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With the increasing demand for highly integrated circuits to optimize energy efficiency, reduce weight, and improve mechanical properties, finding a Magnesium (Mg) matrix material with excellent mechanical strength and high thermal conductivity poses a significant challenge. In this work, titanium (Ti) particles were introduced into AZ91 (Mg-9Al-1Zn) alloy to fabricate Ti/AZ91 composites, employing a combination of stir casting, extrusion and rolling processes. This strategy simultaneously enhances the mechanical properties and thermal conductivity of the Ti/AZ91 composites compared with AZ91 alloy. The incorporation of Ti particles serves to refine grains, expediting the formation of Mg 17 Al 12 phase within the Mg matrix. Optimal comprehensive mechanical properties are attained in 10 wt% Ti/AZ91 composite, exhibiting an ultimate tensile strength of 365 MPa, an elongation of 11.9 %, and a significantly low wear rate of 4.548×10−3 mm3/m. Notably, the 10 wt% Ti/AZ91 composite shows a 41.1 % reduction in wear rate relative to the AZ91 alloy, attributed to the incorporation of hard Ti particles. Furthermore, the thermal conductivity of the 2.5 wt% Ti/AZ91 composite exhibits a significant enhancement over that of the AZ91 alloy. Detailed discussions are provided on the fundamental mechanisms responsible for strengthening, wear resistance, and thermally conductive in Ti/AZ91 composites. These results highlight the substantial potential of Ti/AZ91 composites for lightweight structural applications, such as highly integrated circuits requiring excellent mechanical properties and high thermal conductivity. [Display omitted] • The 10Ti/AZ91 composite demonstrates a remarkable improvement in UTS, EL and wear resistance. • Enhanced mechanical properties results from the deformable Ti particles, refined grains, and weakening of texture. • The Ti/AZ91 composites possess exceptional thermal conductivity while maintaining high strength. [ABSTRACT FROM AUTHOR]

In this work the effects of Al and Ti element addition on the microstructure and mechanical properties of CoCrNi medium-entropy alloys (MEAs) has been investigated. A novel (AlTi) 2x (CoCrNi) 100–2x MEAs was fabricated by using powder plasma arc additive manufacturing technique. The influences of Al and Ti elements on the microstructure, mechanical properties and strengthening mechanisms were analyzed by XRD, EBSD and TEM. The (AlTi) 2x (CoCrNi) 100–2x MEAs exhibited columnar crystal structure, but the average grain size and texture decreased continuously with increasing values of x. Moreover, tensile test results showed that (CoCrNi) 90 Al 5 Ti 5 alloy possessed strength-ductility balance (yield strength, ultimate tensile strength and elongation to failure of 664 MPa, 897 MPa and 19.3 %, respectively). The analysis on the strengthening mechanism showed that the solid solution strengthening effect was more dominant with increasing of the x in all alloys. (CoCrNi) 94 Al 3 Ti 3 and (CoCrNi) 90 Al 5 Ti 5 have similar average grain sizes, wherein the difference in mechanical properties between both the alloys can be mainly attributed to the formation of fine grain sizes. (CoCrNi) 90 Al 5 Ti 5 has a small amount of dislocations, solid solution strengthening and grain boundary strengthening are the main sources of the excellent properties. • A novel (AlTi) 2x (CrCoNi) 100–2x MEAs were firstly produced by powder plasma arc additive manufacturing. • The (CoCrNi) 90 Al 5 Ti 5 MEA reaches a balance between strength and ductility well comparing with the current HEAs/MEAs. • The main strengthening contributions are solid solution strengthening and grain boundary strengthening. [ABSTRACT FROM AUTHOR]

Mechanically alloyed AlCoCrCuFeNi high-entropy alloy (HEA) powders were used as binder to fabricate WC/HEA composites by spark plasma sintering. The effects of sintering temperature, duration time and binder content on microstructures and mechanical properties were studied. Compared with cobalt binder, the HEA binder has an advantage on the inhibition of WC grain growth due to the sluggish diffusion effect, and the average WC grain size decreases with increasing HEA binder content. Furthermore, the fracture toughness of WC/HEA composites firstly increases with increasing Vickers hardness and then decreases. A good comprehensive mechanical property was obtained after sintering at 1250 °C for 5 min with 10 wt.% HEA binder under a sintering pressure of 30 MPa. The Vickers hardness is 1922 HV 30 and the fracture toughness is 10.41 MPa m 1/2 , which are higher than those of commercial WC/Co composites. Therefore, the AlCoCrCuFeNi high-entropy alloy has a potential to be a binder for WC. [ABSTRACT FROM AUTHOR]

