were found to perform almost as bulk niobium indicating exciting implications for various applications. Assessment of structure–property correlations was done based on the microstructure, porosity and inter-splat bonding state, together with the mechanical and corrosion properties of the heat treated tantalum cold sprayed coatings.

The cold-spray technique is of significant interest to deposit refractory metals with relatively high melting point for a variety of demanding applications. In the present study, mechanical properties of cold-sprayed tantalum coatings heat treated at different temperatures were investigated using microtensile testing, scratch testing, and nanoindentation. The corrosion performance of heat-treated coatings was also evaluated in 1 M KOH solution, and potentiodynamic polarization as well as impedance spectroscopy studies were carried out. Assessment of structure–property correlations was attempted based on microstructure, porosity, and intersplat bonding state, together with mechanical and corrosion properties of the heat-treated cold-sprayed tantalum coatings. Coatings annealed at 1500 °C, which is very close to the recrystallization temperature of tantalum, were found to perform almost as bulk tantalum, with exciting implications for various applications., This article is an invited paper selected from presentations at the 6th Asian Thermal Spray Conference (ATSC 2014) and has been expanded from the original presentation. ATSC 2014 was held in Hyderabad, India, November 24-26, 2014, and was organized by the International Advanced Research Centre for Powder Metallurgy and New Materials (ARCI) and the Asian Thermal Spray Society.

Titanium powder was deposited onto steel specimens using four thermal spray technologies: plasma spray, low-pressure cold spray, portable cold spray, and warm spray. The specimens were then subjected to strain controlled cyclic bending test in a dedicated in-house built device. The crack propagation was monitored by observing the changes in the resonance frequency of the samples. For each series, the number of cycles corresponding to a pre-defined specimen cross-section damage was used as a performance indicator. It was found that the grit-blasting procedure did not alter the fatigue properties of the steel specimens (1% increase as compared to as-received set), while the deposition of coatings via all four thermal spray technologies significantly increased the measured fatigue lives. The three high-velocity technologies led to relative lives increase of 234% (low-pressure cold spray), 210% (portable cold spray), and 355% (warm spray) and the deposition using plasma spray led to an increase of relative lives to 303%. The observed increase of high-velocity technologies (cold and warm spray) could be attributed to a combination of homogeneous fatigue resistant coatings and induction of peening stresses into the substrates via the impingement of the high-kinetic energy particles. Given the intrinsic character of the plasma jet (low-velocity impact of semi/molten particles) and the mostly ceramic character of the coating (oxides, nitrides), a hypothesis based on non-linear coatings behavior is provided in the paper., Titanový prášek komerční čistoty byl nanesen na ocelové substráty pomocí čtyř technologií: plazmovým nanášením, nízkotlakým a přenosným studeným kinetickým nanášením a středně-teplotním nanášením. Vzorky byly posléze podrobeny únavovému testování cyklickým ohybem s kontrolovanou výchylkou volného konce na vlastnoručně sestaveném zařízení. Pomocí změn v rezonanční frekvenci těles byl sledován průběh šíření trhlin. Počet cyklů při dosažení stanoveného porušení průřezu vzorku byl hodnocen jako ukazatel únavové odolnosti. Bylo zjištěno, že u ocelových substrátů nemá otryskání povrchu významný vliv na únavovou životnost vzorků (zvýšení pouze 1%), zatímco nanesení nástřiků všemi technologiemi způsobilo její významný nárůst. Tři vysokorychlostní technologie vedly ke zvýšení životnosti o 234% (nízkotlaké kinetické nanášení), 210% (přenosné kinetické nanášení) a 355% (středně-teplotní nanášení) a depozice za použití plazmového nanášení vedla ke zvýšení relativní životnosti o 303%. Nárůst životnosti u vysokorychlostních metod (studené a středně-teplotní nanášení) je pravděpodobně způsoben přítomností relativně homogenních únavově odolných vrstev a též vznikem kompresivních napětí v substrátech dopadem vysokoenergetických částic. Vzhledem k typickému charakteru vrstev nanesených plazmovým hořákem (tj. nízkorychlostní dopad částečně nebo zcela natavených částic) a jejich převážně keramickému charakteru (oxidy, nitridy), je v článku navrženo vysvětlení založené na nelineárním chování nástřiků.

Four blends of Al powder containing different amounts of Ti were deposited onto Ti-46Al-7Nb substrates as oxidation-protection layers using low-pressure cold spray. The coating morphology and chemical composition were assessed. Optimized heat treatment in protective atmosphere was carried out in order to induce formation of intermetallic phases within the deposits. The specimens were then subjected to 950'C exposure for 100, 250, and 500 hrs and their oxidation performance was monitored using the gravimetric method. It was found that the oxidation rate of the coating-protected specimens was substantially reduced (an increase in the weight gain of 1.37 mg/cm2 after 500 hrs of specimen with Al coating) as compared to their uncoated counterparts (1.21 mg/cm2 after 50 hrs at 900'C). The oxidation rates increased with increasing content of Ti in the coatings. Substantial changes of the coating integrity were recorded after the long-term oxidation testing., V rámci této studie byly na substráty slitiny Ti-46Al-7Nb pomocí nízkotlaké technologie kinetického nanášení deponovány čtyři antikorozní vrstvy Al obsahující různá množství Ti. Byla stanovena morfologie a chemické složení vzniklých nástřiků a posléze bylo provedeno optimalizované žíhání vzorků v ochranné atmosféře s cílem tvorby intermetalických fází v nástřicích. Hlavní část studie byla poté dlouhodobá tepelná zátěžová zkouška při 950'C (trvání 100, 250 a 500 hodin), při které byla sledována oxidační odolnost gravimetrickou metodou. Bylo zjištěno, že u depozicí vrstev došlo u vzorků k významnému snížení rychlosti oxidace (nárůst hmotnosti 1.37 mg/cm2 po 500 hod u vzorků s nástřikem Al) ve srovnání s původními, nepovlakovanými vzorky (1.21 mg/cm2 po pouhých 50 hod při 900'C). Rychlost oxidace se se zvyšujícím se obsahem Ti zrychlovala. Po tomto zatěžování rovněž došlo k zásadnímu porušení integrity nástřiků.

