Search

In the present work, Fe66Cr10Nb5B19 metallic glass coatings deposited by detonation spraying (DS) on carbon steel substrates were structurally characterized and tested in 3.5 wt.% NaCl solutions with pH values of 3.0, 5.5, and 10.0 under potentiodynamic polarization conditions. The coatings had low porosity (2.9-4.5%) and showed a predominantly amorphous structure. The concentration of an amorphous phase in the detonation coatings was 97.5-99.5 wt.%. Such high concentrations were not observed in thermally sprayed Fe-Cr-Nb-B coatings obtained by other research groups. Under the test conditions, the coatings exhibited low corrosion current densities (of the order of 10-6 A cm-2) and low passive current densities (below 10-3 A cm-2) while showing extended passive regions (stable within 1.5 V from the corrosion potential). The Fe66Cr10Nb5B19 coatings produced by DS showed a much better corrosion resistance than the carbon steel substrate. Furthermore, the corrosion resistance of the Fe66Cr10Nb5B19 DS coatings was superior to that of flame-sprayed or high-velocity oxygen fuel-sprayed Fe-Cr-Nb-B coatings reported to date. These results open new prospects for the use of affordable and Cr-lean Fe-Cr-Nb-B glassy coatings for carbon steel protection, where chloride-induced corrosion is the major degradation risk, such as metallic components for marine applications.

This work deals with iron-based amorphous alloys in the form of coatings and sintered materials. It compares the structure and properties of Fe-Cr-Nb-B alloys (Fe66Cr10Nb5B19 and Fe62Cr10Nb12B16) produced by detonation spraying and spark plasma sintering. The Fe66Cr10Nb5B19 alloy has a higher glass-forming ability than Fe62Cr10Nb12B16 and the gas-atomized Fe66Cr10Nb5B19 feedstock powder was mainly amorphous, while the Fe62Cr10Nb12B16 powder with the same particle size range was fully crystalline. Detonation spraying made it possible to produce coatings with an amorphous phase as the main phase with both powders. The microhardness of the Fe66Cr10Nb5B19 coatings was lower than that of the Fe66Cr10Nb5B19 sintered alloy, at the same level of porosity (< 1%). The wear resistance of the Fe66Cr10Nb5B19 coatings was higher than that of the sintered Fe66Cr10Nb5B19 alloy. Fe66Cr10Nb5B19 and Fe62Cr10Nb12B16 coatings showed close values of microhardness and wear resistance under dry linearly reciprocating conditions. Notably, the wear resistance of the coatings was higher than that of stainless steel. This work demonstrated that detonation spraying is suitable for manufacturing amorphous phase-based alloy coatings, even for compositions with moderate glass-forming ability.

In this work, we traced structural transformations of an Al62.5Cu25Fe12.5 alloy, in which a quasicrystalline icosahedral phase (i-phase) can be formed, upon spraying onto a substrate and consolidation from the powder into the bulk state. The Al62.5Cu25Fe12.5 powder was obtained by gas atomization and consisted of i-phase and ?-phase AlCu(Fe). The powder was detonation sprayed (DS) and consolidated by spark plasma sintering (SPS)/hot pressing (HP). During DS, the particles experienced partial or complete melting and rapid solidification, which resulted in the formation of coatings of a complex structure. The composite regions containing i-phase were inherited from the powder alloy. The fraction of the material that experienced melting solidified as ?-phase AlFe(Cu) in the coating. It was suggested that the difficulty of obtaining i-phase upon post-spray annealing is related to aluminum depletion of the alloy during DS. During SPS and HP, the elemental composition of the alloy was preserved, while the exposure to an elevated temperature led to phase homogenization. SPS and HP conducted at 700?C resulted in full densification and the formation of a single-phase quasicrystalline alloy. The sintered single-phase alloy showed a higher microhardness in comparison with the DS coatings.

