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[Display omitted] • Adding nanoparticles boosts ARMOX 500 T's weld heat-affected zone hardness by up to 16.6 % and 5.28 %. • Among the three applied nanoparticles, tungsten carbide 8% exhibited the highest hardening effect. • Nanoparticle flux induces arc plasma contraction and deflection, refining microstructure. Given the direct correlation between the hardness of high-hardness armor (HHA) steel and its ballistic performance, mitigating softening in the heat-affected zone (HAZ) becomes essential. In this study, welding was performed using a nanoparticle flux composed of Tungsten Carbide (WC), Titanium Carbide (TiC), Silicon Carbide (SiC) nanoparticles, and ethanol. Subsequently, the shape and hardness distribution of each weld bead were comprehensively analyzed. The analysis revealed an increase in penetration depth in the order of 0.37 mm for WC 8 %, 0.31 mm for SiC 8 %, and 0.12 mm for TiC 2 %. Furthermore, the hardness evaluation results demonstrated a significant improvement at the fusion line (FL) when nanoparticle flux was utilized. Specifically, hardness values of 654.0 HV and 590.4 HV were observed at 8 % WC and 8 % SiC, respectively, representing increases of 16.6 % and 5.28 % compared to the absence of nanoparticle flux. Additionally, further investigations were conducted to elucidate the mechanism behind the improvement in hardness. This experimental evidence confirms the effectiveness of incorporating WC 8 % and SiC 8 % nanoparticles into the welding process of ARMOX 500 T in preventing hardness degradation due to softening. [ABSTRACT FROM AUTHOR]

[Display omitted] • We demonstrate a new way of inducing local recrystallization, using a selective laser-based heat treatment technique. • Synchrotron X-ray diffraction investigates recrystallization kinetics in cold-rolled 316L steel after such laser treatments. • The evolution of full width at half maximum of diffraction peaks can be directly correlated to the successive recrystallization stages. • Recrystallization stages were characterized by Transmission Electron Microscopy and Scanning Electron Microscopy. Laser based heat treatments have multiple applications for local tuning of microstructures. They are particularly relevant in the context of laser-based additive manufacturing (LAM), in order to relieve residual stresses or introduce equiaxed structures through recrystallization. In 316L, high stored energy inherited from the high cooling rates of laser processing creates strong crystallographic textures and stable cellular walls, which challenges the possibility of inducing fast recrystallization. In a first step, we perform here a laser heat treatment on a highly deformed 316L steel, and show that in-situ X-ray Diffraction (XRD) is a viable tool for the monitoring of fast recrystallization. The evolution of Bragg peak width over time is connected to the evolution of dislocation density and grain size, thanks to Electron Back-Scattered Diffraction (EBSD) and Transmission Electron Microscopy (TEM) characterization. X-ray signals are shown to reveal different stages of recrystallization, in particular the development of dislocation cells and the onset of nucleation. This study also demonstrates how local heat sources such as lasers may help designing composite-like materials for grain size, texture and hardness optimization. [ABSTRACT FROM AUTHOR]

[Display omitted] • TiN assisted in the formation of a nitride-dislocation network and improved the mechanical properties of NiTi. • Nitrogen segregation leads to grain refinement, generation of high-angle grain boundaries, and loss of shape memory effect. • A low-temperature aging process recovered the shape memory effect, leading to a high hardness of ∼4.0 GPa and a low reduced elastic modulus of ∼57.5 GPa. The role of the protective gases in laser-based powder bed fusion (L-PBF) is mainly to avoid the oxidation of metals during the melting and solidification process. However, the gaseous environment can also interact with metals, and result in changes in microstructure and properties. In a NiTi alloy, we found the L-PBF processes in the N 2 gaseous environment can induce TiN particles and facilitate the formation of a precipitate-dislocation network and therefore improve mechanical properties. Nitrogen segregation also led to grain refinement and the generation of high-angle grain boundaries. The as-printed NiTi in N 2 loses its shape memory effect, however, an aging process at 500 °C resulted in unchanged grain size, parallel arrays of Ni 4 Ti 3 precipitates around TiN, and a recovery of shape memory effect. The optimization of microstructure finally resulted in a high hardness of ∼4.0 GPa and a low reduced elastic modulus of ∼57.5 GPa. The manufacturing process presented in this study opens a new way for making biomedical devices with low elastic constant, high strength to weight, and high resistance to wear. [ABSTRACT FROM AUTHOR]

