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Interrupted aging and creep tests were performed in the condition of 650 °C/70 MPa for P91 steel. The mechanisms of hardness and microstructure evolution during aging and creep were studied through hardness test, SEM/EBSD and TEM/EDS. By comparing the difference between aging and creep, the coupling effect of temperature and stress in P91 steel was elucidated. Results show that creep stress could accelerate the entire degradation process in P91 steel. Firstly, the dislocation density increased rapidly at the beginning of creep, and then decreased also at a high rate after reaching its peak value. On the other hand, the dislocation density decreased slowly in aging condition. Additionally, with the migration of grain boundaries under creep stress, some intergranular M23C6 entered inside grains and afterwards dissolved into matrix. On the other hand, other M23C6 which remained intergranular continuously ripened and congregated with time, and finally turned into large ones at triple junctions of grain boundaries. Furthermore, stress had the greatest impact on dislocation density, whereas temperature affected volume fraction of M23C6 the most. In creep condition, the degradation of mechanical properties of P91 steel was mainly caused by the reduction of dislocation strengthening which was followed by grain boundary strengthening.

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 Ti2C and Ti3AlC in the expense of the relatively soft matrix alloy.

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 (100), (110) and (111) oriented grains. Increasing the Cr content enhances the hardening effect in (100) 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.

A two-step temperature-controlled magnetron sputtering procedure was adopted to obtain a bilayer hierarchical Fe25.2Co25.2Ni27.4Cr22.2 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.

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.

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.

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.

[Display omitted] • More serious degardation happened on P91 steel during 650 °C/70 MPa creep than the one during aging. • Evolution of dislocation during creep was quite different from the one during aging. • The mechanism of M 23 C 6 evolution under stress and high temperature (creep) was elucidated. Mechanism of M 23 C 6 evolution during creep was elucidated. • Contribution of each strengthening mechanism was calculated and analyzed in both creep and aging conditions. Interrupted aging and creep tests were performed in the condition of 650 °C/70 MPa for P91 steel. The mechanisms of hardness and microstructure evolution during aging and creep were studied through hardness test, SEM/EBSD and TEM/EDS. By comparing the difference between aging and creep, the coupling effect of temperature and stress in P91 steel was elucidated. Results show that creep stress could accelerate the entire degradation process in P91 steel. Firstly, the dislocation density increased rapidly at the beginning of creep, and then decreased also at a high rate after reaching its peak value. On the other hand, the dislocation density decreased slowly in aging condition. Additionally, with the migration of grain boundaries under creep stress, some intergranular M 23 C 6 entered inside grains and afterwards dissolved into matrix. On the other hand, other M 23 C 6 which remained intergranular continuously ripened and congregated with time, and finally turned into large ones at triple junctions of grain boundaries. Furthermore, stress had the greatest impact on dislocation density, whereas temperature affected volume fraction of M 23 C 6 the most. In creep condition, the degradation of mechanical properties of P91 steel was mainly caused by the reduction of dislocation strengthening which was followed by grain boundary strengthening. [ABSTRACT FROM AUTHOR]

[Display omitted] • A method utilizing sol–gel assisted carbothermal reduction was developed to facilitate the synthesis of multi-branched HfB 2 with high crystallinity and aspect ratio. • By modulating the atomic molar ratio of Hf: B: C in the reactants, the aspect ratio of HfB 2 microrods can be tailored from 9.52 to 12.68. • Oriented attachment and reactive templated growth of the growth mechanisms of HfB 2 microrods would guiding significance for one-dimensional growth of ceramic powders. • The fracture toughness of the sample was significantly enhanced upon the addition of 6 wt% HfB 2 microrods, increasing from 3.98 MPa m1/2 to 7.24 MPa m1/2. Development of strategies to toughen HfB 2 ceramic, improve their mechanical properties is the key to promote their applications in extreme thermal environments. This study explores a kind of self-toughening method of HfB 2 ceramic by incorporation the highly crystalized multi-branched HfB 2 microrods. The multi-branched HfB 2 microrods were synthesized by sol–gel process and carbothermal reduction, exhibiting length of 6–13 μm and diameter of 0.60–1.50 μm, respectively. Detailed analysis of the formation mechanism of HfB 2 microrods reveals that the HfB 2 multi-branched structure is a collaborative consequence of orientation attachment mechanism and reactive templates growth, in which process monoclinic HfO 2 crystals transform into crystalized HfO 2 microrods at ∼1000 °C, and worked as template to induce one-dimensional HfB 2 microrods. Furthermore, spark plasma sintering experiments show that the optimal mechanical properties were attained by 6 wt% addition of HfB 2 microrods, comparing with HfB 2 ceramics free of self-toughening agent, the hardness and fracture toughness of self-toughened HfB 2 ceramic improved by 8.82 % and 81.91 % respectively, demonstrating the effectiveness of self-toughening of the microrods without sacrificing the hardness of HfB 2 ceramic. Thus, it can be seen that the work has important reference value for the synthesis of HfB 2 powder with different morphologies and the toughening of HfB 2 ceramics. [ABSTRACT FROM AUTHOR]

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.