Four blends of Al powder containing different amounts of Ti were deposited onto Ti-46Al-7Nb substrates as oxidation-protection layers using low-pressure cold spray. The coating morphology and chemical composition were assessed. Optimized heat treatment in protective atmosphere was carried out in order to induce formation of intermetallic phases within the deposits. The specimens were then subjected to 950'C exposure for 100, 250, and 500 hrs and their oxidation performance was monitored using the gravimetric method. It was found that the oxidation rate of the coating-protected specimens was substantially reduced (an increase in the weight gain of 1.37 mg/cm2 after 500 hrs of specimen with Al coating) as compared to their uncoated counterparts (1.21 mg/cm2 after 50 hrs at 900'C). The oxidation rates increased with increasing content of Ti in the coatings. Substantial changes of the coating integrity were recorded after the long-term oxidation testing., V rámci této studie byly na substráty slitiny Ti-46Al-7Nb pomocí nízkotlaké technologie kinetického nanášení deponovány čtyři antikorozní vrstvy Al obsahující různá množství Ti. Byla stanovena morfologie a chemické složení vzniklých nástřiků a posléze bylo provedeno optimalizované žíhání vzorků v ochranné atmosféře s cílem tvorby intermetalických fází v nástřicích. Hlavní část studie byla poté dlouhodobá tepelná zátěžová zkouška při 950'C (trvání 100, 250 a 500 hodin), při které byla sledována oxidační odolnost gravimetrickou metodou. Bylo zjištěno, že u depozicí vrstev došlo u vzorků k významnému snížení rychlosti oxidace (nárůst hmotnosti 1.37 mg/cm2 po 500 hod u vzorků s nástřikem Al) ve srovnání s původními, nepovlakovanými vzorky (1.21 mg/cm2 po pouhých 50 hod při 900'C). Rychlost oxidace se se zvyšujícím se obsahem Ti zrychlovala. Po tomto zatěžování rovněž došlo k zásadnímu porušení integrity nástřiků.

Titanium powder was deposited onto steel specimens using four thermal spray technologies: plasma spray, low-pressure cold spray, portable cold spray, and warm spray. The specimens were then subjected to strain controlled cyclic bending test in a dedicated in-house built device. The crack propagation was monitored by observing the changes in the resonance frequency of the samples. For each series, the number of cycles corresponding to a pre-defined specimen cross-section damage was used as a performance indicator. It was found that the grit-blasting procedure did not alter the fatigue properties of the steel specimens (1% increase as compared to as-received set), while the deposition of coatings via all four thermal spray technologies significantly increased the measured fatigue lives. The three high-velocity technologies led to relative lives increase of 234% (low-pressure cold spray), 210% (portable cold spray), and 355% (warm spray) and the deposition using plasma spray led to an increase of relative lives to 303%. The observed increase of high-velocity technologies (cold and warm spray) could be attributed to a combination of homogeneous fatigue resistant coatings and induction of peening stresses into the substrates via the impingement of the high-kinetic energy particles. Given the intrinsic character of the plasma jet (low-velocity impact of semi/molten particles) and the mostly ceramic character of the coating (oxides, nitrides), a hypothesis based on non-linear coatings behavior is provided in the paper., Titanový prášek komerční čistoty byl nanesen na ocelové substráty pomocí čtyř technologií: plazmovým nanášením, nízkotlakým a přenosným studeným kinetickým nanášením a středně-teplotním nanášením. Vzorky byly posléze podrobeny únavovému testování cyklickým ohybem s kontrolovanou výchylkou volného konce na vlastnoručně sestaveném zařízení. Pomocí změn v rezonanční frekvenci těles byl sledován průběh šíření trhlin. Počet cyklů při dosažení stanoveného porušení průřezu vzorku byl hodnocen jako ukazatel únavové odolnosti. Bylo zjištěno, že u ocelových substrátů nemá otryskání povrchu významný vliv na únavovou životnost vzorků (zvýšení pouze 1%), zatímco nanesení nástřiků všemi technologiemi způsobilo její významný nárůst. Tři vysokorychlostní technologie vedly ke zvýšení životnosti o 234% (nízkotlaké kinetické nanášení), 210% (přenosné kinetické nanášení) a 355% (středně-teplotní nanášení) a depozice za použití plazmového nanášení vedla ke zvýšení relativní životnosti o 303%. Nárůst životnosti u vysokorychlostních metod (studené a středně-teplotní nanášení) je pravděpodobně způsoben přítomností relativně homogenních únavově odolných vrstev a též vznikem kompresivních napětí v substrátech dopadem vysokoenergetických částic. Vzhledem k typickému charakteru vrstev nanesených plazmovým hořákem (tj. nízkorychlostní dopad částečně nebo zcela natavených částic) a jejich převážně keramickému charakteru (oxidy, nitridy), je v článku navrženo vysvětlení založené na nelineárním chování nástřiků.

Titanium powder was deposited onto steel specimens using four thermal spray technologies: plasma spray, low-pressure cold spray, portable cold spray, and warm spray. The specimens were then subjected to strain controlled cyclic bending test in a dedicated in-house built device. The crack propagation was monitored by observing the changes in the resonance frequency of the samples. For each series, the number of cycles corresponding to a pre-defined specimen cross-section damage was used as a performance indicator. It was found that the grit-blasting procedure did not alter the fatigue properties of the steel specimens (1% increase as compared to as-received set), while the deposition of coatings via all four thermal spray technologies significantly increased the measured fatigue lives. The three high-velocity technologies led to relative lives increase of 234% (low-pressure cold spray), 210% (portable cold spray), and 355% (warm spray) and the deposition using plasma spray led to an increase of relative lives to 303%. The observed increase of high-velocity technologies (cold and warm spray) could be attributed to a combination of homogeneous fatigue resistant coatings and induction of peening stresses into the substrates via the impingement of the high-kinetic energy particles. Given the intrinsic character of the plasma jet (low-velocity impact of semi/molten particles) and the mostly ceramic character of the coating (oxides, nitrides), a hypothesis based on non-linear coatings behavior is provided in the paper., Titanový prášek komerční čistoty byl nanesen na ocelové substráty pomocí čtyř technologií: plazmovým nanášením, nízkotlakým a přenosným studeným kinetickým nanášením a středně-teplotním nanášením. Vzorky byly posléze podrobeny únavovému testování cyklickým ohybem s kontrolovanou výchylkou volného konce na vlastnoručně sestaveném zařízení. Pomocí změn v rezonanční frekvenci těles byl sledován průběh šíření trhlin. Počet cyklů při dosažení stanoveného porušení průřezu vzorku byl hodnocen jako ukazatel únavové odolnosti. Bylo zjištěno, že u ocelových substrátů nemá otryskání povrchu významný vliv na únavovou životnost vzorků (zvýšení pouze 1%), zatímco nanesení nástřiků všemi technologiemi způsobilo její významný nárůst. Tři vysokorychlostní technologie vedly ke zvýšení životnosti o 234% (nízkotlaké kinetické nanášení), 210% (přenosné kinetické nanášení) a 355% (středně-teplotní nanášení) a depozice za použití plazmového nanášení vedla ke zvýšení relativní životnosti o 303%. Nárůst životnosti u vysokorychlostních metod (studené a středně-teplotní nanášení) je pravděpodobně způsoben přítomností relativně homogenních únavově odolných vrstev a též vznikem kompresivních napětí v substrátech dopadem vysokoenergetických částic. Vzhledem k typickému charakteru vrstev nanesených plazmovým hořákem (tj. nízkorychlostní dopad částečně nebo zcela natavených částic) a jejich převážně keramickému charakteru (oxidy, nitridy), je v článku navrženo vysvětlení založené na nelineárním chování nástřiků.