[Display omitted] • Particle swarm algorithm is used to inversely optimize the alloy composition according to target performance. • An optimized feature set including 3 features is obtained by GA, interpretable ML and solid-solution strengthening. • A general design framework is summarized for prediction and composition optimization of various HEA performances. Two data-driven machine learning (ML) models were proposed for the hardness prediction of high-entropy alloys (HEA) and the composition optimization of high hardness HEAs, respectively. The hardness prediction model combined interpretable ML methods with solid solution strengthening theory, and the R 2 and RMSE values of 0.9716 and 39.2525 were respectively achieved under the leave-one-out validation method. The optimization model adopted an intelligent optimization algorithm to design the optimized elemental molar ratios of high hardness HEAs and was experimentally verified. A general design framework was summarized for prediction and composition optimization of various HEA performances. [ABSTRACT FROM AUTHOR]

[Display omitted] • CF/PEKK laminates were made via compression moulding and automated tape placement. • The effect of crystallinity of CF/PEKK properties was tested via nanoindentation. • CF/PEKK regions with a higher crystallinity possessed higher hardness and modulus. • A transition from fibre to bulk matrix properties was measured via nanoindentation. • Micromechanical studies exhibit the impact of manufacturing on performance. The present work seeks to characterise the micromechanical properties of carbon fibre/poly(etherketoneketone) (CF/PEKK) composites with different crystallinity levels and morphologies. CF/PEKK laminates were manufactured under various compression-moulding and automated tape placement (ATP) conditions. Nanoindentation experiments were performed at different locations across the thickness of the laminates to evaluate hardness and elastic modulus at the micron scale. The polymer matrix of compression-moulded laminates, which was found to be fully crystallised, performed significantly better than the matrix of the ATP laminates. The central region of the ATP laminates performed slightly better than regions close to the top and bottom surfaces, likely due to a higher crystallisation development in the central area. A transition in response from the fibre to the matrix bulk was observed across all samples via nanoindentation testing. Overall, the study of micromechanical properties can provide insight into the impact of manufacturing conditions on the composite's performance at the macro scale, ultimately contributing towards higher-quality end products. To the authors' best knowledge, the in-depth work presented in this article is the first to use nanoindentation to characterise the effect of manufacturing processes on the micromechanical properties of CF/PEKK laminates. [ABSTRACT FROM AUTHOR]

[Display omitted] • A novel Pt-15Ir-3Hf-0.5Y alloy with good high-temperature strength and ductility is prepared. • No Pt-Hf precipitates but three types of nanoclusters, clusters containing stacking fault, clusters at 1/2 〈0 1 1〉 dislocation core and clusters with short-range order are observed in the alloy matrix. • The alloy has a strong ageing strengthening effect through more and larger clusters formation. A novel ultra-high temperature Pt-15Ir-3Hf-0.5Y (wt.%) alloy was developed for the first time by high vacuum arc-melting, hot rolling and ageing treatment. The microstructures of the as-cast and hot-rolled and then post-aged samples were investigated. The alloy consists of the (Pt,Ir) 5 Y phase and matrix. Through transmission electron microscopy atomic resolution imaging, three types of nanoclusters, clusters containing stacking fault, clusters at 1/2 〈0 1 1〉 dislocation core and clusters with short-range order were observed in the matrix. The hardness at the ambient temperature of the alloy after hot rolling and ageing treatment was up to 443 HV and the tensile strength at 1500 °C was up to 47.8 MPa. Compared with the solid solution strengthened Pt-Ir binary alloys, the addition of Hf and Y can effectively improve the mechanical properties, which were achieved by introducing the combined effects of nanocluster strengthening and grain boundary strengthening of (Pt,Ir) 5 Y phase. Our findings provided new insights into designing the Pt-based superalloy with high strength and ductility. [ABSTRACT FROM AUTHOR]

