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Laser shock peening (LSP) of Al 2 O 3 armour ceramics is reported for the first-time. A 10 J, 8 ns, pulsed Nd:YAG laser with a 532 nm wavelength was employed. The hardness, K Ic , fracture morphology, topography, surface residual stresses and microstructures were investigated. The results showed an increase in the surface hardness by 10% which was confirmed by a reduction in Vickers indentations size by 5%. The respective flaw sizes of the Vickers indentations were also reduced (10.5%) and inherently increased the K Ic (12%). Residual stress state by X-ray diffraction method showed an average stress of − 64 MPa after LSP, whilst the untreated surface stress measured + 219 MPa. Further verification with the fluorescence method revealed surface relaxation with a maximum compressive stress of − 172 MPa induced after LSP within the Al 2 O 3 armour ceramic. These findings are attributed to a microstructural refinement, grain size reduction and an induction of compressive stress that was relaxing the top/near surface layer (post LSP) from the pre-existing tensile stresses. Further process refinement/optimization will provide better control of the surface properties and will act as a strengthening technique to improve the performance of armour ceramics to stop bullets for a longer period of time and protect the end-users. [ABSTRACT FROM AUTHOR]

It is challenging to tailor the mechanical properties of in-situ formed β phases in Ti/Zr-based bulk metallic glass composites (β-type BMGCs) without changing the morphologies of the β phases. Recently, BMGCs containing metastable β-Ti/Zr phases (metastable β-type BMGCs) exhibit an exothermic reaction below the glass transition temperature (sub- T g ) of the glassy matrices during heating, however, the corresponding structural origin remains unclear. In this work, the precipitation of ω phase inside β phase was revealed to account for the sub- T g exothermic event of the metastable Ti 45.7 Zr 33 Cu 5.8 Co 3 Be 12.5 BMGC. The sub- T g annealing of metastable β-type BMGCs causes the precipitation of nanometer-sized isothermal ω phase, which leads to a large increase in the modulus and hardness of the crystalline phase. This finding provides a novel route to tailor the modulus and hardness of the crystalline phases in BMGCs without changing their morphologies, including volume fractions, sizes, and distributions. On this basis, the influence of the modulus and hardness of the crystalline phase on mechanical properties of BMGCs was exclusively investigated. Our experimental results together with finite-element simulations proved that lower modulus and hardness of the crystalline phase benefit a larger plasticity of BMGCs. [ABSTRACT FROM AUTHOR]

The hardness, strength, and abrasion resistance of copper for electrical contact materials is poor. Thus, we aligned carbon nanotubes in Cu matrix composites through die-stretching for their excellent mechanical properties and abrasion resistance. The Cu matrix composites with varying CNTs volume fraction from 0 to 10 vol.% were fabricated under protective atmosphere sintering of a mixture of Cu powders and Ni/Cu coated CNTs. This was followed by forging and die-stretching. The CNTs were uniformly dispersed in the dense composites, and the trend of their alignment along the stretching direction was obvious. The composites were anisotropic, and their mechanical properties and abrasion resistance increased obviously with the addition of CNTs. The 5 vol.% CNTs/Cu composite showed the best hardness, tensile strength, and abrasion resistance. The mechanisms underlying the improved mechanical and tribological behavior were evaluated, and this research provides novel ideas and technology for the distribution and directional alignment of CNTs in the matrix. [ABSTRACT FROM AUTHOR]

The present work develops a numerical approach combining thermodynamic and kinetic simulations to investigate the austenitisation process on spheroidised bearing steel. The approach incorporates the dissolution of spheroidised cementite present prior to austenitisation and the influence of austenitisation temperature. It allows predictions including the chemical driving force of austenite formation, the evolution of phase constituents and their chemical compositions during austenitisation, as well as an assessment on the austenite stability upon quenching. The calculated results further allow to predict the hardness of the produced martensitic steels. The model predictions are validated against experimental data in two commercial bearing steels with six austenitisation processes. Good agreement between the experimental results and numerical predictions is obtained on the steel microstructure, austenite stability and material hardness. In addition, comparison of the two steels show that 100Cr6 requires to be austenitised at temperatures 10 °C higher than 100CrMnSi6-4, to achieve the same driving force for austenite formation, and 20 °C higher to achieve identical austenite stability upon quenching. The method can be adopted beyond bearing steels to design austenitisation processing schedules. [ABSTRACT FROM AUTHOR]

Al91Fe4Cr5 quasicrystal (QC) reinforced α-Al matrix composite materials from the mixture of pure aluminum and Al65Cu20Fe10Cr5 QC powders were prepared by Selective Laser Melting (SLM) which can produce parts with sophisticated form and fine microstructure with near-zero material waste. The effects of process parameters (such as laser power and scanning speed) on the microstructure, hardness and wear behavior of SLMed composites were investigated with a special focus on the size and morphology of Al 91 Fe 4 Cr 5 QC reinforcement. After laser melting process, an Al-rich QC phase (Al 91 Fe 4 Cr 5 ) is formed. The grain size increases and its morphology changes from spherical to irregular with increment of laser power. Additionally, the sample obtained at relatively low laser power presents a mixed microstructure (partially melted QC, micro-QC and nano-QC) and high wear resistance. The instrumented indentation tests indicate that the partially melted QC particle present higher hardness than that of the other structure in the composite. Moreover, the wear mechanism changes from oxidation to delamination as the laser power increases. [ABSTRACT FROM AUTHOR]

The microstructural, mechanical and corrosion behavior of the surface of an AA6181-T4 aluminum alloy overlap welded onto Ti-6Al-4V titanium alloy by friction spot welding (FSpW) was analyzed based on optical microscopy (OM), scanning electron microscopy (SEM), microhardness and potentiodynamic polarization techniques. The results indicated that the FSpW process modified the microstructure of the AA6181-T4 aluminum alloy, as indicated mainly by the size, type and quantity of precipitates in various welding regions. The microhardness tests showed similar hardness values in the stir zone (SZ) and base metal (BM), which was ascribed to the breakdown and homogenization of precipitates in the SZ. On the other hand, the heat affected zone (HAZ) showed the lowest hardness, which was attributed to the coalescence of Mg 2 Si precipitates caused by the thermal cycle of the welding process. The potentiodynamic polarization tests indicated that the SZ showed the highest pitting potential due to the refined microstructure in this zone. SEM images recorded after potentiodynamic polarization testing indicated that preferential sites for pitting nucleation were regions adjacent to the Al (Fe, Si, Mn, Mg) precipitates, and the mildest corrosive attack was found in the SZ. [ABSTRACT FROM AUTHOR]