Four blends of Al powder containing different amounts of Ti were deposited onto Ti-46Al-7Nb substrates as oxidation-protection layers using low-pressure cold spray. The coating morphology and chemical composition were assessed. Optimized heat treatment in protective atmosphere was carried out in order to induce formation of intermetallic phases within the deposits. The specimens were then subjected to 950'C exposure for 100, 250, and 500 hrs and their oxidation performance was monitored using the gravimetric method. It was found that the oxidation rate of the coating-protected specimens was substantially reduced (an increase in the weight gain of 1.37 mg/cm2 after 500 hrs of specimen with Al coating) as compared to their uncoated counterparts (1.21 mg/cm2 after 50 hrs at 900'C). The oxidation rates increased with increasing content of Ti in the coatings. Substantial changes of the coating integrity were recorded after the long-term oxidation testing., V rámci této studie byly na substráty slitiny Ti-46Al-7Nb pomocí nízkotlaké technologie kinetického nanášení deponovány čtyři antikorozní vrstvy Al obsahující různá množství Ti. Byla stanovena morfologie a chemické složení vzniklých nástřiků a posléze bylo provedeno optimalizované žíhání vzorků v ochranné atmosféře s cílem tvorby intermetalických fází v nástřicích. Hlavní část studie byla poté dlouhodobá tepelná zátěžová zkouška při 950'C (trvání 100, 250 a 500 hodin), při které byla sledována oxidační odolnost gravimetrickou metodou. Bylo zjištěno, že u depozicí vrstev došlo u vzorků k významnému snížení rychlosti oxidace (nárůst hmotnosti 1.37 mg/cm2 po 500 hod u vzorků s nástřikem Al) ve srovnání s původními, nepovlakovanými vzorky (1.21 mg/cm2 po pouhých 50 hod při 900'C). Rychlost oxidace se se zvyšujícím se obsahem Ti zrychlovala. Po tomto zatěžování rovněž došlo k zásadnímu porušení integrity nástřiků.

Titanium powder was deposited onto steel specimens using four thermal spray technologies: plasma spray, low-pressure cold spray, portable cold spray, and warm spray. The specimens were then subjected to strain controlled cyclic bending test in a dedicated in-house built device. The crack propagation was monitored by observing the changes in the resonance frequency of the samples. For each series, the number of cycles corresponding to a pre-defined specimen cross-section damage was used as a performance indicator. It was found that the grit-blasting procedure did not alter the fatigue properties of the steel specimens (1% increase as compared to as-received set), while the deposition of coatings via all four thermal spray technologies significantly increased the measured fatigue lives. The three high-velocity technologies led to relative lives increase of 234% (low-pressure cold spray), 210% (portable cold spray), and 355% (warm spray) and the deposition using plasma spray led to an increase of relative lives to 303%. The observed increase of high-velocity technologies (cold and warm spray) could be attributed to a combination of homogeneous fatigue resistant coatings and induction of peening stresses into the substrates via the impingement of the high-kinetic energy particles. Given the intrinsic character of the plasma jet (low-velocity impact of semi/molten particles) and the mostly ceramic character of the coating (oxides, nitrides), a hypothesis based on non-linear coatings behavior is provided in the paper., Titanový prášek komerční čistoty byl nanesen na ocelové substráty pomocí čtyř technologií: plazmovým nanášením, nízkotlakým a přenosným studeným kinetickým nanášením a středně-teplotním nanášením. Vzorky byly posléze podrobeny únavovému testování cyklickým ohybem s kontrolovanou výchylkou volného konce na vlastnoručně sestaveném zařízení. Pomocí změn v rezonanční frekvenci těles byl sledován průběh šíření trhlin. Počet cyklů při dosažení stanoveného porušení průřezu vzorku byl hodnocen jako ukazatel únavové odolnosti. Bylo zjištěno, že u ocelových substrátů nemá otryskání povrchu významný vliv na únavovou životnost vzorků (zvýšení pouze 1%), zatímco nanesení nástřiků všemi technologiemi způsobilo její významný nárůst. Tři vysokorychlostní technologie vedly ke zvýšení životnosti o 234% (nízkotlaké kinetické nanášení), 210% (přenosné kinetické nanášení) a 355% (středně-teplotní nanášení) a depozice za použití plazmového nanášení vedla ke zvýšení relativní životnosti o 303%. Nárůst životnosti u vysokorychlostních metod (studené a středně-teplotní nanášení) je pravděpodobně způsoben přítomností relativně homogenních únavově odolných vrstev a též vznikem kompresivních napětí v substrátech dopadem vysokoenergetických částic. Vzhledem k typickému charakteru vrstev nanesených plazmovým hořákem (tj. nízkorychlostní dopad částečně nebo zcela natavených částic) a jejich převážně keramickému charakteru (oxidy, nitridy), je v článku navrženo vysvětlení založené na nelineárním chování nástřiků.