[Display omitted] • The exceptional hardness of Ti-based materials, 40% plus above the hardness of the base alloy, was achieved without compromise to low specific weight of the material. • The addition of TiC to the alloy Ti-6Al-4 V in an amount of 40% leads to the formation of a discontinuous composite and an increase in the hardness of the material; with a higher particle content, the composite becomes continuous, exhibiting very fragile behavior. • TiC chemically reacts with the matrix alloy and forms a strong interfacial bond with the base alloy. • As a result of high temperature aging of the composite, the hard phases of Ti 2 C and Ti 3 AlC formed in the expense of a relatively soft matrix alloy and further contribute to a significant increase in hardness. Titanium alloy composites, reinforced with a light second phase and made using inexpensive powder metallurgy, attract considerable attention due to the directness of their intentional hardness increase without compromising low weight of materials. In this study the metal-matrix composites (MMC) of Ti-6Al-4V alloy reinforced with light and hard particles of TiC (up to 80%, vol.) were made using blended elemental powder metallurgy of hydrogenated titanium. Post-sintering solution treatment for 45 min. at 880 °C and 1000 °C and water quenching followed by the 5 hrs. aging at 550 °C was used to additionally refine the microstructure and properties of MMC. For the duration of thermal exposure throughout solution treatment and additional aging the matrix and reinforcement phase underwent distinct structural changes that modified the mechanical properties of materials. It has been shown that the used reinforcement presents an exceptional opportunity for hardening of Ti-based composites without compromising their low specific weigh. It can increase the hardness of material by more than 40% due to the ability of TiC to chemically react with the matrix to form a strong interfacial bond and its ability to form hard compounds of Ti 2 C and Ti 3 AlC in the expense of the relatively soft matrix alloy. [ABSTRACT FROM AUTHOR]

[Display omitted] • The effect of diffusive vs. deeply trapped hydrogen is deduced by time-dependent evolution of mechanical properties for ferritic alloys using novel in-situ nanoindentation during backside continuous hydrogen supply. • A linear relationship between hardness increase and hydrogen ingress is observed in the initial stage, with a more pronounced hardening effect for higher content of the studied substitutional elements. • An increase in dislocation density due to hydrogen is quantified by transmission electron microscopy. • Our data support the interpretation that hydrogen facilitates dislocation nucleation in the initial stage following the defactant theory; and we link the hardness increase to the dislocation density and friction stresses arising from diffusible hydrogen. Hydrogen embrittlement is common in metallic materials and a critical issue in industries involving hydrogen-related processes. Here we investigate the mechanical response upon hydrogen loading of ferritic Fe-16Cr, Fe-21Cr and Fe-4Al alloys. We use a novel in situ setup for electrochemical backside hydrogen charging during nanoindentation. Single-phase ferritic Fe-Cr binary alloys with high hydrogen diffusivity and low solubility, are ideal for in situ studies during hydrogen charging, particularly the effect of diffusible and lightly trapped hydrogen is targeted. The hardness increases linearly with increasing hydrogen content until a quasi-equilibrium state between hydrogen absorption and desorption is reached while Young's modulus remains unaffected. Above this transient region, the slope of the absolute hardness experiences a drastic decrease. The hardness variation in Fe-21Cr is anisotropic as determined for (1 0 0), (1 1 0) and (1 1 1) oriented grains. Increasing the Cr content enhances the hardening effect in (1 0 0) orientation: a 16.7 % hardness increase is observed in Fe-21Cr, while Fe-16Cr, shows an increment of 10.8 %. A Fe-4Al alloy increases slightly in hardness by only 4.3 % at the applied current density of 3 mA/cm2. The hardening effect is caused by enhancing dislocation density, as revealed by studying the cross-section underneath the nanoindentation imprints. [ABSTRACT FROM AUTHOR]