[Display omitted] • Feasibility of short time induction hardening of high strength steels. • Dilatometric prove of sufficiency of short time hardening cycles. • Correlation with state of the art transient tempering modelling. • Transfer of laboratory heat treatmentto industrial induction hardening plant. High-speed steels (HSS) such as AISI M2 are generally used for cutting and forming tools or broaches with the highest demands on load bearability and hot-hardness. The requirements for high-speed steels are, on the one hand, extremely high hardnesses of over 800–900 HV and, on the other hand, the thermal stability of the microstructure up to 500 °C. This combination is achieved by complex precipitation-hardenable iron-based alloys. Common heat treatment practices for high-speed steels use salt baths or vacuum ovens, which are energetically unfavorable and require subsequent cleaning. The study consists of short-time hardening and short-time tempering on a laboratory scale by means of dilatometry and thereupon an implementation in an industrial induction hardening machine. The laboratory scale experiments demonstrate the feasibility of bringing sufficient alloying elements into solution by means of several heat treatment cycles despite short holding times of 1 s and less. Combined tests of short time hardening and tempering show a hardness of up to 850 HV10 that are competitive with the conventional heat treatment route. First attempts to transfer the process to an industrial setup exhibit some peculiarities in the process control, but reveal promising results with a surface hardness of up to 750 HV10. [ABSTRACT FROM AUTHOR]

[Display omitted] • A Residual Convolutional Neural Network (Res-Net) model was employed to predict indentation modulus and hardness of cement paste from BSE images. • A dataset comprising 40,000 nanoindentation results and 40,000 BSE images was built to train the model. • The resulting Res-Net model can precisely predict the elastic modulus and hardness with a R2 of 0.85 and 0.88. • Deconvolution of Res-Net prediction obtains similar invariant statistics as tested by experiments, which gives strong evidence of the applicability of the Res-Net model. This paper employs computer vision techniques to predict the micromechanical properties (i.e. , elastic modulus and hardness) of cement paste based on an input of Backscattered Electron (BSE) images. A dataset comprising 40,000 nanoindentation tests and 40,000 BSE micrographs was built by express nanoindentation test and Scanning Electron Microscopy (SEM). A Residual Convolutional Neural Network (Res-Net) model, which differs from a typical Convolutional Neural Network (CNN) architecture by a shortcut connection, was employed and compared with a simple table model. The models were trained, tuned, and tested over a training, validation and testing set comprising 70%, 15% and 15% of the 40,000 data pairs, respectively. The following conclusions were drawn: 1) Express nanoindentation tests can provide reliable information for cement paste. Deconvolution based on Gaussian Mixture Model (GMM) can obtain almost invariant statistics for each phase; 2) Based on averaged greyscale values of each BSE image, a table model can predict the elastic modulus and hardness with R2 of 0.80 and 0.83, respectively; 3) Based on the intensity of each pixel as well as their patterns in each BSE image, the Res-Net model can predict the elastic modulus and hardness with a R2 of 0.85 and 0.88, respectively. Deconvolution of the Res-Net prediction obtains similar invariant statistics as derived by the nanoindentation tests, which gives strong evidence of the applicability of the Res-Net model. [ABSTRACT FROM AUTHOR]

Plasma transferred arc technique was used for the surface modification of 14.5 wt%-Cr cast iron. The objective of this work was to investigate the microstructural and hardness changes, caused by plasma surface melting and post heat treatment. The processing parameters were: arc current 250 A, voltage 60 V, working gas – argon, scanning speed: 0.25 m/min which ensured the surface temperature about 1500 °C. The study involved optical microscopy, SEM/EDS, XRD, Finite element modeling (FEM), Thermo-Calc calculations and microhardness measurements. A modified melted layer of about 230 μm depth was obtained comprising 10-fold refined dendrites and eutectic carbides as compared with conventional casting. The as plasma treated layer contained supersaturated austenite and “fresh” eutectic “austenite + M 7 C 3 ” crystallized after melting. The latter formed fine networks or “massive” areas comprising fine carbide plates and fibers. A shell/core structure in coarse dendrites was revealed with different contents of Cr and secondary carbides. Post-heat treatment (isothermal holding at 800 °C for 2 h followed by oil quenching) resulted in precipitation of nano-sized secondary carbides in austenite followed by martensite transformation, which significantly increased the microhardness of the melted layer. Phase transformation phenomena and sequences are discussed based on Finite Element/Thermo-Calc modeling, EDS-investigation and hardness profile results. [ABSTRACT FROM AUTHOR]

Low-activation structural materials for fusion applications beyond 700 °C are desired. High-entropy alloys (HEAs) with excellent properties at elevated temperatures are suitable for use in nuclear reactors. A newly developed V 35 Ti 35 Fe 15 Cr 10 Zr 5 HEA was fabricated by vacuum arc melting and the microstructure of as-cast and annealed sample was found to be composed of BCC solid solution phases. It was interesting to find that the yield strength of as-cast V 35 Ti 35 Fe 15 Cr 10 Zr 5 HEA increased with increasing the temperature below 500 °C, and it was much higher than that of vanadium alloy or martensitic steel for fusion reactors in the temperature range of room temperature to 900 °C. At 700 °C, the yield strength of V 35 Ti 35 Fe 15 Cr 10 Zr 5 HEA was about 500 MPa higher than that of vanadium alloy or martensitic steel, showing promise for high temperature applications. V 35 Ti 35 Fe 15 Cr 10 Zr 5 alloy had a relative low ductility below 700 °C, while the alloy exhibited a good ductility above 700 °C. [ABSTRACT FROM AUTHOR]

A successful demonstration of applying integrated strengthening using Hall-Petch strengthening (grains size effect) and precipitation strengthening is shown in the fcc based high entropy alloy (HEA) Al 0.3 CoCrFeNi, leading to quantitative determinations of the Hall-Petch coefficients for both hardness and tensile yield strength, as well as the enhancements in the yield strength from two distinct types of ordered precipitates, L1 2 and B2. An excellent combination of yield strength (~ 490 MPa), ultimate tensile strength (~ 850 MPa), and ductility (~ 45% elongation) was achieved by optimizing and coupling both strengthening mechanisms, resulting from a refined grain size as well as both L1 2 and B2 ordered precipitates. This opens up new avenues for the future development of HEAs, with the appropriate balance of properties required for engineering applications. [ABSTRACT FROM AUTHOR]

A new high entropy alloy (HEA) has been synthesized using a predictive method recently developed. The alloy performance is compared to that of a benchmark commercial alloys (Stellite®6) as wear resistance material for coating automotive engine valves. Using step by step predictive parameters the occurrence of an fcc solid solution with entropy of mixing higher than the conventional limit of 1.5 R (with R the gas constant) was singled out and verified in the FeCoCrNiW 0.3 composition. The as-cast ingot displays W segregation within the fcc grains as revealed by Scanning Electron Microscopy and X-ray Diffraction (XRD) patterns which were fitted by assuming the arc melted alloy contains two solid solutions. The segregation is eliminated by annealing at 1200 °C for 3 h. In these sample a (Co-Fe) 7 W 6 -type phase is found embedded in the solid solution matrix. Slip bands around indentation marks suggest low stacking fault energy of FeCoCrNiW 0.3 . The high entropy alloy (HEA) has been hardened by adding 5 at.% C to form carbides inside the fcc matrix. Conventional hardness, scratch and oxidation resistance tests show that the alloy compares well with Co-based Stellite®6 being the content of the expensive and strategical elements halved with respect to it. [ABSTRACT FROM AUTHOR]