Four blends of Al powder containing different amounts of Ti were deposited onto Ti-46Al-7Nb substrates as oxidation-protection layers using low-pressure cold spray. The coating morphology and chemical composition were assessed. Optimized heat treatment in protective atmosphere was carried out in order to induce formation of intermetallic phases within the deposits. The specimens were then subjected to 950'C exposure for 100, 250, and 500 hrs and their oxidation performance was monitored using the gravimetric method. It was found that the oxidation rate of the coating-protected specimens was substantially reduced (an increase in the weight gain of 1.37 mg/cm2 after 500 hrs of specimen with Al coating) as compared to their uncoated counterparts (1.21 mg/cm2 after 50 hrs at 900'C). The oxidation rates increased with increasing content of Ti in the coatings. Substantial changes of the coating integrity were recorded after the long-term oxidation testing., V rámci této studie byly na substráty slitiny Ti-46Al-7Nb pomocí nízkotlaké technologie kinetického nanášení deponovány čtyři antikorozní vrstvy Al obsahující různá množství Ti. Byla stanovena morfologie a chemické složení vzniklých nástřiků a posléze bylo provedeno optimalizované žíhání vzorků v ochranné atmosféře s cílem tvorby intermetalických fází v nástřicích. Hlavní část studie byla poté dlouhodobá tepelná zátěžová zkouška při 950'C (trvání 100, 250 a 500 hodin), při které byla sledována oxidační odolnost gravimetrickou metodou. Bylo zjištěno, že u depozicí vrstev došlo u vzorků k významnému snížení rychlosti oxidace (nárůst hmotnosti 1.37 mg/cm2 po 500 hod u vzorků s nástřikem Al) ve srovnání s původními, nepovlakovanými vzorky (1.21 mg/cm2 po pouhých 50 hod při 900'C). Rychlost oxidace se se zvyšujícím se obsahem Ti zrychlovala. Po tomto zatěžování rovněž došlo k zásadnímu porušení integrity nástřiků.

Four blends of Al powder containing different amounts of Ti were deposited onto Ti-46Al-7Nb substrates as oxidation-protection layers using low-pressure cold spray. The coating morphology and chemical composition were assessed. Optimized heat treatment in protective atmosphere was carried out in order to induce formation of intermetallic phases within the deposits. The specimens were then subjected to 950'C exposure for 100, 250, and 500 hrs and their oxidation performance was monitored using the gravimetric method. It was found that the oxidation rate of the coating-protected specimens was substantially reduced (an increase in the weight gain of 1.37 mg/cm2 after 500 hrs of specimen with Al coating) as compared to their uncoated counterparts (1.21 mg/cm2 after 50 hrs at 900'C). The oxidation rates increased with increasing content of Ti in the coatings. Substantial changes of the coating integrity were recorded after the long-term oxidation testing., V rámci této studie byly na substráty slitiny Ti-46Al-7Nb pomocí nízkotlaké technologie kinetického nanášení deponovány čtyři antikorozní vrstvy Al obsahující různá množství Ti. Byla stanovena morfologie a chemické složení vzniklých nástřiků a posléze bylo provedeno optimalizované žíhání vzorků v ochranné atmosféře s cílem tvorby intermetalických fází v nástřicích. Hlavní část studie byla poté dlouhodobá tepelná zátěžová zkouška při 950'C (trvání 100, 250 a 500 hodin), při které byla sledována oxidační odolnost gravimetrickou metodou. Bylo zjištěno, že u depozicí vrstev došlo u vzorků k významnému snížení rychlosti oxidace (nárůst hmotnosti 1.37 mg/cm2 po 500 hod u vzorků s nástřikem Al) ve srovnání s původními, nepovlakovanými vzorky (1.21 mg/cm2 po pouhých 50 hod při 900'C). Rychlost oxidace se se zvyšujícím se obsahem Ti zrychlovala. Po tomto zatěžování rovněž došlo k zásadnímu porušení integrity nástřiků.

Titanium powder was deposited onto steel specimens using four thermal spray technologies: plasma spray, low-pressure cold spray, portable cold spray, and warm spray. The specimens were then subjected to strain controlled cyclic bending test in a dedicated in-house built device. The crack propagation was monitored by observing the changes in the resonance frequency of the samples. For each series, the number of cycles corresponding to a pre-defined specimen cross-section damage was used as a performance indicator. It was found that the grit-blasting procedure did not alter the fatigue properties of the steel specimens (1% increase as compared to as-received set), while the deposition of coatings via all four thermal spray technologies significantly increased the measured fatigue lives. The three high-velocity technologies led to relative lives increase of 234% (low-pressure cold spray), 210% (portable cold spray), and 355% (warm spray) and the deposition using plasma spray led to an increase of relative lives to 303%. The observed increase of high-velocity technologies (cold and warm spray) could be attributed to a combination of homogeneous fatigue resistant coatings and induction of peening stresses into the substrates via the impingement of the high-kinetic energy particles. Given the intrinsic character of the plasma jet (low-velocity impact of semi/molten particles) and the mostly ceramic character of the coating (oxides, nitrides), a hypothesis based on non-linear coatings behavior is provided in the paper., Titanový prášek komerční čistoty byl nanesen na ocelové substráty pomocí čtyř technologií: plazmovým nanášením, nízkotlakým a přenosným studeným kinetickým nanášením a středně-teplotním nanášením. Vzorky byly posléze podrobeny únavovému testování cyklickým ohybem s kontrolovanou výchylkou volného konce na vlastnoručně sestaveném zařízení. Pomocí změn v rezonanční frekvenci těles byl sledován průběh šíření trhlin. Počet cyklů při dosažení stanoveného porušení průřezu vzorku byl hodnocen jako ukazatel únavové odolnosti. Bylo zjištěno, že u ocelových substrátů nemá otryskání povrchu významný vliv na únavovou životnost vzorků (zvýšení pouze 1%), zatímco nanesení nástřiků všemi technologiemi způsobilo její významný nárůst. Tři vysokorychlostní technologie vedly ke zvýšení životnosti o 234% (nízkotlaké kinetické nanášení), 210% (přenosné kinetické nanášení) a 355% (středně-teplotní nanášení) a depozice za použití plazmového nanášení vedla ke zvýšení relativní životnosti o 303%. Nárůst životnosti u vysokorychlostních metod (studené a středně-teplotní nanášení) je pravděpodobně způsoben přítomností relativně homogenních únavově odolných vrstev a též vznikem kompresivních napětí v substrátech dopadem vysokoenergetických částic. Vzhledem k typickému charakteru vrstev nanesených plazmovým hořákem (tj. nízkorychlostní dopad částečně nebo zcela natavených částic) a jejich převážně keramickému charakteru (oxidy, nitridy), je v článku navrženo vysvětlení založené na nelineárním chování nástřiků.