Ultrafine WC cemented carbides with 10 wt% mechanically alloyed Al x CoCrCuFeNi (x is the aluminium content in molar ratio and ranges from 0 to 1.5) high-entropy alloy (HEA) binders were fabricated by spark plasma sintering. The influences of the HEA binders on the microstructures and mechanical properties of WC-HEA cemented carbides were discussed. Due to the sluggish diffusion effect of the HEA binders, the WC grain growth activation energy of WC-HEA cemented carbides is significantly higher than that of WC-Co alloy. Consequently, the grain growth of WC is inhibited during sintering, and an ultrafine microstructure can be obtained. With increasing Al content of HEA binders, both the relative density of WC-HEA cemented carbides and the hardness of HEA binders increase, which contributes to the high hardness of WC-HEA cemented carbides. The fracture toughness of WC-HEA cemented carbides is codetermined by the wettability of HEAs on WC and the intrinsic sintering property and deformability of HEA binders. Therefore, the WC-HEA cemented carbide with 10 wt% Al 0.5 CoCrCuFeNi high-entropy alloy binder exhibits the best combination of Vickers hardness and fracture toughness, which are 2071 ± 6 HV 30 and 10.3 ± 0.1 MPa m1/2, respectively. • Ultrafine WC-HEA composites without grain growth inhibitor were fabricated by SPS. • The component of HEA binder strongly affected WC grain growth activation energy. • Effects of HEA binders on mechanical properties of WC-HEA composites were studied. [ABSTRACT FROM AUTHOR]

SiC fiber reinforced mullite matrix (SiC f /Mu) composites were prepared via an infiltration and sintering process using SiC and Ti 3 SiC 2 as inert fillers. The effects of SiC and Ti 3 SiC 2 fillers on microstructure, mechanical, dielectric and microwave absorption properties of the composites were studied. The composite with 15 wt% SiC filler obtained a flexural strength of 300 MPa. The complex permittivity of the composite was enhanced from 12.3−j22.1 to 14.2−j39.7 at 10 GHz when the Ti 3 SiC 2 content increased from 10 wt% to 30 wt%. By adding 15 wt% SiC and 10 wt% Ti 3 SiC 2 in the matrix, both mechanical and microwave absorption properties of the SiC f /Mu composites were significantly improved. A flexural strength of 292 MPa and a failure displacement of 0.47 mm were obtained for the composite with hybrid SiC/Ti 3 SiC 2 fillers. The composite with a thickness of 2.9 mm obtained an effective absorption bandwidth of 3.3 GHz (from 9 to 12.3 GHz), with a minimum reflection loss of −53 dB at 8.64 GHz. Results indicated that the SiC f /Mu composite with hybrid SiC/Ti 3 SiC 2 fillers was one of the excellent structural-functional candidates for military application. • The composite with hybrid SiC/Ti 3 SiC 2 fillers possesses excellent properties. • The flexural strength and failure displacement are 292 MPa and 0.47 mm. • An effective absorption bandwidth of 3.3 GHz (from 9 to 12.3 GHz) is obtained. • A minimum reflection loss of −53 dB at 8.64 GHz is obtained. [ABSTRACT FROM AUTHOR]