In this study, an age-hardenable Mg–14Gd–0.5Zr (wt.%) alloy was used as a model material to investigate the effects of grain size, texture and density of precipitates on the hardness and 0.2% proof tensile yield stress. Six kinds of samples with different grain size, texture and density of precipitates were prepared by varying the extrusion process and aging treatment. The microstructure and texture of the samples were examined by electron backscatter diffraction and transmission electron microscope. The examination results indicate that 0.2% proof yield stress of the Mg-Gd alloys were largely affected by the grain size and texture, while the hardness of the alloys was predominately controlled by the density of precipitates. This study reveals that the grain size, texture and density of precipitate can have much different influences on the hardness and 0.2% proof yield stress for the Mg-Gd alloys. It raises an important issue about the mechanical-testing standards and product-design guidelines for the age-hardenable magnesium alloys. [ABSTRACT FROM AUTHOR]

[Display omitted] • Lignin is tested using light-microscopy-aided grid nanoindentation. • Micromechanics-based evaluation yields a reliable elastic modulus of 7.1 GPa. • The mechanical properties neither depend on the feedstock nor the extraction process. Lignin, a main component of plants, is produced in large quantities as a by-product of the pulp and papermaking industry. The abundance of this organic polymer makes it an excellent candidate for developing renewable materials such as lignin-based biocomposites. The mechanical properties of lignin, as well as the dependence on the extraction process and feedstock, are, however, still unknown and hamper its utilization. Therefore, five hot-pressed lignins, extracted by different processes from different feedstocks, are tested by means of grid nanoindentation at indentation depths ranging from 150 nm to 1200 nm. Statistical and microstructure-guided evaluation based on microscopy images of the indented areas allows for retrieving reliable indentation properties of the porous lignin, free of indentation size effects. The sought mechanical properties of the solid (pore-free) lignin are back-identified from the strong correlation between the property and the porosity using micromechanics homogenization theory. This correlation reveals that the solid lignin in all tested samples is mechanically similar, despite different chemical structures, with a virtually intrinsic Young's modulus of 7.1 GPa. [ABSTRACT FROM AUTHOR]

[Display omitted] • Co-simulation allowed calibration of a cyclic material model for copper within complex laminated structures without the need for costly measurement equipment. • Nanoindentation on cross-sections enabled the precise determination of the elastic modulus and hardness for the components of complex composites. • Results were interpreted using X-Ray Diffraction and Electron Backscatter Diffraction. • Tabor relation for estimating yield stress was shown not to be applicable for low displacements. Metallic foils are crucial to many applications ranging from printed circuit boards, aviation, aerospace, packaging, photovoltaics to batteries. In these applications they are often part of multifunctional composites, for which mechanical integrity is a prerequisite for the functionality. To ensure precise simulations and lifetime prediction, exact numerical material models are needed. In this work, material parameters of the Lemaitre-Chaboche model were fitted for electrodeposited copper foils. By using nanoindentation and microstructural characterisation, good agreement with literature was achieved. Additionally, it was found that the Tabor rule to estimate yield stress from indentation may not be applicable for metallic foils. [ABSTRACT FROM AUTHOR]

[Display omitted] • An effective design strategy is proposed to improve the toughness and vacuum high-temperature tribological properties of high-entropy carbides by introducing vacancies and Mo. • The fracture toughness of (Zr 0.17 Nb 0.2 Ta 0.2 Mo 0.2 W 0.2)C 0.89 is up to 4.5 ± 0.2 MPa·m1/2 due to the introduction of vacancies. • The (Zr 0.17 Nb 0.2 Ta 0.2 Mo 0.2 W 0.2)C 0.89 presented brilliant friction-reducing and wear-resistant properties, with the lowest friction coefficient (0.31 ± 0.01) and low wear rate (10-6 mm3/Nm) at 900 °C. • The superior tribological properties were attributed to the formation of low-hardness oxidation products containing lubricating phase MoO 3. High-entropy carbides are promising materials as sliding structural components in ultra-high temperature environments due to their good phase stability and excellent mechanical properties. However, the tribological behaviors under coupling conditions of high temperature and vacuum environment have not been deeply evaluated. To fill such a gap, the high-temperature tribological properties of carbon-deficient high-entropy (Zr 0.17 Nb 0.2 Ta 0.2 Mo 0.2 W 0.2)C 0.89 (HEC 0.89) prepared by using five binary carbides (ZrC, NbC, TaC, Mo 2 C, and WC) as starting materials were investigated. The microhardness and fracture toughness of HEC 0.89 were 21.3 ± 0.5 GPa and 4.5 ± 0.2 MPa·m1/2. Most importantly, HEC 0.89 exhibited low wear rate (lower than an order of 10-6 mm3/Nm) under vacuum environments from room temperature (RT) to high temperatures. Moreover, the lowest friction coefficient (0.31 ± 0.01) was obtained at 900 °C, which is attributed to the transferring of films consisting of low hardness oxidation products. These results clearly demonstrate the prospective for the application of high-entropy carbides as sliding parts in high-temperature and vacuum environments. [ABSTRACT FROM AUTHOR]

[Display omitted] • Phase transformation of AISI 304 stainless steel at room temperature caused by plastic deformation using the process of machine hammer peening. • Localized mechanical energy input through machine hammer peening allows spatial influence of magnetic properties. • Non-destructive testing of martensite content using different electromagnetic sensor technologies. • Correlation between magnetic properties and mechanical hardness allows non-destructive hardness measurements. The goal of this work is to establish a correlation between the surface integrity and magnetic properties of stainless steels like AISI 304 (X5CrNi18-10). In metastable austenitic stainless steels, a phase transformation from the austenitic to the martensitic phase can occur even at room temperature. In this work, machine hammer peening (MHP) is used to selectively introduce the activation energy required for martensite formation on discrete areas of the surface. The phase transformation is confirmed by electron back scatter diffraction (EBSD) and micrographs. A correlation between the energy input by MHP, magnetic properties, and surface hardness is established. Using this approach, characterization of the surface integrity by measuring magnetic properties can be achieved. In addition, a novel solution to code and encode information with high information density onto metastable austenitic materials is proposed. [ABSTRACT FROM AUTHOR]

Ni-W/SiC nanocomposite coatings were systematically deposited at varying pulse parameters and subsequently characterized using SEM, XRD, TEM for surface morphology, composition and SiC particle/Ni-W matrix interface phase boundary. In addition, mechanical properties of nanocomposite were also evaluated using nanoindentation. Uniform distribution of submicron SiC particles in nanocrystalline Ni-W alloy coatings was obtained using pulsed electrodeposition. The results indicated increase in SiC content of nanocrystalline Ni-W matrix with increase in pulse frequency and decrease in duty cycle. The incorporation of SiC was attributed to pulse current effect at cathode-solution interface leading to changes in pulsating diffusion layer thickness. A simplified mechanism of composite electrodeposition is proposed. The hardness and modulus of nanocomposite varied with SiC content. The variation in mechanical properties was rationalized based on rule of mixture and inverse Hall-Petch effect. [ABSTRACT FROM AUTHOR]