Cast Al(5.5 to 6.3 wt pct)Si-(3.1 to 3.7 wt pct)Cu alloys containing 0.6 and 1.2 wt pct Fe were processed by spray forming, rotary swaging, and homogenization/solution heat treatment, which led to a tensile ductility of 16 pct. Such outstanding ductility is ascribed to the microstructure formed: globular silicon particles, refined iron-rich intermetallics, and a supersaturated solid solution of Cu in the α-Al matrix that promoted dynamic strain aging and homogenization of the deformation process.

A metastable beta TMZF alloy was tested by isothermal compression under different conditions of deformation temperature (923 to 1173 K), strain rate (0.172, 1.72, and 17.2 s−1), and a constant strain of 0.8. Stress–strain curves, constitutive constants calculations, and microstructural analysis were performed to understand the alloy’s hot working behavior in regards to the softening and hardening mechanisms operating during deformation. The primary softening mechanism was dynamic recovery, promoting dynamic recrystallization delay during deformation at higher temperatures and low strain rates. Mechanical twinning was an essential deformation mechanism of this alloy, being observed on a nanometric scale. Spinodal decomposition evidence was found to occur during hot deformation. Different models of phenomenological constitutive equations were tested to verify the effectiveness of flow stress prediction. The stress exponent n, derived from the strain-compensated Arrhenius-type constitutive model, presented values that point to the occurrence of internal stress at the beginning of the deformation, related to complex interactions of dislocations and dispersed phases.

At present, metallic glasses are evaluated as alternative reinforcements for aluminum matrix composites. These composites are produced by powder metallurgy via consolidation of metallic glass-aluminum powder mixtures. In most studies, the goal has been to preserve the glassy state of the reinforcement during consolidation. However, it is also of interest to track the structure evolution of these composites when partial interaction between the matrix and the metallic glass is allowed during sintering of the mixtures. The present work was aimed to study the microstructure and mechanical properties of composites obtained by spark plasma sintering (SPS) of Al-20 vol.% Fe66Cr10Nb5B19 metallic glass mixtures and compare the materials, in which no significant interaction between the matrix and the Fe-based alloy occurred, with those featuring reaction product layers of different thicknesses. Composite materials were consolidated by SPS at 540 and 570 °C. The microstructure and mechanical properties of composites obtained by SPS and SPS followed by forging, composites with layers of interfacial reaction products of different thicknesses, and metallic glass-free sintered aluminum were comparatively analyzed to conclude on the influence of the microstructural features of the composites on their strength.

This work studied the corrosion behaviour of Ti-12Mo-6Zr-2Fe alloy with different surface conditions: untreated and chemically treated (CST), anodised nanotubes (Nt) and nanopores (NP). These samples were immersed in simulated body fluid (SBF) for 1, 7, and 14 days. Samples with Nt and NP displayed higher corrosion resistance and lower passivation current (ipass) than untreated and CST samples after 14 days resting in SBF. Furthermore, traditional equivalent circuits and a new two-channel transmission line model were employed to efficiently simulate the electrochemical impedance spectroscopy (EIS) data of the different surface conditions.

The temperature and dynamic pressure of the detonation products are parameters that determine the heating and acceleration of particles during the detonation spraying. These parameters depend on the composition of the explosive mixture. The present article reports the influence of the composition of the acetylene–oxygen explosive mixture on the structure and properties of detonation coatings obtained from a multi-component Fe-based alloy. A gas-atomized powder with a nominal composition of Fe66Cr10Nb5B19 was used for depositing the coatings. The O2/C2H2 molar ratio was 1.1; 1.5 or 2.0; the volume of the explosive mixture was constant. At an O2/C2H2 ratio of 1.1, the coating was 99% amorphous. As the O2/C2H2 ratio was increased, the content of the crystalline phase in the coatings increased. At higher oxygen contents, oxidation of the particle surfaces during spraying is more likely. Possibly, oxide films formed in-situ may act as heterogeneous nucleation sites for crystallization, which leads to a decrease in the content of the amorphous phase in the coatings. The increase in the O2/C2H2 ratio from 1.1 to 2.0 also leads to increased porosity and decreased coating microhardness.