[Display omitted] • A bilayer hierarchical HEA thin film was obtained by magnetron sputtering. • The HEA film shows high hardness, good modulus and excellent corrosion resistance. • The outer nano-lamellar layer shows high nano-hardness but low surface potential. • The multi-functional films were obtained by adjusting the structure hierarchy. A two-step temperature-controlled magnetron sputtering procedure was adopted to obtain a bilayer hierarchical Fe 25.2 Co 25.2 Ni 27.4 Cr 22.2 high entropy alloy (HEA) thin film consisting of the external nano-lamellar layer and internal equiaxed zone, which displayed combined advantages of high hardness, good modulus and excellent corrosion resistance. The roles of heterogeneous nanostructure on the mechanical and corrosion behavior were revealed by nano-indentation and Scanning Kelvin probe (SKP) methods. Compared to the substrate 304 ASS, the hierarchical HEA film not only shows much higher nano-hardness and modulus values, but also possesses a higher electron transfer resistance (12158 vs 4567 Ω.cm2) and lower overall corrosion rate (6.28*10−4 vs 6.84*10−3 mm·year−1). Moreover, the outer nano-lamellar layer shows higher nano-hardness (∼8.1 GPa) but lower surface potential values (∼-261 mV) than those of the inter equiaxed zone (∼5.9 GPa and ∼−150 mV). The former arises from the significant grain refinement strengthening effect, while the latter is attributed to an obvious increase in the high energy and chemically active areas such as grain boundaries and triple junctions. This work demonstrates the capability of hierarchy to adjust the comprehensive performance of multi-functional films, which possess superior mechanical property and comparable corrosion performance than those of the as-cast bulk HEA alloys. [ABSTRACT FROM AUTHOR]

Abstract Owing to the unique layer-wise production method, additive manufacturing technologies have been widely adopted in rapid prototyping and tooling areas, which often require superior mechanical properties such as tensile strength and hardness. In current literature, most mechanical property studies focusing on additive manufactured materials mainly adopt experimental or simulation-based approaches, and therefore cannot be directly used to accurately estimate and predict the achieved mechanical properties. In addition, information regarding the mechanical properties of photosensitive liquid resin used in the Stereolithography additive manufacturing process is limited. Hence, in this paper, mathematical models are established to quantify the tensile strength and hardness of Stereolithography fabricated materials by estimating the solidification levels of both green parts and Ultraviolet post-cured parts. The established degree of cure model is shown to have an average prediction accuracy of around 94%. In addition, the mechanical property models have an average accuracy of 88% and 90% for tensile strength prediction, and 98% and 95% for hardness prediction of green parts and post-cured parts, respectively. It is also observed that the Ultraviolet post-curing process has the capability of significantly enhancing the studied mechanical properties. Graphical abstract Unlabelled Image Highlights • The tensile strength and hardness of photosensitive liquid resin are modeled based on the degree of cure. • The established degree of cure model has an average of 94% prediction accuracy. • The investigated resin consists of Hexane-1, 6-diol diacrylate, Isobornyl acrylate, Acrylate monomer, etc. [ABSTRACT FROM AUTHOR]