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.

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.

Deviation from equimolar composition in high-entropy multielement ceramics offers a possibility of fine-tuning the materials’ properties for targeted application. Here, we present a systematic experimental and theoretical study on the effects of alloying equimolar pentanary (TiHfNbVZr)N and hexanary (TiHfNbVZrTa)N high-entropy nitrides with Al. Although being predicted to be metastable by ab initio density-functional theory calculations, single-phase fcc NaCl-structured solid solution thin films with Al solubility limits as high as x ∼ 0.51–0.61 in (TiHfNbVZr)1-xAlxN and x ∼ 0.45–0.64 in (TiHfNbVZrTa)1-xAlxN are synthesised utilizing a hybrid deposition technique that offers dynamic mixing of film atoms from Al+ subplantation and non-equilibrium growth conditions leading to quenching of the desired film structure. In experimental studies supplemented with density-functional theory calculations, it is demonstrated that Al concentration in alloys with the multielement compositions of high-entropy nitride thin films determine hardness, yield strength, toughness, and ability to deform plastically up to fracture due to different deformation mechanisms arising from the electronic structure and phase compositions.

Significant hardening effect due to Fe concentrations in Ni-based alloys with face-centered-cubic structure has been studied by using a combined experimental and atomistic-based computational approach via nanoindentation tests. The obtained experimental load–displacement data for the [001] crystal orientation reached a qualitative good agreement with molecular dynamics simulations results, leading to strong evidence that the main strengthening factors are associated to sluggish dislocation diffusion, reduced defect sizes and the nucleation of tetrahedral stacking faults. Here, interstitial type prismatic dislocation loops mainly formed by ⅙〈112〉 Shockley dislocations are nucleated during the loading process, where their interaction leads to the formation of pyramidal shaped stacking fault which are mainly created by ⅓〈100〉 Hirth dislocations lines. Observing both types of defects coexisting in the same plastic deformation zone by both approaches. Reported mechanical data, measured experimentally and interpreted numerically, are also in accordance with microstructural SEM and TEM investigations.

[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]

Accurately predicting properties of steels containing martensite by using models based on traditional strengthening mechanisms remains a challenge. In this study, a smart machine learning model possessing two-dimensional microstructure input terminals was developed using high-throughput experiments and machine learning on steels for low-temperature service. An algorithm based on a convolutional neural network enriched with the two-dimensional input terminals increased the prediction accuracy, achieving an average microhardness error of as low as 14.37 HV for the validation set. The improved prediction accuracy is ascribed to the comprehensive strengthening mechanism and coupling of strengthening effects contained in the multifarious input terminals. The information acquisition and cross-correlation of substructures related to strengthening mechanism played an important role. The reported strategy can deepen the cognition of the strengthening mechanism of tempered martensite. It is promising for application to different steels containing tempered martensite.

In this study, an attempt is made to control the WC-Co two-phase microstructures by laser powder-bed fusion (LPBF) process using cemented carbide powders with different compositions of WC-25Co (mass%) and WC-17Co (mass%) and post heat-treatment at 1380 °C. The as-built cemented carbide samples had different microstructures from those of the cemented carbides fabricated by conventional manufacturing methods. The microstructures of the as-fabricated WC-25Co and WC-17Co cemented carbides were characterized by two types of regions. Region 1 consisted of W2C and W3Co3C phases, including numerous pores and defects. Region 2 consisted of WC and Co phases. Post heat-treatment of the LPBF-built WC-25Co sample at 1380 °C led to the formation of a defect-free WC-Co two-phase microstructure. In contrast, the W3Co3C phase remained in the LPBF-built WC-17Co sample even after heat treatment. The addition of carbon to the WC-17Co powder prevented the formation of the W3Co3C phase in the cemented carbide processed by LPBF and subsequent heat treatments. The addition of carbon to the WC-17Co powder had a slight effect on the hardness of as-fabricated samples, but reduced the hardness of heat-treated samples. The reduced hardness was attributed to the increased volume fractions of the WC and W3Co3C phases.