In order to explore a novel material for thermal barrier coatings (TBCs), the composite ceramic materials of lanthanum zirconate (La 2 Zr 2 O 7 ) and lanthanum phosphate (LaPO 4 ) were prepared by calcining. The phases and micro-structures of La 2 Zr 2 O 7 /LaPO 4 composite ceramic materials were studied by X-ray diffraction (XRD) and scanning electron microscopy (SEM). The properties of La 2 Zr 2 O 7 /LaPO 4 material, such as thermal conductivity, coefficient of thermal expansion (CTE) and mechanical properties of La 2 Zr 2 O 7 /LaPO 4 were investigated using laser flash method, high-temperature dilatometer and micro-hardness test. Based on XRD patterns, the pyrochlore and monazite phases were obtained in La 2 Zr 2 O 7 /LaPO 4 composite ceramic material without any chemical reaction. According to SEM morphology, the La 2 Zr 2 O 7 was closely near to LaPO 4 along with a lot of pores, it might cause the decrease of thermal conductivity. The thermal conductivities of composite ceramics were similar to that of La 2 Zr 2 O 7 . The CTE of them were about 10 × 10 − 6 K − 1 , which was close to the value of LaPO 4 . Because of doping LaPO 4 , hardness and Young's modulus of samples were lower than that of La 2 Zr 2 O 7 . The studies revealed that the La 2 Zr 2 O 7 /LaPO 4 composite ceramics had good mechanical and thermal physical properties and could be applied as new candidate materials for TBCs in the future. [ABSTRACT FROM AUTHOR]

Laser shock peening (LSP) with different cycles was performed on the Ti-based bulk metallic glasses (BMGs). The sub-surface residual stress of the LSPed specimens was measured by high-energy X-ray diffraction (HEXRD) and the near-surface residual stress was measured by scanning electron microscope/focused ion beam (SEM/FIB) instrument. The sub-surface residual stress in the LSP impact direction (about − 170 MPa) is much lower than that perpendicular to the impact direction (about − 350 MPa), exhibiting anisotropy. The depth of the compressive stress zone increases from 400 μm to 500 μm with increasing LSP cycles. The highest near-surface residual stress is about − 750 MPa. LSP caused the free volume to increase and the maximum increase appeared after the first LSP process. Compared with the hardness (567 ± 7 HV) of the as-cast BMG, the hardness (590 ± 9 HV) on the shocked surface shows a hardening effect due to the hardening mechanism of compressive residual stress; and the hardness (420 ± 9 HV) on the longitudinal section shows a softening effect due to the softening mechanism of free volume. [ABSTRACT FROM AUTHOR]

Nanocrystalline (NC) Ni 3 Al thin films have poor mechanical properties at a high temperature and in order to improve the thermal performance, it is necessary to develop novel micro- or nanostructures that endow the coatings with both high thermal stability and hardness. In this work, Ni 3 Al thin films with different W concentrations up to 12.5 at% are deposited on Si/SiO 2 substrates by magnetron sputtering and then vacuum-annealed at 500 °C and 700 °C. Addition of W to the nanostructured Ni 3 Al thin films leads to grain refinement and high thermal stability. The hardness ( H ) of the film with 12.5 at% W annealed at 700 °C increases by 355% compared to pure Ni 3 Al. X-ray diffraction and transmission electron microscopy reveal non-equilibrium phases such as the amorphous phase and supersaturation solid solution in the films annealed at 500 °C. After annealing at 700 °C, the α-W phase precipitated in the fine nanocrystalline state plays a crucial role in the high thermal stability of the nano-grains as well as enhanced hardness. The results suggest that these durable Ni-based coatings are suitable for applications at high temperature. [ABSTRACT FROM AUTHOR]

Cr12MoV has wide applications in the molds and dies industry. However, it is also a hard-to-machining material due to its high mechanical strength and hardness. Area ablation of Cr12MoV cold-work mold steel was carried out using a picosecond (ps) pulse Nd:YVO 4 laser. The effects of laser fluence and wavelength on the ablation rate and machining quality were investigated with wavelengths of 1064 nm, 532 nm and 355 nm. The experimental results indicate a logarithmic increase of the ablation rate to a maximum value of ~ 41 nm/pulse with the increase of laser fluence using the wavelengths of 1064 nm and 355 nm. For the wavelength of 532 nm, an ablation rate of ~ 33 nm/pulse is achieved at low laser fluence of 8.28 J/cm 2 , then increases logarithmically into about 54 nm/pulse at 25.10 J/cm 2 , and then decreases steeply into almost zero as the laser fluence increases above 25.10 J/cm 2 . For the three laser wavelengths, different pore sizes were observed in the laser ablation region. The surface roughness increases exponentially with the increase of the laser fluence. The influence mechanisms of laser fluence and wavelength on the laser ablation rate and machining quality were systematically analyzed and discussed in this paper. [ABSTRACT FROM AUTHOR]

Cu/C composites were prepared from Cu and graphite by accumulative roll-bonding (ARB) up to 30 cycles ( N ) with a 50% thickness reduction per cycle at room temperature. The microstructure and properties of the Cu/C composites were investigated. Results showed that ARB can remarkably decrease the size of graphite and improve the dispersion of graphite in the Cu matrix. Moreover, significant thickness reduction (down to ~ 5 graphene layers) of the graphite was found in the Cu/C composites fabricated by ARB. The microhardness of the Cu/C composites increases with increasing N and is ~ 3.3 times that of pure Cu for N = 30. The electrical conductivity of the Cu/C composites decreases slightly with increasing N , with a minimum of ~ 90% IACS for N = 30. Our study indicated that ARB can be an effective method for fabrication of Cu/C composites from Cu and graphite with a combination of hardness and electrical conductivity better than or as good as that of carbon nanotube or graphene reinforced Cu matrix composites as reported. [ABSTRACT FROM AUTHOR]

Oxide dispersion strengthened (ODS) austenitic steel (Fe-16.8Cr-22Ni-2W-2.4Mo-1.5Mn-0.62Si-0.15La-0.2Ti + 0.35Y 2 O 3 , wt%) was prepared by mechanical alloying and consolidated by hot extrusion followed by solutionization at 1150 °C for 1 h. The composition of this steel is designed to suppress the formation of deleterious delta (δ-) ferrite and sigma (σ-) FeCr phases, which reduces the life the materials. Various microscopic, spectroscopic and diffraction techniques were employed to study the hierarchical microstructural features of this alloy. X-ray diffraction studies confirm the austenitic phase and no traces of δ-ferrite phase were observed in as-extruded and solutionized conditions. The solutionized austenitic ODS steel exhibited ultra-fine grain structure having mean sizes of 280 ± 5 and 440 ± 9 nm in transverse and longitudinal sections of the bar, respectively. Evenly dispersed high density of Y-Ti-O nano-oxides with a mean size of 9 nm was achieved along with low fractions of TiC and La rich Y 2 Si 2 O 7 . The crystal structure of Y-Ti-O nano-oxides was determined by combining HR-TEM and FFT techniques and was found to be pyrochlore Y 2 Ti 2 O 7 . These dispersoids and ultra-fine grain structure of austenitic steel contribute to an enhanced hardness of 346 ± 25 HV. [ABSTRACT FROM AUTHOR]