Hypereutectic Al-Fe alloys are extremely brittle owing to the formation of coarse Fe-rich intermetallics in the Al matrix. In this study, a Ce-rich rare-earth (RE) mixture was introduced to modify an Al-5Fe binary alloy, and the crystallization, microstructure, and mechanical properties of the alloy were investigated. The experimental results indicated that the RE addition decreased the temperature of the primary Al 3 Fe phase, enhanced the temperature of the eutectic transformation, and disturbed the normal crystallization process of eutectic α-Al crystals by decreasing the intrinsic growth along the preferential close-packed (111) Al plane and promoting the growths depending on the sub-closed (200) Al plane. Furthermore, RE addition refined the primary Al 3 Fe phases and formed Al-Ce eutectics in the as-cast state of the alloy. Fine nodules and rods of the Al 4 Ce and AlCe phases containing La elements were produced through homogeneous annealing via the decomposition of the Al-Ce eutectics and precipitation of REs from the RE-enriched area. Rolling further broke up the coarser primary Al 3 Fe phases into short rods and particles and caused the Al-Ce and Al-Fe phases to become uniformly distributed in the Al matrix. A mixed cleavage and dimple fracture was produced by RE modification, annealing, and rolling. The optimized amount of added RE mixture for improving the microstructure and mechanical properties of the alloy was 0.9 wt%. • RE addition decreased the primary temperature of Al 3 Fe phase. • RE addition inhibited intrinsic growth of eutectic α-Al along (111) plane. • RE addition promoted the growth of eutectic α-Al along sub-closed (200) plane. • RE addition refined primary Al 3 Fe phases and formed Al-Ce eutectics. • 0.9 wt% RE was optimized for improving microstructure and mechanical properties. [ABSTRACT FROM AUTHOR]

Abstract P 2 O 5 -added Li 2 O-SiO 2 -Si 3 N 4 glasses were prepared by melt-quenching the liquid inside a glove box under a N 2 atmosphere. Studies on crystallization kinetics of the glasses show that the crystallization of oxynitride glasses is controlled by the three-dimensional interfacial growth mode of crystals (Avrami index = 2.70–3.90). The introduction of the nucleating agent P 2 O 5 can increase the crystallization ability, and the crystallization activation energy is reduced. X-ray diffraction and scanning electron microscope were used to investigate the crystallization behavior and phase formation of the glass-ceramics. In general, the addition of 3.0 mol% nucleating agent P 2 O 5 and two-step heat-treatment facilitate the precipitation of rod-like Li 2 Si 2 O 5 crystals with high aspect-ratio, which are uniformly embedded in the glass matrix and show interlocking and uniform morphology, thereby improving the mechanical properties of Li 2 O-SiO 2 -Si 3 N 4 oxynitride glass-ceramics. This work provides a roadmap for the preparation of high performance glass-ceramics. Highlights • Crystallization kinetics study show three-dimensional interfacial growth mode for glasses. • P 2 O 5 can act as effective nucleating agent to promote crystallization of oxynitride glass. • Rod-like Li 2 Si 2 O 5 with high-aspect-ratio contribute to improvement of bending strength. • This work provides a roadmap for the preparation of high properties glass-ceramics. [ABSTRACT FROM AUTHOR]

Abstract Novel porous CaO-Al 2 O 3 -SiO 2 -Si 3 N 4 glass-ceramics with in-situ grown rod-like β-Si 3 N 4 crystals were fabricated by sintering under a nitrogen atmosphere. Sintering behavior, microstructures and mechanical properties of various compositions in the CaO-Al 2 O 3 -SiO 2 -Si 3 N 4 system were investigated, using differential scanning calorimeter (DSC), X-ray diffractometry (XRD) and scanning electron microscopy (SEM) methods, followed by physical and chemical property measurements. Depending on our experiments, the coexistence of CaO-Al 2 O 3 -SiO 2 glass and α-Si 3 N 4 can lower the phase transition temperature of α-Si 3 N 4 and promote the in-situ formation and growth of β-Si 3 N 4 grains during sintering process. The in-situ grown rod-like β-Si 3 N 4 grains in the glass-ceramics are useful to the improvement of physical and chemical properties by addition of α-Si 3 N 4 to the system. This was attributed to that the in-situ grown β-Si 3 N 4 grains formed a spatial inter-locking microstructure. The physical and chemical properties of the porous glass-ceramics are mainly determined by the β-Si 3 N 4 content, the porosity and the residual glassy phase. The porous CaO-Al 2 O 3 -SiO 2 -Si 3 N 4 glass-ceramics with high porosity, high mechanical strength and low dielectric constant were obtained, indicating it is potential high-temperature industrial applications. Highlights • Porous CaO-Al 2 O 3 -SiO 2 -Si 3 N 4 glass-ceramics with excellent properties were obtained. • CaO-Al 2 O 3 -SiO 2 glass could effectively promote α-to β-Si 3 N 4 phase transformation. • Porosity and β-Si 3 N 4 content are the key factors that affect the properties. • Porous glass-ceramics show promise for high-temperature industrial applications. [ABSTRACT FROM AUTHOR]