Abstract For the sake of enhancing hardness and wear resistance of Ti based materials, 50 vol% (TiB + TiC)/Ti64 composite coatings with different TiB/TiC ratios were fabricated by gas tungsten arc cladding (GTAC) on the network structured 3.5 vol% TiBw (TiB whisker)/Ti64 substrate. The results showed that primary TiB and TiC exhibited much larger sizes than their eutectic counterparts, and the two-scale reinforcements formed by the dissolution-precipitation mechanism predominated the hybrid coatings. In particular, most TiC was embedded within the TiB prism displaying an intergrowth structure with "dissimilar-joining" characteristic, which contributed to the hardness and wear resistance improvement. The remarkable hardness improvement was attributed to the following three-fold mechanisms: (a) load transfer strengthening from the primary TiB and TiC; (b) Orowan strengthening from the eutectics; and (c) Hall-Petch strengthening from the refined Ti64 matrix. Moreover, the plastic deformation resistance was significantly improved by the hybrid reinforcements, leading to the enhanced the anti-abrasion performance. Consequently, the coating exhibited a comparatively low wear rate (7.35 × 10−5 mm3·N−1·m−1) compared with the substrate (54.89 × 10−5 mm3·N−1·m−1), and the corresponded wear mechanisms are summarized as: brittle debonding, oxidation and slight micro-ploughing. Graphical abstract Unlabelled Image Highlights • (TiB + TiC) hybridly reinforced Ti64 coating was fabricated by low-cost arc cladding. • Wear resistance is about 7 times higher than substrate with brittle debonding wear mechanism. • Revealing evolution characteristics of hybrid reinforcements and intergrowth structures. • Property enhancing mechanism is revealed by mechanical tests under various load magnitudes. [ABSTRACT FROM AUTHOR]

Abstract The potential change in EU regulations may affect the traditional W-C-Co based cemented carbides industry and a methodology is required to accelerate the materials development with alternative binders. This work presents the ICME (Integrated Computational Materials Engineering) framework and the improved models that will enable tailor-made materials design of cemented carbides. The cemented carbide hardness is one of the key properties of the composites and here its close relation to the binder composition is in focus. Modeling the influence of alternative binder materials on the hardness of cemented carbides offers a way to optimize the composite properties of prospective binder candidates virtually, thereby reducing the development time and costs drastically compared to a classical trial-and-error method. The outline of a genetic algorithm is presented and the integration of the required models and tools, that are, or will become, available within this ICME framework, are presented. Graphical abstract Unlabelled Image Highlights • The developed computational framework allows for hardness design of conventional and alternative binder cemented carbides. • Investigating Ni-Fe based binder systems shows the importance of alloying elements for tailoring the binder hardness. • The integration in an optimization scheme based on a genetic algorithm enables automatic design of composite properties. [ABSTRACT FROM AUTHOR]

Abstract New powder-processed hardfacing Fe-based alloys are being developed to provide high wear and corrosion resistance in demanding pressurised water reactor environments. The triplex stainless steel alloy RR2450, developed from the parent austenitic alloy Tristelle 5183, has been created for this purpose. A detailed study into the stoichiometric sensitivity and phase balance within these alloys has been carried out, in order to better predict the microstructural evolution within this chemically complex class of alloys. After undergoing a hot isostatic pressing cycle, the RR2450 alloy is shown to evolve a triplex matrix of austenite, ferrite and a novel π-ferrosilicide phase, alongside numerous niobium, titanium and chromium precipitates. Investigation into large austenite and π-ferrosilicide phase variations between different batches of the RR2450 and Tristelle 5183 alloys has indicated that small stoichiometric adjustments allow these hardfacing alloys to be tailored to produce different microstructures for specific applications. Graphical abstract Unlabelled Image Highlights • Hardfacing steels with various triplex matrix phase fractions (austenite, ferrite and π-ferrosilicide) can be produced. • Alterations to the Si and Ni contents of these alloys are shown to be crucial to controlling the phase balance. • Greater fractions of the π-ferrosilicide matrix phase increase the alloy strength. • Adapting the phase balance allows hardfacing alloys, tailored to a particular application, to be created. [ABSTRACT FROM AUTHOR]

This investigation deals with the study of 1 wt% carbon nanotube (CNT) reinforced high velocity oxy-fuel sprayed conventional and nanostructured WC-Co coatings deposited on Ti-6Al-4V coupons. Coatings were also prepared from the as-received powders for comparison purpose. The reinforced coatings exhibited up to 30%, 10% and 33% increase in hardness, elastic modulus and cohesive strength, respectively. The graphene structure of the CNT was retained in the coating. The reinforced coatings demonstrated a significant reduction in specific wear rate during ball-on-disc tribometry. The forces and specific energy recorded during surface grinding of the reinforced coatings were substantially higher than those of the coatings produced from the as-received powders. The residual stress of the as-sprayed coatings was compressive in nature. The magnitude of this stress increased further on surface grinding. [ABSTRACT FROM AUTHOR]