In the present paper, to understand the nature of newly designed Ni43Ti4Al2Nb2Hf alloys in the case of avoiding shape memory, TEM and HREM were used to reveal the precipitation type, phase composition and its relationship with the hardness. Cyclic tensile loading-unloading test is also carried out to study the deformation behavior. It is observed that a new phase with the approximate composition of Ti 36 ± 2 -Ni 34 ± 2 -Nb 20 ± 2 -Al 8 ± 1 -Hf 2 ± 0.5 precipitates in the directional solidified Ni43Ti4Al2Nb2Hf alloy, which is identified to be the base-centred monoclinic lattice with lattice parameters a = 0.987 nm, b = 0.504 nm, c = 1.172 nm, α = γ = 90°, β = 130.18°, and space group C2/c. The hardness of the Ni36Ti20Nb8Al2Hf alloy with same composition to the new phase is more than 810 HV, nearly twice of that of the Ni43Ti4Al2Nb2Hf alloy, which confirms the strengthening effect of the new phase. In addition, the cyclic loading results indicate that the linear recoverable strain is more than 3%, which exhibits the significantly enhanced load capability of this alloy. [ABSTRACT FROM AUTHOR]

Nb-18Si-24Ti-2Cr-2Al-2Hf (at%) alloy was fabricated by selective laser melting (SLM). The microstructure, hardness and oxidation behavior of Nb-Si based alloy via SLM were investigated. Results showed that the relative density of SLM alloy under the optimized processing parameters was 98.27%. The as-built alloy consisted of Nb solid solution (Nbss), αNb 5 Si 3 , βNb 5 Si 3 and Nb 3 Si. Sphere shaped Nbss phases with a maximum diameter of 300 nm were obtained. Between the neighbouring Nbss phases distributed the strip shaped α/β Nb 5 Si 3 phases. After heat treatment at 1500 °C for 4 h, the Nbss phases interconnected to form a continuous matrix with discontinuous αNb 5 Si 3 phases. The average hardness of the SLM parts decreased from 810HV 0.1 to 542HV 0.1 after heat treatment. Compared with the oxide scale on arc-melted alloy, oxide scale formed on SLM-processed after oxidation at 1300 °C for 0.5 h was more compact with fewer holes, combined with the formation of a more continuous SiO 2 layer at the initial oxidation stage. A layer-structured oxide scale model was presented to describe the high-temperature oxidation behavior of Nb-Si based alloy processed by SLM. [ABSTRACT FROM AUTHOR]

Lightweight Al 2 NbTi 3 V 2 Zr alloy was fabricated through mechanical milling and vacuum hot pressing. The effects of milling on the microstructure, phase evolution, and hardness of the fabricated alloy were investigated. High-energy (HE) milling decreased the size of crystalline grains and activated the powders for subsequent sintering. HE-annealed powders at above 900 °C and all sintered bulks consisted of body-centered cubic (BCC) and intermetallics α and β. Low-energy (LE) milling only provided homogeneity to the powders. LE bulks exhibited a microstructure similar to that of HE bulks at 1450 °C–1550 °C. The hardness of the HE bulk was higher than that of the LE bulk and exhibited a peak value of 781 HV at 1250 °C. All Al 2 NbTi 3 V 2 Zr bulks possessed low density ranging from 5.05 g/cm 3 to 5.25 g/cm 3 . Two empirical equations for hardness of the bulks were proposed for the BCC matrix bulks and simple cubic matrix bulks respectively and the estimated results are consistent with the experimental measurements. [ABSTRACT FROM AUTHOR]

Highly wear-resistant alloys are important in many engineering and biomedical applications. In this research, a multi-phase quasicrystal-based alloy was developed using a rapid arc-melting technique. The alloy contains three characteristic phases, hard λ-Al 13 Fe 4 , quasicrystal icosahedral (i-phase), and ductile τ-AlCu. The Vickers micro hardness of each was 828, 795, and 552, respectively, with an overall hardness of 334 (HR15T). Due to the co-existence of these three phases, this alloy exhibits both hardness and ductility. As such, the new material has favorable wear and crack resistance. The approaches used in this study are beneficial for the future design and development of this class of quasicrystalline alloys. [ABSTRACT FROM AUTHOR]

The present study was performed on 356 and 413 alloys containing various amounts of hydrogen (H 2 ), titanium diboride (TiB 2 ), and strontium (Sr). The results show that the eutectic silicon particles in non-modified alloys undergo coarsening during the solutionizing treatment. High energy levels are obtained when the alloy is degassed, Sr-modified, and grain refined. Precipitation of Mg 2 Si phase particles in 356 alloys is more effective as a hardening agent than the Al 2 Cu phase precipitated in the 413 alloy which contributes to the alloy strength/hardness. The increased Si content in non-modified 413 alloys accelerates crack initiation and propagation, leading to low toughness values. Modifying the 413 alloys with 200 ppm Sr results in a more even distribution of the spheroidized eutectic Si particles and hence better the alloy toughness. Exceeding the required amount of Ti-containing grain refiner may result in the introduction of a large amount of brittle Al 3 Ti platelets that would reduce the alloy toughness. [ABSTRACT FROM AUTHOR]

The current study proposes warm laser peening without coating process utilizing decarburized surface as the protective ablation layer and is directly intended towards the experimental evolution of existing laser shock peening technology. The interlath-retained austenites are transformed into martensites during warm laser peening. Also, the depth-wise compressive residual stress and its thermal relaxation behavior are comparatively prevailing. The scanning and transmission electron microscopic analysis identify the severe plastic deformation features of microstructures. So, the grain refinement and pinning force mechanisms on the mechanical properties are recognized. Further, the micro and nano-hardness studies provide a significant improvement in the surface and sub-surface mechanical properties. Moreover, the optimized fatigue life of low-alloy steel is achieved through the thermal engineering process. The present work increased the fatigue life of the specimen by 26 times and it is effectively repairing the partially pre-fatigued specimen. [ABSTRACT FROM AUTHOR]

[Display omitted] • The intensified intrinsic heat treatment promotes the abnormal δ phase precipitation. • Laves and δ are heterogeneously distributed within the as-built specimens. • Longer interlayer dwell time was introduced to uniform the distribution of precipitation. • Hardness fluctuation within the as-built specimens was decreased by 47%. The effect of intrinsic heat treatment (IHT) induced by cyclic heat input in laser additive manufacturing (LAM) has been receiving increasing attention in recent years. Herein, the feasibility of tailoring the microstructure and mechanical properties of Inconel 625 alloy to improve material properties and help achieve part quality consistency by controlling IHT in directed energy deposition (DED) is demonstrated. In this study, thermal monitoring was used to obtain thermal histories of as-built specimens to reveal the differences in thermal characteristics under different IHT. The results show that the variation of IHT has an important effect on the primary dendrite arm spacing (PDAS), the temperature and cooling rate of the molten pool, the morphology and content of Laves, and can initiate unusual δ precipitation in the interdendritic region which may be related to the dissolution of Laves. And this time-position-dependent IHT effect results in a hardness fluctuation of about 23.6 % in the bottom and top of the as-built specimen with a dwell time of 1 s, while the hardness is relatively uniform in the specimen with a dwell time of 10 s. Furthermore, by simulating the IHT variation process, its effect on precipitate and hardness was further confirmed. [ABSTRACT FROM AUTHOR]