Abstract An equiatomic AlCrCuFeNi high entropy alloy (HEA) is fabricated successfully from the alloy powders using selective laser melting (SLM). Microstructural characteristics and mechanical behavior of SLMed AlCrCuFeNi samples under optimal SLM processing parameters are studied in detail. It is revealed that the SLMed AlCrCuFeNi HEA shows high crack sensitivity, and the optimum processing window is narrow. The formation of FCC phase is inhibited, resulting in a simple BCC solid solution to accommodate high lattice distortion and elastic strain induced by rapid cooling rate for the SLMed AlCrCuFeNi HEA. Moreover, unique fine columnar grains containing multiple ultrafine sub-grains structures appear within the molten pool and present a <100> preferred orientation. Nano-scale Cu-rich phases precipitate and exhibit chain-like at HAGBs while granular shape at LAGBs. Also, anomalous alternating bright and dark structures containing B2 and A2 phases with the width about 22 nm appear at the sub-grain boundaries due to rapid solidification. The SLMed AlCrCuFeNi HEA possesses superior properties with a compression strength of 2052.8 MPa and a fracture strain of 6.8% compared to the corresponding casting material. Fracture analysis indicates that the SLM (0°) specimen exhibits quasi-cleavage fracture while the SLM (90°) specimen shows intergranular fracture. The grain boundary strengthening effect, <100> preferential growth orientation of BCC grain and the existing microcracks are proposed to explain the anisotropy of compression properties. Highlights • A dual-phase high entropy alloy is fabricated using selective laser melting. • Unique columnar grains containing multiple ultrafine sub-grains are discovered. • Nano-scale Cu-rich phases exhibit chain-like at HAGBs while granular at LAGBs. • Anomalous spinodal structures containing B2 and A2 phases are discovered. • Anisotropy of compression properties exists in the SLMed AlCrCuFeNi alloy. [ABSTRACT FROM AUTHOR]

Abstract The magnesium matrix nanocomposites (10 vol% and 15 vol% of SiC particles) with a hierarchical structure, which contained flake-like soft phases, were investigated by compression and modeling. Fortunately, the unique malleability of hierarchical Mg nanocomposites was observed. The fracture surfaces indicated that the hierarchical Mg nanocomposites demonstrated ductile rupture. The "pull-out" phenomenon on the fracture surfaces suggested that the flake-like soft phase could sustain the additional deformation, consequently improving the malleability of Mg nanocomposites. Additionally, the modeling demonstrated that the effects from soft phase were not negligible, where the modified model exhibited a better agreement on the yield strength of the hierarchical Mg nanocomposites. Highlights • The unique malleability of hierarchical Mg nanocomposites was recorded with ductile rupture. • The "pull-out" of the flake-like soft phase in the hierarchical nanocomposite was observed. • A modified strengthening model was proposed to predict the yield strength. [ABSTRACT FROM AUTHOR]

Mullite-based ceramic tiles were successfully prepared using only high-alumina fly ash (HAFA) at relatively low sintering temperatures (1100–1400 °C). The effects of alkali activation on the chemical composition, mineral phase, and morphology of the HAFA were respectively characterised by ICP-OES, XRD, and SEM methods. The alkali-activation pretreatment not only modifies the chemical composition of HAFA to match that of mullite, but also can introduce Na-rich compounds to promote sintering. The macroscopic and microscopic characteristics of the fully ash-based ceramic tiles formed at different sintering temperatures were examined. The ceramic samples sintered at 1300 °C exhibited optimal post-sintering properties (relative density: 90.85%, water absorption: 0.10%, rupture modulus: 109.67 MPa, linear shrinkage: 15.70%, and apparent porosity: 0.68%) and a well-developed cubic puncheon-shaped mullite morphology. Finally, through the isothermal sintering method, the melt viscosities and the sintering kinetics were calculated theoretically, and the results show that the alkali activation could dramatically reduce the melt viscosity and the apparent activation energy. This research may provide a new method in utilising the vast amounts of HAFA waste to produce mullite-based ceramic tiles at low costs. [ABSTRACT FROM AUTHOR]