Here we report for the first time that the anodization of the biphasic (α'+β) Ti13Nb13Zr alloy form arrays of TiO2 nanotubes with well-defined circular geometry in the α′ phase, while nanopores of TiO2 are formed in the β phase. Samples of the Ti13Nb13Zr alloy were severely plastic deformed using High-Pressure Torsion (HPT) to refine the microstructure and to redistribute α′ and β phases. The anodization was performed using an organic electrolyte (glycerol) containing fluoride ions and a few percentages of water. All the specimens coated with nanotubes were annealed at 550 °C to crystallize the modified surface of the as-anodized samples. XRD analyses confirmed that the as-anodized amorphous nanostructures crystallize in a mixture of anatase and rutile after heat treatment, and SEM observations showed no significant morphological changes in the surface phases. The evaluation of corrosion resistance showed that anodized samples have much better corrosion properties than polished ones without any evidence of pitting corrosion. Quantitative comparison between anodized coarse-grained (α'+β)-Ti alloy and ultra-fine grained (α'+β)-Ti one showed that the nanostructuring of the (α'+β)-Ti alloy by HPT helped to improve the bioactivity when compared with the coarse-grained sample.

Ti alloys have been intensely used for human implants due to its excellent characteristics, like bio-inertness, low density, and corrosion resistance. However, some alloying elements were found to be toxic for the human body, which restricts the use of some alloys. Furthermore, there are two additional and essential aspects to be considered. The first relates to the young modulus that, despite being lower than other alloys commonly used for this purpose, it is still far over from the human bone modulus. Such high modulus can result in the stress shield phenomena and the consequent implant losing. The second aspect relates to the fact that bio-inertness does not guarantee a complete tissue integration to the implant and, consequently, the expected implant performance. In this context, new low modulus b-Ti alloys containing nontoxic elements have been developed in recent years, and several surface modification processes have been proposed to promote better implant/tissue integration.In the present work, the new b-type Ti-Mo-Zr-Fe alloy has been submitted to a plasma enhanced chemical vapor deposition (PECVD) process in order to form a superficial titanium nitride layer, aiming to produce a satisfactory substrate for the tissue cells growing. In a first step, microstructural characterization and corrosion performance of the modified alloy surface has been evaluated by Electrochemical Impedance Spectrometry and Potentiodynamic testing, and the results compared to the unmodified alloy. It was found that during the plasma nitriding process, that runs at 550°C for 1h, the metastable b microstructure is partially converted into a’ and possibly a” phases, which can impact the young modulus. The 500nm thick TiN layer formed over the alloy surface improved the corrosion behavior of the alloy. These results encourage the continuity of the research, with the future in vitro bio-activity testing of the nitrided surface.

Background Nanophase surface properties of titanium alloys must be obtained for a suitable biological performance, particularly to facilitate cell adhesion and bone tissue formation. Obtaining a bulk nanostructured material using severe plastic deformation is an ideal processing route to improve the mechanical performance of titanium alloys. By decreasing the grain size of a metallic material, a superior strength improvement can be obtained, while surface modification of a nanostructured surface can produce an attractive topography able to induce biological responses in osteoblastic cells. Methods Aiming to achieve such an excellent synergetic performance, a processing route, which included equal channel angular pressing (ECAP), hot and cold extrusion, and heat treatments, was used to produce a nanometric and ultrafine-grained (UFG) microstructure in the Ti-6Al-7Nb alloy (around of 200 nm). Additionally, UFG samples were surface-modified with acid etching (UFG-A) to produce a uniform micron and submicron porosity on the surface. Subsequently, alkaline treatment (UFG-AA) produced a sponge-like nanotopographic substrate able to modulate cellular interactions. Results After several kinds of biological tests for both treatment conditions (UFG-A and UFG-AA), the main results have shown that there was no cytotoxicity, expressed alkaline phosphatase activity and total protein amounts without statistical differences compared to control. However, the UFG-AA samples presented an attractive effect on the cell membranes, and cell adhesions were preferentially induced as compared with UFG-A. Both conditions demonstrated cell projections, but for UFG-AA, cells were more widely dispersed, and more quantities of filopodia formation could be observed. Conclusion Herein, the reasons for such behaviors are discussed, and further results are presented in addition to those mentioned above.