[Display omitted] • Design of a new technique based on planar-flow melt-spinning for the fabrication of metallic glass microfibers. • The new technique is based on wetting and formation of thin film on rotating copper wheel followed by simultaneous rupture of the film into microfibers in the range of 1–20 µm. • The nature of the new technique makes it possible to fabricate fully amorphous structure from alloy compositions which are not designed for metallic glass formation. • We have shown and confirmed the formation of fully amorphous structure in µm-range, from Ti-stabilized 316 stainless steel. The amorphous structure is confirmed by XRD, DTA, TEM. • The hardness of the as-purchased stainless steel increased from ∼ 2.5 to ∼ 8.2 GPa after formation of the amorphous structure. • The subsequent stepwise heat-treatment on the amorphous stainless steel creates adjacent nanostructured and amorphous grains, observed by TEM. • The heat-treated stainless steel shows an even further increase in hardness to ∼ 14.2 Gpa. • We believe that both the confinement of dislocation movement in the nanocrystalline grains as well as the absence of dislocations in the amorphous grains contribute to this tremendous increase of hardness in heat-treated stainless steel. The high passivation capacity of austenitic stainless steel results in their excellent corrosion resistance. There are many ways to improve the hardness of austenitic stainless steel such as cold rolling or grain refinement. Herein, we explore the possibility of improving the hardness of AISI316-Ti stainless steel by generating an amorphous-nanocrystalline microstructure. First, we have utilized our modified melt-spinning technique to fabricate AISI316-Ti stainless steel microfibers with a fully amorphous structure. Formation of a fully amorphous structure was confirmed by using X-ray diffraction (XRD), differential thermal analysis (DTA), and transmission electron microscopy (TEM). Thermal analysis revealed a glass transition temperature of 437˚C followed by a crystallization peak of 573˚C. Nanoindentation analysis showed a fourfold increase of hardness from the initial value of ≈2.5 ± 0.1 GPa the starting AISI316-Ti stainless steel rod to the hardness of ≈8.2 ± 0.5 GPa for the amorphous AISI316-Ti structure. Further step-size heat treatment on melt-spun (amorphous) stainless steel microfibers generated a microstructure compromising adjacent nanocrystalline and amorphous grains as observed by TEM. Nanoindentation analysis of those fibers has shown an even greater increase in hardness, reaching an average value of ≈14.2 ± 1.0 GPa. We believe that both the confinement of dislocation movement in the nanocrystalline grains as well as the absence of dislocations in the amorphous grains contribute to this tremendous increase of hardness in stainless steel. [ABSTRACT FROM AUTHOR]

[Display omitted] • When the thickness of AlN-Ni layer is 2.4 nm, the TiN/AlN-Ni film behaves super-hardness and high toughness. • The superhard effect is mainly caused by Koehler strengthening and alternating stress hardening. • The formation of coherent interface and the AlN phase transformation are the key reasons for high toughness. A series of TiN/AlN-Ni multilayer films with different modulation layer thicknesses were prepared by magnetron sputtering. Their microstructures and mechanical properties were characterized by X-ray diffraction (XRD), scanning electron microscopy (SEM), and high-resolution transmission electron microscopy (HRTEM). Therein, fracture toughness of multilayer films was determined by indentation method. The hardness and elastic modulus of all multilayers are greatly improved by introducing an AlN-Ni modulation layer. When the modulation-layer thickness is 2.4 nm, and the hardness and elastic modulus are the highest at the value of 39 GPa and 447 GPa, respectively, which is ascribed to Koehler strengthening and alternating stress hardening. Meanwhile the fracture toughness reaches the maximum, namely 5.49 MPa·m1/2. It is attributed to the indentation-induced phase transformation of c-AlN to w-AlN and the formation of a good coherent interface. With further increasing the thickness of the AlN-Ni modulation layer, the multilayer film gradually becomes an amorphous structure, resulting in the decrease of hardness and toughness. [ABSTRACT FROM AUTHOR]

[Display omitted] • A new framework of design of experiments (DOE) informed deep learning (DL) model is developed for modeling of directed energy deposition (DED) process with a small-size experimental dataset. • The developed DOE-informed DL model can accurately predict the cross-section dilution shape (including depth) and the bead geometrical characteristics (including width, height, area, and wetting angle), porosity, and hardness at any position of single-track deposition. • Even though only the single-track deposition dataset is applied in this study, the DOE-informed DL model can be extended to multi-layer deposition seamlessly to solve data generation challenges in DED process development in future work. In order to address the high throughput data generation challenges in the directed energy deposition (DED) process development, a design of experiments (DOE) informed deep learning (DL) model is developed for modeling of laser powder-based DED process. A small-size experimental dataset is obtained according to DOE, by which a large-size dataset is augmented via the DOE regression model and then used to pre-train the DL model. A subset of experimental data is employed to fine-tune the DL model. The presently developed DOE-informed DL model is validated via single-track deposition of stainless steel 316L, in which the cross-section dilution shape (including depth) and the geometrical characteristics of beads, including the width, height, area, and wetting angle are predicted accurately. The prediction of the porosity and hardness are acceptable for single-track deposition, since variations of both the experimental porosity (from 0.04 % to 0.30 %) and hardness (from 168 HV to 182 HV) are quite small for the single-track deposition, especially predicted ranges for the porosity (from 0.05 % to 0.25 %) and hardness (from 170 HV to 180 HV) are the subset of the experimental results. The DOE-informed DL model developed in this study is based on a single-track deposition dataset; in future work, the DOE-informed DL model will be extended to multi-layer deposition. [ABSTRACT FROM AUTHOR]

Multilayer architecture based on CrAlN coatings to improve their properties attracts great attention. Here, the structure, mechanical and thermal properties of CrAlN/ZrN multilayer coatings with bilayer periods of ~ 5 and 9 nm are investigated. Decreasing bilayer period of CrAlN/ZrN coating from 9 to 5 nm results in a transformation of interfacial structure between CrAlN and ZrN sublayers from nonepitaxial to local epitaxial interfaces, and thereby has a positive effect on the hardness, adhesion strength, thermal stability and oxidation resistance. Additionally, a layer by layer oxidation behavior of CrAlN/ZrN coatings leads to the formation of lamellar oxide scale. [ABSTRACT FROM AUTHOR]