Four blends of Al powder containing different amounts of Ti were deposited onto Ti-46Al-7Nb substrates as oxidation-protection layers using low-pressure cold spray. The coating morphology and chemical composition were assessed. Optimized heat treatment in protective atmosphere was carried out in order to induce formation of intermetallic phases within the deposits. The specimens were then subjected to 950'C exposure for 100, 250, and 500 hrs and their oxidation performance was monitored using the gravimetric method. It was found that the oxidation rate of the coating-protected specimens was substantially reduced (an increase in the weight gain of 1.37 mg/cm2 after 500 hrs of specimen with Al coating) as compared to their uncoated counterparts (1.21 mg/cm2 after 50 hrs at 900'C). The oxidation rates increased with increasing content of Ti in the coatings. Substantial changes of the coating integrity were recorded after the long-term oxidation testing., V rámci této studie byly na substráty slitiny Ti-46Al-7Nb pomocí nízkotlaké technologie kinetického nanášení deponovány čtyři antikorozní vrstvy Al obsahující různá množství Ti. Byla stanovena morfologie a chemické složení vzniklých nástřiků a posléze bylo provedeno optimalizované žíhání vzorků v ochranné atmosféře s cílem tvorby intermetalických fází v nástřicích. Hlavní část studie byla poté dlouhodobá tepelná zátěžová zkouška při 950'C (trvání 100, 250 a 500 hodin), při které byla sledována oxidační odolnost gravimetrickou metodou. Bylo zjištěno, že u depozicí vrstev došlo u vzorků k významnému snížení rychlosti oxidace (nárůst hmotnosti 1.37 mg/cm2 po 500 hod u vzorků s nástřikem Al) ve srovnání s původními, nepovlakovanými vzorky (1.21 mg/cm2 po pouhých 50 hod při 900'C). Rychlost oxidace se se zvyšujícím se obsahem Ti zrychlovala. Po tomto zatěžování rovněž došlo k zásadnímu porušení integrity nástřiků.

This paper presents a summary of the research on the influence of plasma and cold spray deposition of bio-grade Ti powder on the high-cycle fatigue properties of Ti6Al4V substrates. Four sets of flat specimens (as-received, grit-blasted, plasma and cold sprayed) were prepared and subjected to cantilever–beam cyclic bend loading with a constant deflection of the free end. It was found that the grit-blasting procedure significantly increased the fatigue lives of the specimens compared to the as-received set (1.81x increase). The deposition of the coatings onto grit-blasted specimens led to deterioration of fatigue properties. The average fatigue lives of the plasma sprayed and cold sprayed samples reached 1.16x and 0.91x of the as-received specimens, respectively. In order to understand the positive effect of the grit-blasting procedure and the adverse effect of the coatings deposition on fatigue lives, chemical analyses, fractographic analysis, microstructural investigations as well as layers elastic moduli estimation were carried out. It was found that the cold spray deposition retained the composition of the powder feedstock while a complete transformation of Ti into nitrides and oxides was detected in the plasma deposited layers. Owing to the different coating build-up principles and their respective different porosity levels, the moduli of the coatings were found to vary (7.2 GPa for plasma sprayed and 36.7 GPa for cold sprayed layers). The fatigue crack initiation sites and propagation directions in the plasma and cold sprayed specimens were found to differ substantially. Based on the obtained results, two explanations of the fatigue loading results are suggested in the paper., Tento článek představuje shrnutí výsledků výzkumu vlivu plazmového a kinetického nanášení biologických vrstev Ti na únavové vlastnosti substrátů Ti6Al4V. Čtyři vyrobené série vzorků (původní, otryskané, s plazmově nanesenou vrstvou, s vrstvou nanesenou studenou kinetizací) byly vystaveny cyklickému ohybu s krakorcovým upnutím a konstantní výchylkou volného konce. Bylo zjištěno, že procedura tryskání významně prodlužuje únavové životy vzorků ve srovnání s původními tělesy (nárůst až 1.81x). Depozice vrstev na tyto tryskané povrchy vedla ke zhoršení únavových charakteristik. Průměrný únavový život vzorků s plazmově nanesenými vrstvami dosáhl 1.16x a vzorků s vrstvami nanesenými studenou kinetizací 0.91x hodnot původních netryskaných vzorků. Pro pochopení kladného efektu technologie tryskání a negativního efektu depozice nástřiků na únavové životy byla uskutečněna řada analýz (chemické, fraktografické, mikrostrukturální) a byly kalkulovány elastické moduly vrstev. Bylo zjištěno, že nástřik pomocí studené kinetizace nezměnil složení původního Ti prášku, kdežto u vrstev deponovaných plazmovým nanášením byla pozorována kompletní transformace na nitridy a oxidy. Vzhledem k rozdílným principům vzniku vrstev a jejich odlišné porozitě byly dále zjištěny zásadní rozdíly v jejich elastických modulech (7.2 GPa u plazmově a 36.7 GPa u kineticky nanesených vrstev). bylo prokázáno, že místa iniciací únavových trhlin a směry jejich šíření v plazmově a kineticky nanesených vrstvách se výrazně odlišují. Na základě získaných poznatků byly v textu navrženy dvě výklady výsledků únavového zatěžování.