Additively manufactured (AM) components usually have nonequilibrium microstructures. Post-built heat treatments are recommended for AM components to achieve homogenous microstructures. In this study, the effects were investigated of conventional solutionizing and precipitation hardening (H-900) heat treatments on the microstructure evolution of 17-4PH AM and wrought components. Microstructural characterization techniques including SEM, TEM and EBSD analysis were used on 17-4PH AM and wrought components to obtain quantitative information about the microstructure and phase evolution during these heat treatments. These microstructural studies demonstrate that 17-4PH AM components can achieve microstructures and hardnesses similar to those of wrought samples by post-built heat treatments. [ABSTRACT FROM AUTHOR]

The maximization of stable reverted austenite at room temperature through inter-critical tempering is a widely used method to reduce hardness in supermartensitic stainless steels. Nevertheless, partial martensitic transformation might occur due to insufficient compositional stabilization. In this work, we conducted a time-resolved triple-step inter-critical tempering, specially designed to obtain maximum austenite stability and minimum hardness through the progressive suppression of the martensitic transformation. The mechanism behind the progressive increase in stable reverted austenite was the generation of a meta-equilibrium state, which imposed a limit in both high temperature austenite reversion and room temperature austenite stabilization. Such limit corresponded to the high temperature volume fraction of austenite, obtained right before cooling from the first cycle. This effect was associated to the Ni-rich fresh martensite laths acting as local Ni compositional pockets, providing site-specific austenite reversion; and to the suppression of any additional nucleation at the Ni-poor matrix as the T0 temperature for austenite reversion was strongly increased. The softening mechanism was mainly controlled by the carbon arrest effect by the precipitation of Ti (C, N), which was completed after the first tempering cycle. Nevertheless, maximizing reverted austenite and suppressing fresh martensite at room temperature did not result in additional hardness reductions. [ABSTRACT FROM AUTHOR]

This study analyzes the influence of Cr content on hardness H, elastic modulus E and fracture toughness K IC of the M 2 B boride by means of nanoindentation experiments. Additionally, properties of the Fe 3 (C,B) phase are determined. Samples of the M 2 B phase are casted and microstructurally characterized by means of scanning electron microscopy, energy dispersive spectroscopy and X-ray diffraction. At a Cr content higher than 14.7 atom% the M 2 B phase transforms from tetragonal into orthorhombic structure. The tetragonal M 2 B type possesses an optimum of H (21 ± 1 GPa), E (373 ± 6) GPa and K IC (3.5 ± 0.7 MPa m ) at 4–5 atom% Cr. The hardness, modulus and toughness of the orthorhombic M 2 B phase increase with Cr content and reach values of H = 27 ± 0.7 GPa, E = 473 ± 9 of and K IC  = 3.26 ± 0.8 MPa m at maximal investigated Cr content of 55 atom%. The hardness of the M 2 B phases decreases around 2.3–3.2 GPa as a function of indentation depth, which is known as the indentation size effect. Hardness and fracture toughness of M 2 B phase outperform conventionally used M 7 C 3 carbides and are similar to MC-carbides. Findings can be used in novel alloying approaches in order to optimize the performance and reduce cost of tool steels. [ABSTRACT FROM AUTHOR]