Selective laser melting (SLM), an additive manufacturing technology, was utilized to process TiC/316L nanocomposite systems with different starting TiC particle sizes and volume contents. The influence of the starting TiC particle size and volume content on the constitutional phases, microstructural features, and mechanical properties of the SLM-processed nanocomposite parts was investigated. The densification behavior was controlled by both the starting TiC content and the particle size; the densification level was enhanced with the use of fine starting TiC particles owing to the improvement of the reinforcement–matrix wettability. In general, by increasing the volume content of the TiC, the hardness increased and the coefficient of friction (COF) and wear rate deceased owing to the combined effects of grain refinement and grain-boundary strengthening. However, in contrast to the starting coarse TiC particles, the SLM-part processed with the starting fine TiC particles shows better wear resistance, in particular at a 10–15% TiC content, owing to improved TiC dispersion throughout the matrix and increased density. [ABSTRACT FROM AUTHOR]

Analysis of the effect of microstructure refinement, water quenching, natural ageing as well as T5 and T6 tempers on macro-hardness development of the hypereutectic HPDC Al–Si based alloy was performed. Duration of casting holding at room temperature after its removal from the die, and prior to subsequent temper operation had a measurable effect on casting macro-hardness. Such finding underlined the need for tighter control of parts handling between casting and heat treatment operations. Water quenching after casting de-molding operation increased alloy macro-hardness in naturally aged as well as T5 temper conditions but did not have any effect on macro-hardness after T6 treatment. T5 temper carried out after casting de-molding and water quenching from 380 °C enabled on average approximately 9 to 19% macro-hardness increase as compared to the T1 condition. Microstructure refinement had a minor effect on macro-hardness increase but the measurements of the α-Al matrix micro-hardness needed to be used to demonstrate this effect. Compared with T6, the T5 temper offered up to approximately 20 to 60% shorter process duration and could offer potential cost reduction gains achieved at the expense of lower macro-hardness. Microstructure refinement did not have the effect on T6 casting macro-hardness. [ABSTRACT FROM AUTHOR]

Authors investigated mechanical properties of microcrystalline Fe 89−x Hf 4 Ta 1 Cu 1 Gd 1 Si x B 4 (x = 0–15) and Fe 74 Hf 4 Ta 1 Cu 1 Gd 1 La y Si 15−y B 4 (y = 7) alloys obtained by copper mold injection casting to a form of rods, 3 mm in diameter. Structure of the samples was analyzed by Cu K- α powder X-ray diffractometry and the unit cell parameters of identified h-Fe 2 Hf 0.8 Ta 0.2 (C14 Laves), fcc-Fe 16 Hf 6 Si 7 (D8 a ) and bcc-Fe phases were calculated. The study revealed that ascending Si content leads to reduction in values of both unit cell parameters of C14 phase in the alloys studied while causes the expansion of D8 a lattice; decrease in secondary dendrite arm spacing in the middle of the rods; stepwise improvement of yield and compressive strength at the expense of plastic deformation region, what was attributed to the precipitation of C14 Laves/D8 a in the interdendritic regions of bcc-Fe; decrease in flexural strength with no effect on deflection-at-yield and exponential increase in hardness of the studied alloys. There is also clear correlation between unit cell volume of fcc-Fe 16 Hf 6 Si 7 phase, yield and compressive strength on Si content. For the alloys with x = 0–13, relation between yield strength and Vickers hardness was described with logarithmic function. It was found, that the lattice expansion of bcc-Fe and, in lesser extent, C14 Laves phase is correlated with the value of bending modulus in the whole composition range. [ABSTRACT FROM AUTHOR]

Laser surface hardening is a promising technology to improve wear and fatigue properties of steel surfaces. When the dimensions of the surface to be treated are larger than the cross section of the laser beam several overlapped tracks are needed, and the distance between consecutive tracks becomes a fundamental design parameter. This work aims to optimize that parameter with the purpose of fulfilling a set of initial requirements for the process. A laser hardening temperatures/oxidation coupled model available in the literature is applied for the first time to the case of an overlapping process, extending its capabilities to take into account the tempering of the second track over the martensite of the first one. This model in conjunction with a convenient geometrical characterization of the heat affected zone enables a design strategy to be implemented which, using metallurgical and hardness maps, has the capability of attending different criteria. All the conditions proposed in the design of a suitable overlapping distance have been reproduced empirically for the case of the 42CrMo4 steel, and a comparison of hardness has been carried out, showing a good degree of agreement. [ABSTRACT FROM AUTHOR]

A linear single variable model for describing precipitation heat treated Al-Zn-Mg-Cu aluminium alloy hardness and yield strength based on precipitate compositions was proposed. A concept composition model was developed based on the major alloying elements and the strengthening precipitate compositions, for the precipitation heat treatment condition. A Refined composition model was subsequently developed to account for the effect of minor alloying (Mn) and impurity elements (Fe, Si). Macro segregation of alloying elements had a significant effect on the results of the Refined composition model. Mechanical properties varied according to a simple linear relationship with the atomic fraction of the strengthening precipitate. The T6 and T73 hardness, and T6 yield strength were algebraically expressed, with linear relationships. The model describes existing yield strength data for Al-Zn-Mg-Cu aluminium alloys. The Refined composition model was also valid for predicting yield strengths of Al-Zn-Mg-Cu-Zr aluminium alloys in the T6 condition. [ABSTRACT FROM AUTHOR]

Additive manufacturing (AM) has a strong potential for the formation of a new class of multifunctional nanocomposites. In this study, nanocomposite feedstock powders were prepared by a mechanical alloying method based on high-energy ball milling. The evolution of constitutional phases and microstructural features of the milled powders was investigated as a function of milling time. The results showed that the milled powder particles experienced significant cold-welding during the entire milling time, with a wide size distribution. Selective laser melting (SLM), a promising AM fabrication technique, was applied to produce nanoscale 15% (by volume) TiC-reinforced H13 steel matrix nanocomposites. After SLM, uniformly dispersed nanoscale TiC particles with a mean particle size of 50 nm were obtained and a fine heterogeneous structure was observed. Relative to the unreinforced H13 steel part, the TiC/H13 steel nanocomposite parts exhibited higher hardness and elastic modulus, along with lower friction and a lower wear rate; these improvements are attributed to the combined effects of grain refinement and grain boundary strengthening. [ABSTRACT FROM AUTHOR]

In the present study, powder metallurgy processed unmilled AlMg5 (AlMg5-UM), milled AlMg5 (AlMg5-M), and milled AlMg5–0.4 vol.% Al 2 O 3 (AlMg5–0.4Al 2 O 3 ) nanocomposite were successfully spark plasma sintered at 550 °C. The microstructural analysis of spark plasma sintered AlMg5-UM revealed equi-axed grains with average size of 20 ± 5 μm. The microstructural analysis of spark plasma sintered AlMg5-M and AlMg5–0.4Al 2 O 3 revealed a bimodal grain structure with both fine-coarse grains of size 700 nm–8 μm and 300 nm–8 μm, respectively. The spark plasma sintered AlMg5-UM exhibited a yield strength (YS) of 132 ± 3 MPa, ultimate tensile strength (UTS) of 296 ± 2 MPa and % elongation (% El) of 22 ± 2 comparable to the conventional Al 5083 alloy — O temper (YS of 145 MPa, UTS of 281 MPa and % El of 16). The spark plasma sintered AlMg5-M and AlMg5–0.4Al 2 O 3 exhibited YS of 242 ± 9 MPa and 274 ± 5 MPa, UTS of 376 ± 4 MPa and 417 ± 8 MPa and % El of 19 ± 1 and 10 ± 1, respectively. The lower strength (YS and UTS) of AlMg5-UM can be ascribed to its coarse grains. Among the milled samples, the AlMg5–0.4Al 2 O 3 composite exhibited high strength and it can be ascribed to its fine grain size (Hall–Petch effect), higher dislocation density and Orowan strengthening effect due to Al 2 O 3 reinforcements. [ABSTRACT FROM AUTHOR]