Research that seeks to mimic the complex hierarchical structures of organisms is often conducted as a technique for breaking through the characteristic limits of materials. The coconut crab, Birgus latro, is a rare organism with the greatest force; it has a pinching force 90 times its body weight. The correlation between the tissue structure, hardness, and composition of the coconut crab claw was studied using a materials science approach. The exocuticle adjacent to the surface was approximately 0.25 mm thick, which accounts for about 10% of the exoskeleton’s thickness of 2.5 mm. It had a twisted plywood pattern structure rotated 180° around an axis normal to the surface; its stacking height was about 2.3 μm. No such plywood structure was observed in the endocuticle, which is 10 times thicker. The hardness of the exocuticle was about five times that of the endocuticle and this increase was due to the dense tissue structure and calcium carbonate calcification. In the intermediate layer, the hardness and composition also changed significantly. Three-dimensional analysis have been very helpful in understanding the complex tissue structure. The tissue structure of the coconut crab claw may provide ideas for developing stronger, tougher ultimate materials.

Face-centred cubic (fcc-) Mo–N and Ta–N exhibit an inherent driving force for vacancy formation. To study their interaction and effects on structural evolution and mechanical properties, we synthesised Mo–Ta–N coatings by reactive magnetron sputtering using nitrogen-to-total pressure ratios, pN2/pT, of 0.32 and 0.69.Low pN2/pT results in high concentration of N vacancies, which stabilise single-phase fcc-Mo1-xTaxNy up to x = 0.76. These solid solutions follow the MoN0.5–Ta0.875N0.875 quasi-binary tie line. Compressive residual stresses, σ, indentation hardness, H, and toughness, KC, increase with Ta content, reaching their maxima of (on average) -2.0 GPa, 28 GPa, and 7.0 MPa√m, respectively, within the x range 0.38–0.69. Higher Ta contents favour higher concentration of metal vacancies deteriorating the properties.High pN2/pT favours the formation of fcc-Mo1-xTaxNy rich in metal vacancies, which however always coexists with a hexagonal phase. Within the x range 0.33–0.66, the fraction of the hexagonal phase is negligible, and σ, H, and KC deviate from −1.0 GPa, 28 GPa, and 2.9 MPa√m, respectively, within the error of measurements.The combination of experimental and theoretical studies demonstrates the power of point defects in stabilising desired crystal structures and improving mechanical properties through the thereby tuned atomic configuration.

[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]

Application of an external magnetic field during heat treatment affects the hardness of magnetic Fe-Cr-Co alloys. The microstructure and composition at atomic scale, as well as the hardening mechanisms need extensive studies. Using atomic resolution STEM, we investigated the effect of a 3 T magnetic field on the spinodal decomposition, as well as microstructure and hardness in step-aged Fe27wt. %Cr15wt. %Co samples. Spinodal decomposition resulted in a homogeneous α phase transforming into an Fe-Co rich α1 phase and a Cr rich α2 phase. Although α1 and α2 showed distinct contrast at low magnification Z-contrast images, close examination at atomic scale of the samples showed no sharp α1/α2 interfaces. Inside each phase, composition fluctuations occurred. A 3 T external magnetic field during step aging increased the size of the α1 phase and introduced microstructural anisotropy, which is desired for permanent magnet applications, In addition, the spinodal decomposition increased the hardness. Annealing in a 3 T magnetic field decreased the hardness but increased the ductility, which is desirable for manufacturing permanent magnets. The change in hardness values is attributed to the composition fluctuations of Fe, Cr and Co, and we further discuss the mechanisms for composition fluctuations and hardness.

Copper alloys with high strength and electrical conductivity are ideal candidates for a wide range of civilian and engineering applications. Traditional methods of alloy design, such as “trial and error” experiments, are costly and time-consuming, limiting the discovery of Cu alloys. Machine learning (ML)-based technology facilitates a better understanding on inter-relationships within massive experimental datasets, and shortens the development cycle of new alloy systems. Herein, we propose a method of material design based on ML to discover high-performance Cu alloys. The ML models are trained from “discarded” experimental data that show undesirable hardness and/or electrical conductivity. We constructed effective Gaussian process regression-based models successfully from limited training data by engaging additional features. The predicted Cu alloys were experimentally synthesized and characterized, exhibiting superior hardness or electrical conductivity with respect to original training data. The increase of hardness is due to precipitation of second-phase Co-Ti and Fe-Ti compounds during aging, while the rise of electrical conductivity is caused by a purification effect of the precipitates on Cu matrix. The impact of physical features on ML models was further evaluated by a genetic algorithm. Our findings suggest that ML holds great potential for developing high-performance Cu alloys.