This paper presents a summary of the research on the influence of plasma and cold spray deposition of bio-grade Ti powder on the high-cycle fatigue properties of Ti6Al4V substrates. Four sets of flat specimens (as-received, grit-blasted, plasma and cold sprayed) were prepared and subjected to cantilever–beam cyclic bend loading with a constant deflection of the free end. It was found that the grit-blasting procedure significantly increased the fatigue lives of the specimens compared to the as-received set (1.81x increase). The deposition of the coatings onto grit-blasted specimens led to deterioration of fatigue properties. The average fatigue lives of the plasma sprayed and cold sprayed samples reached 1.16x and 0.91x of the as-received specimens, respectively. In order to understand the positive effect of the grit-blasting procedure and the adverse effect of the coatings deposition on fatigue lives, chemical analyses, fractographic analysis, microstructural investigations as well as layers elastic moduli estimation were carried out. It was found that the cold spray deposition retained the composition of the powder feedstock while a complete transformation of Ti into nitrides and oxides was detected in the plasma deposited layers. Owing to the different coating build-up principles and their respective different porosity levels, the moduli of the coatings were found to vary (7.2 GPa for plasma sprayed and 36.7 GPa for cold sprayed layers). The fatigue crack initiation sites and propagation directions in the plasma and cold sprayed specimens were found to differ substantially. Based on the obtained results, two explanations of the fatigue loading results are suggested in the paper., Tento článek představuje shrnutí výsledků výzkumu vlivu plazmového a kinetického nanášení biologických vrstev Ti na únavové vlastnosti substrátů Ti6Al4V. Čtyři vyrobené série vzorků (původní, otryskané, s plazmově nanesenou vrstvou, s vrstvou nanesenou studenou kinetizací) byly vystaveny cyklickému ohybu s krakorcovým upnutím a konstantní výchylkou volného konce. Bylo zjištěno, že procedura tryskání významně prodlužuje únavové životy vzorků ve srovnání s původními tělesy (nárůst až 1.81x). Depozice vrstev na tyto tryskané povrchy vedla ke zhoršení únavových charakteristik. Průměrný únavový život vzorků s plazmově nanesenými vrstvami dosáhl 1.16x a vzorků s vrstvami nanesenými studenou kinetizací 0.91x hodnot původních netryskaných vzorků. Pro pochopení kladného efektu technologie tryskání a negativního efektu depozice nástřiků na únavové životy byla uskutečněna řada analýz (chemické, fraktografické, mikrostrukturální) a byly kalkulovány elastické moduly vrstev. Bylo zjištěno, že nástřik pomocí studené kinetizace nezměnil složení původního Ti prášku, kdežto u vrstev deponovaných plazmovým nanášením byla pozorována kompletní transformace na nitridy a oxidy. Vzhledem k rozdílným principům vzniku vrstev a jejich odlišné porozitě byly dále zjištěny zásadní rozdíly v jejich elastických modulech (7.2 GPa u plazmově a 36.7 GPa u kineticky nanesených vrstev). bylo prokázáno, že místa iniciací únavových trhlin a směry jejich šíření v plazmově a kineticky nanesených vrstvách se výrazně odlišují. Na základě získaných poznatků byly v textu navrženy dvě výklady výsledků únavového zatěžování.

This paper presents a summary of the research on the influence of plasma and cold spray deposition of bio-grade Ti powder on the high-cycle fatigue properties of Ti6Al4V substrates. Four sets of flat specimens (as-received, grit-blasted, plasma and cold sprayed) were prepared and subjected to cantilever–beam cyclic bend loading with a constant deflection of the free end. It was found that the grit-blasting procedure significantly increased the fatigue lives of the specimens compared to the as-received set (1.81x increase). The deposition of the coatings onto grit-blasted specimens led to deterioration of fatigue properties. The average fatigue lives of the plasma sprayed and cold sprayed samples reached 1.16x and 0.91x of the as-received specimens, respectively. In order to understand the positive effect of the grit-blasting procedure and the adverse effect of the coatings deposition on fatigue lives, chemical analyses, fractographic analysis, microstructural investigations as well as layers elastic moduli estimation were carried out. It was found that the cold spray deposition retained the composition of the powder feedstock while a complete transformation of Ti into nitrides and oxides was detected in the plasma deposited layers. Owing to the different coating build-up principles and their respective different porosity levels, the moduli of the coatings were found to vary (7.2 GPa for plasma sprayed and 36.7 GPa for cold sprayed layers). The fatigue crack initiation sites and propagation directions in the plasma and cold sprayed specimens were found to differ substantially. Based on the obtained results, two explanations of the fatigue loading results are suggested in the paper., Tento článek představuje shrnutí výsledků výzkumu vlivu plazmového a kinetického nanášení biologických vrstev Ti na únavové vlastnosti substrátů Ti6Al4V. Čtyři vyrobené série vzorků (původní, otryskané, s plazmově nanesenou vrstvou, s vrstvou nanesenou studenou kinetizací) byly vystaveny cyklickému ohybu s krakorcovým upnutím a konstantní výchylkou volného konce. Bylo zjištěno, že procedura tryskání významně prodlužuje únavové životy vzorků ve srovnání s původními tělesy (nárůst až 1.81x). Depozice vrstev na tyto tryskané povrchy vedla ke zhoršení únavových charakteristik. Průměrný únavový život vzorků s plazmově nanesenými vrstvami dosáhl 1.16x a vzorků s vrstvami nanesenými studenou kinetizací 0.91x hodnot původních netryskaných vzorků. Pro pochopení kladného efektu technologie tryskání a negativního efektu depozice nástřiků na únavové životy byla uskutečněna řada analýz (chemické, fraktografické, mikrostrukturální) a byly kalkulovány elastické moduly vrstev. Bylo zjištěno, že nástřik pomocí studené kinetizace nezměnil složení původního Ti prášku, kdežto u vrstev deponovaných plazmovým nanášením byla pozorována kompletní transformace na nitridy a oxidy. Vzhledem k rozdílným principům vzniku vrstev a jejich odlišné porozitě byly dále zjištěny zásadní rozdíly v jejich elastických modulech (7.2 GPa u plazmově a 36.7 GPa u kineticky nanesených vrstev). bylo prokázáno, že místa iniciací únavových trhlin a směry jejich šíření v plazmově a kineticky nanesených vrstvách se výrazně odlišují. Na základě získaných poznatků byly v textu navrženy dvě výklady výsledků únavového zatěžování.