Reduced graphene oxide modified by silver nanoparticles (Ag-RGO) has been employed as a reinforcing component to prepare the copper matrix composites. The Cu composites with 0.6 vol% Ag-RGO exhibit a significant improvement in the yield strength and ultimate tensile strength, being approximately 98% and 93% higher than that of pure Cu, respectively, much better than the RGO/Cu composites. Simultaneously, the electrical conductivity of Ag-RGO/Cu composites could reach 92.69% IACS. The significant strength enhancement is attributed to the addition of Ag nanoparticles which prevent the agglomeration of the RGO and enhance adhesion between the RGO and the Cu matrix. The results indicated that Ag-RGO is an effective reinforcing component to improve the mechanical properties of the graphene/metal composites. [ABSTRACT FROM AUTHOR]

Using a new design strategy for the metastable phase in transformation induced plasticity (TRIP) steels, we have successfully manufactured a 7 wt.% Mn containing steel with an excellent combination of mechanical properties (950 MPa ultimate tensile strength and 63% total elongation) via warm rolling and intercritical annealing (IA) processes. Compared with the cold rolled microstructure that is usually completely recrystallized during annealing, the warm rolled microstructure is just partially recrystallized due to the lower driving force that is accumulated. This leads to about 50 vol.% of the retained austenite grains having both lamellar and equiaxed morphologies after IA, with the latter having a wide and almost evenly spaced size distribution. In-situ synchrotron X-ray examination revealed that about 40 vol.% of the retained austenite grains could transform to martensite in a sustainable way during deformation because they had a range of mechanical stability owing to their different morphologies and wide size distributions. Moreover, the partitioning of the solute elements during IA leads to some austenite grains having proper values of stacking fault energy using which they can twin during deformation. Finally, the retained austenite grains in the medium-Mn steel can either transform to martensite gradually or twin during deformation, and contribute to large elongation at high strengths via both TRIP-assisted and TWIP effects. [ABSTRACT FROM AUTHOR]

The microstructural evolution, phase constitution and mechanical properties of directionally solidified Mg-5.5Zn-xGd (x = 0.8, 2.0, and 4.0) alloys were firstly investigated under G = 30 K/mm at a wide range of V (10 μ m/s - 100 μ m/s). It was confirmed that there existed α (Mg) + I(Mg 3 Zn 6 Gd) in Mg-5.5Zn-0.8Gd alloy, and α (Mg) + I(Mg 3 Zn 6 Gd) + W(Mg 3 Zn 3 Gd 2 ) in Mg-5.5Zn-(2.0, 4.0)Gd alloys, respectively. The criterion growth rate for cellular-columnar dendrite transition (CDT) for Mg-5.5Zn-xGd alloys decreased with the increase of Gd content. The relationships between the microstructural parameters ( λ 1 , λ 2 ) and V for Mg-5.5Zn-xGd alloys were established using a linear regression analysis. The values of λ 1 and λ 2 decreased exponentially with the increase of V and the exponent values were found to be close to the theory values of 1/4 and 1/3, respectively. The tensile test showed that the room temperature ultimate tensile strength (UTS) increased and the elongation decreased with the increase of the growth rate for a certain composition of Mg-5.5Zn-xGd alloy. For a certain growth rate, UTS first increased from 0 wt % to 2.0 wt % of Gd content, and then decreased with the further increase of Gd content. The directionally solidified Mg-5.5Zn-2.0Gd experimental alloy showed the maximum ultimate tensile strength. [ABSTRACT FROM AUTHOR]

A new high-strength Mg-6Zn-4Al-0.5Cu alloy was fabricated by direct squeeze casting and the effects of applied pressure on the microstructure and mechanical properties of the squeeze-cast alloy were systematically investigated. The results showed that the squeeze-cast Mg-6Zn-4Al-0.5Cu alloy exhibits finer and much more uniform microstructure compared with gravity-cast one, but increasing the applied pressure doses not result in further grain refinement. The porosities are decreased markedly with increasing applied pressure and eventually disappear when the applied pressure is 90 MPa. The ultimate tensile strength and elongation of the alloy are obviously improved with the application of pressure, which is mainly attributed to the full density of the samples. In addition, the strength is further improved significantly after heat treatment. When the applied pressure is 60 MPa, the heat-treated Mg-6Zn-4Al-0.5Cu alloy exhibits the optimal tensile properties with the yield strength, the ultimate tensile strength and elongation of 216 MPa, 337 MPa and 12%, which are improved by 66%, 20% and 13% respectively as comparing with that of the as-cast sample. [ABSTRACT FROM AUTHOR]