Main regularities of the formation of microstructure and properties of multilayer nanostructured CrN/MoN films with periodically changing architecture of layers were considered. Coatings were fabricated by vacuum-arc evaporation of the cathodes (Arc-PVD) in nitrogen atmosphere (p N was 0.4, 0.09 and 0.03 Pa). CrN and γ-Mo 2 N nitride phases with fcc lattices and a small volume of metastable MoN x cubic phase were formed in the films at p N  = 0.4 Pa. The decrease of p N to 0.09 Pa causes the formation of β-Cr 2 N hexagonal phase. Preferential crystallographic orientation changes from [311] to [111] and [200] when bias voltage U b is −20, −150 and −300 V respectively. The nanocrystallites size in coatings with bilayer thickness λ = 44 nm decreases to 5.8 nm. The microdeformation grows from 0.4 to 2.3% when U b changes to −20 V. Coatings show high hardness of 38–42 GPa and H/E = 0.107. In a couple with results of tribological tests, coatings demonstrate strong wear resistance, which makes them appropriate and promising for industrial applications as protective ones. The effect of deposition conditions (p N , U b , λ) on composition, structure, hardness, toughness and wear resistance was studied to achieve superior mechanical and physical properties of coatings with long lifetime in harsh environment. [ABSTRACT FROM AUTHOR]

Using first principles calculations and experimental methods we show that B1 structured solid solution Ti x Nb y Al z N can be grown. The mixing free energy surface indicates that the alloys should decompose. Theoretical analysis of the thermodynamic driving force towards the spinodal decomposition shows that the force can be different in alloys with equally low thermodynamic stability but different Nb content, indicating that the detailed picture of the decomposition should also be different. Electron microscopy and nanoindentation underlines different age hardening of the samples. We demonstrate that an alloy with the optimized composition, Ti 0.42 Nb 0.17 Al 0.41 N combines high thermal stability and age hardening behavior. [ABSTRACT FROM AUTHOR]

Multicomponent carbide thin films of (CrNbTaTiW)C (30–40 at.% C) with different metal contents were deposited at different temperatures using non-reactive DC magnetron sputtering. The lattice distortion for the metal lattice was estimated to vary from about 3 to 5%. Most films crystallized in the cubic B1 structure but Ta/W-rich films deposited at 600 °C exhibited a tetragonal distortion. X-ray diffraction results show that near-equimolar films exhibited a strong (111) texture. In contrast, Ta/W-rich films exhibited a shift from (111) to (100) texture at 450 °C. The in-plane relationship was determined to MC(111)[-12-1]//Al 2 O 3 (001)[110] with a lattice mismatch of about 11% along the Al 2 O 3 [110] direction. A segregation of Cr to the grain boundaries was observed in all films. The microstructure was found to be the most important factor for high hardness. Less dense Nb-rich and near-equimolar films deposited at low temperatures exhibited the lowest hardness (12 GPa), while very dense Ta/W-rich high temperature films were found to be the hardest (36 GPa). No correlation was found between the lattice distortion and the hardness. Corrosion studies revealed that the multicomponent films exhibited excellent corrosion resistance, superior to that of a reference hyper-duplex stainless steel, in 1.0 M HCl. [ABSTRACT FROM AUTHOR]

In this study, gradient nanocrystallization and enhanced surface mechanical properties in commercial pure titanium, which were induced by an electropulsing-assisted ultrasonic surface rolling process (EP-USRP), were systematically investigated. The results indicated that EP-USRP at an optimum frequency of 500 Hz is advantageous over a conventional ultrasonic surface rolling process (USRP) in achieving excellent surface mechanical properties, including a lower friction coefficient and less wear loss (maximum depth of wear scar decreased to two-thirds of that of USRP). Such enhancements may be attributed to a higher surface maximum hardness (308 HV, increased by 46.7% compared to the turning sample), deeper severe plastic deformation layer (480 μm, ~0.5 times greater than that of USRP), smaller surface roughness (Ra 0.026 μm), and higher compressive residual stresses. There is a balance between electropulsing-induced ductility and ultrasonic impact-induced work hardening. At the optimum conditions, the mobility of immobile dislocations is remarkably improved owing to the thermal and athermal effects of electropulsing as well as the ultrasonic vibration energy from USRP, leading to higher strains and dislocation densities; these induce further dynamic recrystallization in the sub-grains until a new balance is reached. [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]