The TiNbZrHfTa high entropy alloy was studied for its use as a base material for orthopedic implants. The alloy produced by arc melting contains only biocompatible elements and has an attractive combination of mechanical properties with a tensile strength of 1050 MPa and Young's modulus of 66 GPa. Surface modification techniques were carried out to bioactivate the alloy surface, ensuring better interaction between the implanted material and the human body. The first technique was the anodization in an organic electrolyte, containing F- ions in different potentials and time, obtaining the best condition at 10 V potential for 2 h at 20 °C, producing an ordered and adherent nanotubular morphology to the substrate. The second technique was precalcification. Using the alternation immersion method (AIM), the saturation and nucleation of Ca-P deposits were guaranteed, providing high deposition rates of hydroxyapatite (HAP) when immersed in simulated body fluid (SBF) solution. Structural characterizations were performed by XRD and XPS. Morphological analyses were performed by SEM and chemical semi-quantitative analyses by EDX. Corrosion resistance properties were performed through polarization and impedance curves. The TiNbZrHfTa high entropy alloy proved to be a competitive and attractive candidate in the research for new compositions to replace conventional alloys, having biocompatibility, high strength, and low Young's modulus, reducing stress shielding effects and showing good bioactivity characteristics through the surface modification techniques presented here.

Ricardo Pereira Nogueira,1,2 Jose Deuzimar Uchoa,3,4 Fanny Hilario,2 Gabriela de Fátima Santana-Melo,5 Luana Marotta Reis de Vasconcellos,5 Fernanda Roberta Marciano,6 Virginie Roche,2 Alberto Moreira Jorge Junior,2,7 Anderson Oliveira Lobo4 1Chemical Engineering Department, Khalifa University of Science and Technology, Abu Dhabi 127788, United Arab Emirates; 2Université Grenoble Alpes, Université Savoie Mont Blanc, CNRS, GrenobleINP*LEPMI, Grenoble 38000, France; 3Federal Institute of Education, Science and Technology of Piauí, Teresina 64053-390, Brazil; 4Interdisciplinary Laboratory for Advanced Materials, BioMatLab Group, Materials Science and Engineering Graduate Program, UFPI – Federal University of Piaui, Teresina 64049-550 Brazil; 5Department of Bioscience and Oral Diagnosis, Institute of Science and Technology, Sao Paulo State University, Sao José dos Campos 12245-000, Brazil; 6Department of Physics, Federal University of Piaui, Teresina PI 64049-550 Brazil; 7Department of Materials Engineering, Federal University of São Carlos, São Carlos 13565-905, BrazilCorrespondence: Anderson Oliveira LoboCampus Universitário Ministro Petrônio Portella, Av. Universitária, s/n, Centro de Tecnologia, Laboratório Interdisciplinar de Materiais Avançados, Ininga, Teresina, PI 64049-550, BrazilTel +55 86 32371057Email lobo@ufpi.edu.brBackground: Nanostructured surface modifications of Ti-based biomaterials are moving up from a highly-promising to a successfully-implemented approach to developing safe and reliable implants.Methods: The study’s main objective is to help consolidate the knowledge and identify the more suitable experimental strategies related to TiO2 nanotubes-modified surfaces. In this sense, it proposes the thorough investigation of two optimized nanotubes morphologies in terms of their biological activity (cell cytotoxicity, alkaline phosphatase activity, alizarin red mineralization test, and cellular adhesion) and their electrochemical behavior in simulated body fluid (SBF) electrolyte. Layers of small-short and large-long nanotubes were prepared and investigated in their amorphous and crystallized states and compared to non-anodized samples.Results: Results show that much more than the surface area development associated with the nanotubes’ growth; it is the heat treatment-induced change from amorphous to crystalline anatase-rutile structures that ensure enhanced biological activity coupled to high corrosion resistance.Conclusion: Compared to both non-anodized and amorphous nanotubes layers, the crystallized nano-structures’ outstanding bioactivity was related to the remarkable increase in their hydrophilic behavior, while the enhanced electrochemical stability was ascribed to the thickening of the dense rutile barrier layer at the Ti surface beneath the nanotubes.Keywords: surface modification, TiO2 nanotubes, commercially pure titanium, bioactivity