Friction stitch welding of S355 steel was conducted under wet conditions to study the bonding quality. The effects of plug material, joint design, and welding variables on the weld defects, microstructural characteristics, hardness levels, and tensile properties were investigated. The underwater stitch welding performed with a S355 steel plug exhibited visible bonding defects at the weld interface, while the weld with LF2 as the plug material yielded a qualified joint without cracks or discontinuities, provided the plug and hole geometries were well-designed. The LF2-plug-stitch weld contained more upper bainite and fewer lath martensite grains, which was consistent with the substantially decreased hardness values in the weld metal. The joint was designed with large initial contact area and gap between the plug and hole, so a higher amount of heat was generated when welding was started. Further, the welding time was extended from 11 to 16 s, resulting in a larger heat affected zone and the flow of the plasticized (or squeezed) material was improved too. Stitch welds realized with a 40 kN forging force exhibited better ultimate tensile strength and elongation than those with a 35 kN forging force, when the other conditions were kept constant. [ABSTRACT FROM AUTHOR]

The present study was carried out on two Al-Si alloys viz. B319.2 and A390.1, in order to determine their impact toughness under certain test conditions. The results show that due to the presence of mixed types of silicon in the A390.1 alloy, it is not possible to quantify their sizes. Moreover, due to the difference in the densities of Si and Al, the primary Si particles tend to segregate in certain areas, leading to an inhomogeneous distribution of these particles, and, in turn, a marked deviation in the alloy toughness from one sample to another. The presence of Fe-based intermetallics was shown to have lowered the impact energy values of the B319.2 alloy (with 7% Si) in the as-cast condition to reach those values obtained in the A390.1 alloy (with 17% Si). The B319.2 alloy demonstrated a noticeable response to the applied heat treatment. The A390.1 alloy, however, did not exhibit such a variation in toughness as a function of test condition. This was primarily attributed to the presence of a large number of coarse primary Si. [ABSTRACT FROM AUTHOR]

There presently exists a demand for development of magnesium (Mg) alloys for wrought applications. In this study, alloying additions of Zn, Ca, Zr, Gd and Sr to Mg were made in binary, ternary and quaternary combinations up to a maximum total alloy loading ~ 3 wt.%, and thus termed dilute. Such dilute alloys were studied for the purposes of potential sheet applications. The corrosion of a total of 53 custom alloys was studied in conjunction with microhardness. The results reveal that hardness increased with total alloy loading, whilst the corrosion rates did not show any clear relationship with alloy loading. Corrosion of the tested alloys was instead very sensitive to both the type and amount of the unique alloying addition. This indicates that the optimisation of properties requires a detailed knowledge of the electrochemical influence of unique alloying additions. The work contributes to an understanding of compositional effects on the corrosion of Mg, and can be exploited in prediction of corrosion resistance of existing and future Mg alloys. [ABSTRACT FROM AUTHOR]

In this paper hybrid welding of the annealed AA5754 alloy was studied and the role of post weld heat treatment (PWHT) on microstructure and mechanical properties was investigated. The microstructure and hardness of the base material and welds were analyzed. Due to the segregation, the lowest microhardness value was observed at the welding centerline. High microhardness was registered in a narrow zone at the interface between the fusion zone and the heat affected zone where the welding cycle promotes both the strengthening by Mg solid solution and the lowest grain size. The hardness of the heat affected zone was higher than that of the base material due to dissolution of soluble particles (Mg2Si and Mg2Al3). PWHT at 350 °C increased the microhardness in the fusion zone and the tensile strength with respect to the untreated joint, whereas the strain at fracture was similar showing that the fracture was promoted mainly by the presence of porosity, coarse grain size and insoluble segregated second phases. [ABSTRACT FROM AUTHOR]

Bulk Fe-N alloys were fabricated using ultra-fine ε-Fe3N powder by spark plasma sintering (SPS) at 600 °C, 650 °C, 700 °C, and 750 °C. The sintering temperatures were varied over wide ranges and the impact of such variations on sintered specimens was investigated through the characterization of their microstructures, chemical compositions, hardness, densities, compressive properties, and magnetic properties. The results indicate that γ′-Fe4N and α-(Fe,N) (Fe-N solid solution) are the major phases of sintered specimens and the nitrogen concentration can significantly reduce with the sintering temperature increasing. The Fe-N phase transformation behavior during sintering process influences the instantaneous density, microstructure, and properties. The γ′-Fe4N and α-(Fe,N) formed an homogeneous multiphase structure in the specimen sintered at 700 °C and this structure shows excellent compressive properties. Specimens sintered at 750 °C possess higher toughness, larger saturation magnetization, lower coercivity, and less remanence ratio. These findings indicate a certain nitrogen concentration bulk Fe-N alloy with good performance is attainable via SPS. [ABSTRACT FROM AUTHOR]

This paper aimed to study the influence of blast furnace slags on mechanical, thermal and tribological properties of friction materials elaborated by the dry heat-press molding method. Physical, mechanical and thermal properties were analyzed and tribological behavior was studied for varying the extent of doping (13–43 wt.%). The results indicate that the hardness decreases from 63.6 HRL to 57.0 HRL with increasing slag content from 0 to 43 wt.%. But density is opposite for the doped samples. The impact strength gradually increases from 3.59 kJ/m 2 to 3.70 kJ/m 2 when the content of slag increases from 0 to 43 wt.%. Doping was also found to increase the friction coefficients but decrease wear rates, mass-loss and heat release. The sample S 4 has a more superior and stable friction coefficient than others because of the transfer layers formed on the surface of friction materials. [ABSTRACT FROM AUTHOR]

In recent years, the growing environmental awareness has led to the development of energy-efficient products, for example by the replacement of steel as construction material by aluminium to save weight and thus increase the energy-efficiency of mobile systems. However, to address the energy-efficiency of a product holistically, the energy consumption of the production process also has to be considered. For the anodic oxidation process of the AlMgSi1 aluminium alloy, the influence of the sulphuric acid concentration, the glycolic acid concentration, the electrolyte temperature and current density on coating thickness, hardness, ductility and wear resistance (scratch test), as well as on the consumption of electrical energy and process costs for the oxide coating formation are investigated using a design of experiments (DOE). An analysis of variance (ANOVA) is conducted to assess the significance of the parameters for the coating and process properties. For the considered range of the process parameters a significant enhancement of thickness, hardness and wear resistance of the coatings alters also energy consumption during anodic oxidation and process costs, which are assessed by material flow cost accounting (MFCA). [ABSTRACT FROM AUTHOR]