Wire + arc additive manufacturing (WAAM) with cold metal transfer (CMT) process can reduce cost and lead time during the production of large-scale Ni-based components used in the transportation and energy sector. This paper investigates the effects of processing parameters and heat treatments employed on CMT-WAAM of a precipitation hardenable Ni-based alloy – Inconel 718. The process stability was analysed by electrical transients and melt pool imaging, showing an opposite trend to the measured heat inputs. A 1.2 mm diameter wire permitted deposition widths of 5.92–13.15 mm, but widths larger than ~10 mm decreased the arc stability considerably. Laves length and carbide diameter decreased with travel speed, while the as-deposited hardness increased. These observations permitted a linear wall to be fabricated with a minimal heat input per layer of 181–185 J/mm. An increase in the solution treatment temperature from 980 to 1040 °C reduced microsegregation, Laves and δ phase precipitation. Localised regions with high microhardness were found near interlayer regions due to a local dissolution of Nb-rich eutectic phases. Compared to powder-based additive manufacturing, CMT-WAAM IN718 exhibits a larger melt pool size and lower as-deposited hardness, but has been found to show satisfactory ageing response and similar Laves phase area fraction.

Equiatomic CrMnFeCoNi high-entropy alloy (HEA) known as Cantor alloy was extensively studied because of intriguing mechanical properties and fracture toughness. However, the HEA exhibits relatively low yield strength due to its intrinsic face-centered cubic lattice structure. In the present letter, crystalline/amorphous dual-phase CrMnFeCoNi alloy was deposited via magnetron sputtering technique. NC HEA with grain size of only ~7.2 nm was derived from low temperature annealing. The hardness reaches to 13.76 GPa, which is the maximum ever reported for CrMnFeCoNi HEA, and the contributions of the NC HEA microstructural characteristics to the ultra-high hardness were revealed. It was proposed that the quasi-dislocation-free crystalline structures and fully relaxed grain boundaries result in the significantly enhanced hardening and thermostability derived in the annealed NC HEA.

Over the years, there have been many improvements to the depth sensing indentation testing methodology and measurement electronics. These advancements provide opportunities to develop novel testing capabilities and also improve the reliability of the measurements. In this regard, a comprehensive model for simulating a constant indentation strain rate continuous stiffness measurement (CSM) test that includes the elastic-plastic response of the material and the response of the phase lock amplifier (PLA) is developed to understand the parameters affecting the precision and accuracy of the measurements. A novel test methodology that does not require closed-loop feedback is developed based on the model predications, and is found to improve the precision and accuracy of the CSM based indentation measurements. A procedure to correct for the plasticity error during CSM testing is also developed. Guidelines for selecting test parameters to stay within an acceptable level of error are established.

A comprehensive model for simulating a constant indentation strain rate test with continuous stiffness measurement (CSM) has been developed in a previous work [20]. A procedure for correcting errors associated with plasticity during CSM based testing is also developed. Furthermore, a new method that uses a fixed ratio of the amplitude of the sinusoidally varying portion of the instantaneous load to the load's mean value (AC to DC) during CSM testing is proposed that can reduce the plasticity error and improve the signal-to-noise ratio (SNR) in stiffness. In this work, experimental results are presented to assess the accuracy of the simulation results in terms of the displacement waveforms in response to the imposed load oscillations, the functional dependence of the plasticity error and the SNR. A comparison of the experimental results between the new and the traditional CSM methods is also presented and the advantages of the new method are demonstrated. Furthermore, recommendations for performing indentation testing using CSM with improved precision and accuracy are provided.

In this work a new ultra-high temperature (UHT) nanoindentation system for testing at up to 1100 °C is presented. The system is capable to perform indents from small scale up to large indentation depths due to the combination of a 1 N actuator and a frame stiffness of >1·106Nm even at 1100 °C. Dynamic testing allows a continuous determination of the contact stiffness (CSM) and thus also the depth-dependent hardness and indentation modulus. Low drift rates can be achieved by an independent tip and sample heating. Operating the nanoindenter inside a scanning electron microscope (SEM) equipped with a high temperature backscattered electron (BSE) detector opens the possibility of in-situ observations, as high vacuum minimizes oxidation effects. The HT capability of the system is demonstrated on three reference materials: fused silica, molybdenum assessing the change in modulus with increasing temperature using constant strain rate tests (CSR). The creep response of single crystalline Ni has been assessed by strain rate jump (SRJ) as well as a step-load and hold creep (SLH) method. The resulting modulus, hardness as well as the strain rate sensitivity from RT up to 1100 °C are in good accordance with literature data, highlighting the applicability of the system.

[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]

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]

[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]

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]

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]