This paper presents a summary of the research on the influence of plasma and cold spray deposition of bio-grade Ti powder on the high-cycle fatigue properties of Ti6Al4V substrates. Four sets of flat specimens (as-received, grit-blasted, plasma and cold sprayed) were prepared and subjected to cantilever–beam cyclic bend loading with a constant deflection of the free end. It was found that the grit-blasting procedure significantly increased the fatigue lives of the specimens compared to the as-received set (1.81x increase). The deposition of the coatings onto grit-blasted specimens led to deterioration of fatigue properties. The average fatigue lives of the plasma sprayed and cold sprayed samples reached 1.16x and 0.91x of the as-received specimens, respectively. In order to understand the positive effect of the grit-blasting procedure and the adverse effect of the coatings deposition on fatigue lives, chemical analyses, fractographic analysis, microstructural investigations as well as layers elastic moduli estimation were carried out. It was found that the cold spray deposition retained the composition of the powder feedstock while a complete transformation of Ti into nitrides and oxides was detected in the plasma deposited layers. Owing to the different coating build-up principles and their respective different porosity levels, the moduli of the coatings were found to vary (7.2 GPa for plasma sprayed and 36.7 GPa for cold sprayed layers). The fatigue crack initiation sites and propagation directions in the plasma and cold sprayed specimens were found to differ substantially. Based on the obtained results, two explanations of the fatigue loading results are suggested in the paper., Tento článek představuje shrnutí výsledků výzkumu vlivu plazmového a kinetického nanášení biologických vrstev Ti na únavové vlastnosti substrátů Ti6Al4V. Čtyři vyrobené série vzorků (původní, otryskané, s plazmově nanesenou vrstvou, s vrstvou nanesenou studenou kinetizací) byly vystaveny cyklickému ohybu s krakorcovým upnutím a konstantní výchylkou volného konce. Bylo zjištěno, že procedura tryskání významně prodlužuje únavové životy vzorků ve srovnání s původními tělesy (nárůst až 1.81x). Depozice vrstev na tyto tryskané povrchy vedla ke zhoršení únavových charakteristik. Průměrný únavový život vzorků s plazmově nanesenými vrstvami dosáhl 1.16x a vzorků s vrstvami nanesenými studenou kinetizací 0.91x hodnot původních netryskaných vzorků. Pro pochopení kladného efektu technologie tryskání a negativního efektu depozice nástřiků na únavové životy byla uskutečněna řada analýz (chemické, fraktografické, mikrostrukturální) a byly kalkulovány elastické moduly vrstev. Bylo zjištěno, že nástřik pomocí studené kinetizace nezměnil složení původního Ti prášku, kdežto u vrstev deponovaných plazmovým nanášením byla pozorována kompletní transformace na nitridy a oxidy. Vzhledem k rozdílným principům vzniku vrstev a jejich odlišné porozitě byly dále zjištěny zásadní rozdíly v jejich elastických modulech (7.2 GPa u plazmově a 36.7 GPa u kineticky nanesených vrstev). bylo prokázáno, že místa iniciací únavových trhlin a směry jejich šíření v plazmově a kineticky nanesených vrstvách se výrazně odlišují. Na základě získaných poznatků byly v textu navrženy dvě výklady výsledků únavového zatěžování.

This paper presents a summary of the research on the influence of plasma and cold spray deposition of bio-grade Ti powder on the high-cycle fatigue properties of Ti6Al4V substrates. Four sets of flat specimens (as-received, grit-blasted, plasma and cold sprayed) were prepared and subjected to cantilever–beam cyclic bend loading with a constant deflection of the free end. It was found that the grit-blasting procedure significantly increased the fatigue lives of the specimens compared to the as-received set (1.81x increase). The deposition of the coatings onto grit-blasted specimens led to deterioration of fatigue properties. The average fatigue lives of the plasma sprayed and cold sprayed samples reached 1.16x and 0.91x of the as-received specimens, respectively. In order to understand the positive effect of the grit-blasting procedure and the adverse effect of the coatings deposition on fatigue lives, chemical analyses, fractographic analysis, microstructural investigations as well as layers elastic moduli estimation were carried out. It was found that the cold spray deposition retained the composition of the powder feedstock while a complete transformation of Ti into nitrides and oxides was detected in the plasma deposited layers. Owing to the different coating build-up principles and their respective different porosity levels, the moduli of the coatings were found to vary (7.2 GPa for plasma sprayed and 36.7 GPa for cold sprayed layers). The fatigue crack initiation sites and propagation directions in the plasma and cold sprayed specimens were found to differ substantially. Based on the obtained results, two explanations of the fatigue loading results are suggested in the paper., Tento článek představuje shrnutí výsledků výzkumu vlivu plazmového a kinetického nanášení biologických vrstev Ti na únavové vlastnosti substrátů Ti6Al4V. Čtyři vyrobené série vzorků (původní, otryskané, s plazmově nanesenou vrstvou, s vrstvou nanesenou studenou kinetizací) byly vystaveny cyklickému ohybu s krakorcovým upnutím a konstantní výchylkou volného konce. Bylo zjištěno, že procedura tryskání významně prodlužuje únavové životy vzorků ve srovnání s původními tělesy (nárůst až 1.81x). Depozice vrstev na tyto tryskané povrchy vedla ke zhoršení únavových charakteristik. Průměrný únavový život vzorků s plazmově nanesenými vrstvami dosáhl 1.16x a vzorků s vrstvami nanesenými studenou kinetizací 0.91x hodnot původních netryskaných vzorků. Pro pochopení kladného efektu technologie tryskání a negativního efektu depozice nástřiků na únavové životy byla uskutečněna řada analýz (chemické, fraktografické, mikrostrukturální) a byly kalkulovány elastické moduly vrstev. Bylo zjištěno, že nástřik pomocí studené kinetizace nezměnil složení původního Ti prášku, kdežto u vrstev deponovaných plazmovým nanášením byla pozorována kompletní transformace na nitridy a oxidy. Vzhledem k rozdílným principům vzniku vrstev a jejich odlišné porozitě byly dále zjištěny zásadní rozdíly v jejich elastických modulech (7.2 GPa u plazmově a 36.7 GPa u kineticky nanesených vrstev). bylo prokázáno, že místa iniciací únavových trhlin a směry jejich šíření v plazmově a kineticky nanesených vrstvách se výrazně odlišují. Na základě získaných poznatků byly v textu navrženy dvě výklady výsledků únavového zatěžování.