Thermodynamically stable C 3 N phases in the pressure range of 0–100 GPa are searched and calculated by ab initio evolutionary algorithm and density functional theory. Ground-state C 3 N phase at ambient pressure is predicted to be a layered structure with Cmmm space group. The previously reported Fd 3 ¯ m phase exists only in the narrow pressure range of 6.1–7.4 GPa, which transforms into a P 3 ¯ m 1 phase at 7.4 GPa and then into a R 3 ¯ m phase at 40.7 GPa. The increasing pressure drives the R 3 ¯ m phase to a C 2/ c phase at 76.9 GPa. Dynamical and mechanical stabilities of C 3 N phases are checked and confirmed by phonon dispersion and elastic constant calculations. It is diverse of the electronic properties of C 3 N with Cmmm (zero band gap), P 3 ¯ m 1 (wide gap of 4.55 eV), R 3 ¯ m (wide gap of 4.54 eV) and C 2/ c (narrow gap of 1.94 eV). The three-dimensional strong covalent C 2/ c C 3 N is superhard with high hardness of 79.5 and 86.9 GPa calculated by Chen and Gao models. Pressure-temperature phase diagram of C 3 N is firstly established and shows high temperature can significantly decrease synthesis pressures of C 2/ c phase, which gives a theoretical guidance for further experimental synthesis. [ABSTRACT FROM AUTHOR]

(NbTi)C nanoparticles were prepared using mechanical alloying (MA) and heat treatment process, and the nanoparticles pre-dispersed with Fe powder were introduced to 1045 steel. The microstructure of powders during different ball milling steps and as-casted steels were investigated using optical microscope (OM), scanning electron microscope (SEM), X-ray diffractometer (XRD) and transmission electron microscope (TEM). The results showed that the added carbides in as-cast steels were mainly composed of three kinds of types: uniform distribution; grain boundary center distribution and chainlike distribution. The uniformly distributed (NbTi)C nanoparticles in the matrix acted as effective heterogeneous nuclei that strongly refined the crystallization microstructure; the grain boundary center distributed particles interacted with the solid-liquid interface, thereby, hindered and restrained the movement of the solid-liquid interface; and the chainlike distributed nanoparticles move with the migration of solid-liquid interface and did not inhibit the interdendritic growth significantly. Compared with the cast steel without (NbTi)C nanoparticles, the modified steels have significantly refined microstructure, improved strength and increased hardness. With the further increase the amount of (NbTi)C nanoparticles, the efficacy of the (NbTi)C nanoparticles for refining crystallization microstructure weakened. [ABSTRACT FROM AUTHOR]

In this study, a novel friction-based welding technology was proposed for fabricating Al/Cu bimetallic tubes. The frictional heat and radial pressure during the friction-based welding process are used to achieve the metallurgical bonding between Al and Cu tubes in a rapid and efficient way. Successful joints indicate that this technology has the potential for fabricating bimetallic tubes. Microstructure evolution, bonding mechanism and mechanical properties of Al/Cu bimetallic tubes were also analyzed. Results reveal that columnar α-Al, intermediate transition layer and intermetallic compounds (IMC) are identified at the rotational speed of 950 rpm. While the rotational speed is decreased to 95 rpm, only solid-state diffusion occurs at the interface which results in three IMC layers, Al 2 Cu, AlCu, and Al 2 Cu 3 . The thickness of the Al 2 Cu is more significantly affected by the rotational speed than that of AlCu and Al 2 Cu 3 . Maximum hardness is observed at the reaction layer due to the formation of IMC. The appearance of intermediate transition and thick Al 2 Cu layer weakens the bonding strength of bimetallic tubes. The joints are fractured at the reaction layers, and the fracture exhibits typical brittle characteristic. Three crack propagation paths are observed at the interface of Al/Cu bimetallic tubes. [ABSTRACT FROM AUTHOR]

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]

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]

[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]

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]

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]