The metastable β-type Ti-12Mo-6Zr-2Fe alloy was subjected to an assessment of its fatigue mechanical behavior. Promising tensile and fatigue properties were obtained when the alloy was solution treated and quenched, because nanocrystalline particles of ω phase were formed throughout the β matrix. When the material was subjected to a protocol of chemical etching and a subsequent surface polishing, the fatigue limit decreased significantly as a result of H pick-up, although the tensile properties were not changed. The increase of the local H concentration caused the precipitation of fine hydrides at high-energy grain boundaries. Fatigue crack initiation changed to a subsurface mode induced by the cleavage of hydride precipitates.

Hot torsion tests were carried out to simulate the industrial thermomechanical processing of two austenitic steels for bioimplant applications, namely ISO 5832-9 and ASTM F138. The former has Ti, Nb, and V in the composition, being N-rich. However, the latter is Ni-richer and without extra alloying element additions. Special attention was paid to the effect of interpass times, particularly to the soaking temperature, which was reduced to decrease processing times and costs. Optical and electron microscopy, corrosion tests, and hardness measurements were used to characterize the effect of the above processing parameters on both alloys. No significant increase in processing loads was noticed after the reduction of the reheating temperature. This was explained in terms of the balance between partial particles dissolution and the increment in the solute drag effect provided by the elements put into solution. Such an increment in solid solution favored the dynamic recovery process, delaying the dynamic recrystallization one. However, strain-induced precipitation took place at lower temperatures, by using the extra N and Cr delivered to the matrix, and limiting the recrystallization softening. The rolling schedule promoted abundant grain refinement. The final grain size ranged from 2.5 to 11 &micro, m, depending on reheating temperature, interpass time, presence of alloying elements, and N. In general terms, the corrosion resistance of the ISO steel soaked at the lowest temperature (1200 &deg, C) was better than when reheated to the highest one (1250 &deg, C). On the contrary, the F138 steel had worse corrosion behavior.

We show that, using thermo -elastic processing, metallic -glass foils can be shaped, without being embrittled, into linear and annular wave springs. These springs exhibit an undulatory behaviour, unique to metallic -glass foils, in which under compression the number of arcs in the spring increases, increasing the load -bearing capacity and the spring constant. We evaluate the performance limits of the metallic -glass wave springs, and consider how the undulatory behaviour can be exploited. The metallic -glass springs can operate over the same load -ranges as commercially available crystalline wave springs, but have material volumes (and therefore weights) that are one to two orders of magnitude less. Their energy storage per unit material volume is as high as 2600 kJ m – 3 . We suggest that the undulatory behaviour is important in rendering the springs fail -safe in case of overload. We discuss the range of applicability of thermo -elastic processing, the likely working limit of metallic -glass wave springs, and the potential for application of metallic -glass springs in MEMS devices.