This paper presents a summary of the research on the influence of plasma and cold spray deposition of bio-grade Ti powder on the high-cycle fatigue properties of Ti6Al4V substrates. Four sets of flat specimens (as-received, grit-blasted, plasma and cold sprayed) were prepared and subjected to cantilever–beam cyclic bend loading with a constant deflection of the free end. It was found that the grit-blasting procedure significantly increased the fatigue lives of the specimens compared to the as-received set (1.81x increase). The deposition of the coatings onto grit-blasted specimens led to deterioration of fatigue properties. The average fatigue lives of the plasma sprayed and cold sprayed samples reached 1.16x and 0.91x of the as-received specimens, respectively. In order to understand the positive effect of the grit-blasting procedure and the adverse effect of the coatings deposition on fatigue lives, chemical analyses, fractographic analysis, microstructural investigations as well as layers elastic moduli estimation were carried out. It was found that the cold spray deposition retained the composition of the powder feedstock while a complete transformation of Ti into nitrides and oxides was detected in the plasma deposited layers. Owing to the different coating build-up principles and their respective different porosity levels, the moduli of the coatings were found to vary (7.2 GPa for plasma sprayed and 36.7 GPa for cold sprayed layers). The fatigue crack initiation sites and propagation directions in the plasma and cold sprayed specimens were found to differ substantially. Based on the obtained results, two explanations of the fatigue loading results are suggested in the paper., Tento článek představuje shrnutí výsledků výzkumu vlivu plazmového a kinetického nanášení biologických vrstev Ti na únavové vlastnosti substrátů Ti6Al4V. Čtyři vyrobené série vzorků (původní, otryskané, s plazmově nanesenou vrstvou, s vrstvou nanesenou studenou kinetizací) byly vystaveny cyklickému ohybu s krakorcovým upnutím a konstantní výchylkou volného konce. Bylo zjištěno, že procedura tryskání významně prodlužuje únavové životy vzorků ve srovnání s původními tělesy (nárůst až 1.81x). Depozice vrstev na tyto tryskané povrchy vedla ke zhoršení únavových charakteristik. Průměrný únavový život vzorků s plazmově nanesenými vrstvami dosáhl 1.16x a vzorků s vrstvami nanesenými studenou kinetizací 0.91x hodnot původních netryskaných vzorků. Pro pochopení kladného efektu technologie tryskání a negativního efektu depozice nástřiků na únavové životy byla uskutečněna řada analýz (chemické, fraktografické, mikrostrukturální) a byly kalkulovány elastické moduly vrstev. Bylo zjištěno, že nástřik pomocí studené kinetizace nezměnil složení původního Ti prášku, kdežto u vrstev deponovaných plazmovým nanášením byla pozorována kompletní transformace na nitridy a oxidy. Vzhledem k rozdílným principům vzniku vrstev a jejich odlišné porozitě byly dále zjištěny zásadní rozdíly v jejich elastických modulech (7.2 GPa u plazmově a 36.7 GPa u kineticky nanesených vrstev). bylo prokázáno, že místa iniciací únavových trhlin a směry jejich šíření v plazmově a kineticky nanesených vrstvách se výrazně odlišují. Na základě získaných poznatků byly v textu navrženy dvě výklady výsledků únavového zatěžování.

The U.S. Army has experienced significant corrosion problems with magnesium (Mg) alloys that are used to fabricate aircraft components. The most severe of these are associated with large and expensive transmission and gearbox housings for rotorcraft, which have to be removed prematurely because of corrosion. Many of the parts cannot be reclaimed because there is not technology that can restore them adequately for service. The U.S. Army Research Laboratory (ARL) has developed a Cold Spray process to reclaim Mg components that shows significant improvement over existing methods. Part of this program has demonstrated and validated a Cold Spray (supersonic particle deposition) process using aluminum (Al) and/or alloys as a cost-effective, environmentally acceptable technology to provide surface protection and a repair/rebuild methodology to a variety of Mg alloy components for use on Army and Navy helicopters and advanced fixed-wing aircraft., The original document contains color images.

The U.S. Army Research Laboratory at Aberdeen Proving Ground, MD, has developed a novel process for repairing and rebuilding damaged aluminum components using Supersonic Particle Deposition, commonly referred to as cold spray. A Centerline Model No. SSM-P3300 Portable Cold Spray Deposition System was used to deposit a highly adherent, dense aluminum composite material to repair corrosion damage pits and rebuild the snap ring groove and gear teeth on the mast support on an Army helicopter. ARL performed microstructural analysis as well as adhesion, fatigue, and corrosion tests to evaluate the characteristics of the cold spray aluminum composite coatings. The cold spray deposited material was subsequently machined using conventional machining tools to dimensionally restore the component to its original condition. Final testing and approval for implementation of this repair procedure is in progress., Prepared in collaboration with Data Matrix Solutions, Inc. The original document contains color images.

The U.S. Army has experienced significant corrosion problems with magnesium alloys that are used to fabricate aircraft components. The most severe of these are associated with large and expensive transmission and gearbox housings for rotorcraft, which have to be removed prematurely because of corrosion. Many of the parts cannot be reclaimed because there is not an existing technology that can restore them adequately for service. The U.S. Army Research Laboratory has developed a cold spray process to reclaim magnesium components that shows significant improvement over existing methods and is in the process of qualification for use on rotorcraft. The cold spray repair has been shown to have superior performance in the tests conducted to date, is inexpensive, can be incorporated into production, and has been modified for field repair, making it a feasible alternative over competing technologies. Cold spray trials were performed using aluminum powders at different deposition conditions with both helium and nitrogen carrier gas. Evaluations of the resultant cold spray aluminum coatings deposited on ZE-41A magnesium alloy substrates were conducted using microstructural analysis, hardness, bond strength, and corrosion testing., The original document contains color images.

Cold gas dynamic spraying (CGDS), a relatively new thermal spraying technique has drawn a lot of attention due to its inherent capability to deposit a wide range of materials at relatively low-operating temperatures. A De Laval nozzle, used to accelerate the powder particles, is the key component of the coating equipment. Knowledge concerning the nozzle design and effect of process parameters is essential to understand the coating process and to enable selection of appropriate parameters for enhanced coating properties. The present work employs a one-dimensional isentropic gas flow model in conjunction with a particle acceleration model to calculate particle velocities. A laser illumination-based optical diagnostic system is used for validation studies to determine the particle velocity at the nozzle exit for a wide range of process and feedstock parameters such as stagnation temperature, stagnation pressure, powder feed rate, particle size and density. The relative influence of process and feedstock parameters on particle velocity is presented in this work. © ASM International 2008.