International audience; In this study, we describe an experimental setup and a new approach for operando investigation of structural evolution of materials during wear and friction. The setup is particularly suited for testing various friction pairs, including those in which both rubbing bodies are made of metals. The developed device allows circumventing the problems related to significant scattering of X-rays produced by metals and makes it possible using “real samples” in synchrotron beamlines operating in reflection mode. To demonstrate the capabilities of the device and the proposed new approach, an iron-based massive sample was subjected to thousands of friction cycles using a cemented carbide pin. The material was probed with synchrotron X-ray radiation within a few milliseconds after leaving the friction zone. The results of the microstructural and structural analysis, as well as results obtained from diverse mathematical models, allowed us to evaluate several features, including gradual accumulation of defects, microstructural refinement, dislocation density changes, surface layer oxidation, as well as several other phenomena caused by the dry sliding friction process. Mainly, it was possible to conclude that the process of wear occurred due to the cooperative action of oxidation and plastic deformation, which began during the first cycle of frictional interaction and was manifested in increasing the dislocation density, whose type was changed gradually during testing. The number of defects quickly reached a threshold value and subsequently fluctuated around it due to periodically repeated processes of defect accumulation and stress relaxation resulting from material wear. It was also observed that friction led to the quick formation of a mechanically mixed layer, consisting of the sample material and a mixture of two types of iron oxide – hematite and magnetite. The delamination of this layer was probably the primary wear mechanism.

It is well known that a balance between the generation of low-angle and high-angle grain boundaries (LABG and HAGB) is achieved in materials undergoing a severe plastic deformation (SPD) process. It is also observed that most annealed materials evolve from a substantial fraction of LAGB at the early deformation steps towards a steady state in which an equilibrium between LAGB and HAGB fractions is attained. In the present work, such a balance is analyzed for different alloys, i.e., Cu, Al, and Fe based. A mathematical expression is proposed for the amount of LAGB and HAGB as a function of the strain impaired which in turn can be used to predict the number of passes (especially for ECAP) or the amount of total deformation for any SPD process necessary to attain a steady microstructure. The model seeks to serve as a first approximation of the mechanical and microstructural properties of ultrafine grain metal materials.

Al3Ti-based alloys attract exceptional attention due to their high specific mechanical properties. However, their application is still insufficient due to their low ductility and fracture toughness. Several approaches were previously proposed to address these problems. The first one is stabilization of the cubic modification of titanium trialuminide by alloying. Another approach consists in fabricating metal-intermetallic laminated composites (MIL). In this study, we combined both methods to synthesize the first MIL composite with cubic Al3Ti interlayers. Copper additions were used to stabilize the cubic modification of Al3Ti and produce a novel Ti-Al5CuTi2 MIL composite. First mechanical characterization by indentation tests showed that the binary Al3Ti intermetallic tended to crack at a load of 0.2 kg while the fracture was not observed in the Al5CuTi2 layers at least at a load of 1 kg. These results are an indirect evidence of a higher ductility and fracture toughness of the composite with cubic Al3Ti compared to tetragonal one. The sequence of the phase transformations in the Al-Ti-Cu system was studied using in situ synchrotron X-ray radiation diffraction. The formation of Al5CuTi2 occurred via several intermediate stages including eutectic melting of Al and Cu and the formation of binary AlCu and Al3Ti compounds. Keywords: Sintering, Titanium aluminide, Phase transformation, Synchrotron diffraction, Fracture toughness, Ternary compound

Mechanically milled FeCrNbB feedstock powders from commercial precursors were used to produce amorphous coatings through two different industrial thermal-spraying techniques: high-velocity oxygen fuel (HVOF) and flame spraying. Microstructure, thermal behavior, and hardness of the coatings and their corrosion resistances in acidic and alkaline chloride-rich media were comparatively studied. HVOF process was effective to produce ~ 200-µm-thick highly amorphous coatings with hardness over than 700 HV0.3 and low porosity (~ 5 pct). Flame-sprayed ~ 220-µm-thick coatings were nanocrystalline, composed of α-Fe, Fe2B, FeNbB, and Fe2O3 phases and presented hardness of 564 HV0.3 and ~ 10 pct porosity. Electrochemical measurements indicated that HVOF coatings exhibit higher corrosion resistance than flame-sprayed ones thanks to the higher amorphous content and lower porosity resulting from the former processing route. Electrochemical impedance spectroscopy results demonstrated that amorphous HVOF Fe60Cr8Nb8B24 (at. pct) coatings are interesting to protect mild steels such as the API 5L X80 against corrosion in chloride-rich environments.