Cu-coated diamonds reinforced Cu matrix laminated composites were successfully prepared by combining flake powder metallurgy and vacuum hot press sintering. The interface strength, mechanical properties and thermal properties of Cu-coated diamonds reinforced Cu matrix laminated composites were studied. Results show that the Cu flakes obtained by flake powder metallurgy is the key to realize the laminated structure. Cu-coated diamonds have higher dispersion and higher interfacial strength when mixed with Cu matrix due to tight bonding interface. The best compressive strength, tensile strength and thermal conductivity are obtained when the content of Cu-coated diamond is 3.0 wt%. On the one hand, the diamond particles are obviously refined to achieve fine grain strengthening; on the other hand, the laminated structure is the most obvious at this time, which can provide more heat conduction channels and thus increase the thermal conductivity. In addition, the high strength of diamond can effectively prevent crack propagation through the load transfer effect at the interface. This study provides a new idea for the preparation of functional structural materials with high mechanical properties and thermal conductivity. • The interfaces between diamond and Cu are more tightly bonded by adding Cu-coated diamonds. • Lamellar structures were successfully prepared by flake powder metallurgy and vacuum hot press sintering. • Lamellar structures enhance mechanical properties by hindering dislocation motion, fine grain and load transfer. • Lamellar structures reduce interfaces and enhance thermal conductivity. [ABSTRACT FROM AUTHOR]

We reported an investigation of the influence of B 4 C contents on microstructure and mechanical behavior of AA2024/B 4 C composites. In our work, nearly full-dense AA2024/B 4 C composites with various B 4 C contents were fabricated by plasma activated sintering. Our results indicated that the B 4 C particles exhibit a network distribution in the composites with 7.5 wt % and 17.5 wt % B 4 C particles, adjacent particles of monolithic alloy are continuous or interpenetrated among the B 4 C particles in the powder boundary region. However, for the composite with 27.5 wt % B 4 C particles, the adjacent particles of monolithic alloy are interdicted due to the formation of severe aggregations. Improving the content of B 4 C particles will increase the hardness and compressive yield strength of the composites. However, the yield strength of the composite failed to be further improved when adding too much B 4 C because of the agglomeration of the reinforcements. With the content of 17.5 wt % B 4 C, the Vickers hardness and compressive yield strength of the consolidated composites were 203.2 HV and 564 MPa, respectively. In addition, quantitative analysis of the strengthening mechanisms revealed that increasing the weight fraction of the B 4 C particles results in larger augment in dislocation strengthening and load-bearing strengthening. [ABSTRACT FROM AUTHOR]

The as-cast Ti-47Al-1W-0.5Si alloys were prepared by induction skull melting (ISM) technology under argon atmosphere. Some bars were cut from as-cast ingot longitudinally and then were directionally solidified by Bridgman solidification technique. The microstructures and mechanical properties of the as-cast and directionally solidified Ti-47Al-1W-0.5Si alloy ingots with different lamellar orientations were investigated. After directional solidification, the grain boundaries were eliminated and the lamellar orientation was nearly parallel to the growth direction. The interlamellar spacing of directionally solidified samples decreased from average 1500 nm to less than 1200 nm and the interlamellar spacing was more homogeneous. In addition, the shape of Ti 5 Si 3 transformed from short rod to strip along the growth direction, and the B2 phase disappears after directional solidification. At room temperature, the compressive yield strength of Ti-47Al-1W-0.5Si alloy increases from 573 in as-cast condition to 651 Mpa after directional solidification. The fracture mode transforms from inter-granular fracture to inter-lamellar fracture after directional solidification. [ABSTRACT FROM AUTHOR]

Abstract: Open-cell 4vol.% SiCp/AlSi9Mg composite foams with different relative densities were fabricated by the infiltration process using NaCl preforms. The distributions of SiC particles in the cell wall were observed and compressive properties and energy absorption characteristic of the foams were investigated. The results show that the yield stress and the energy absorption capacities of open-cell 4vol.% SiCp/AlSi9Mg composite foams increase with the rising relative density. And the stress–strain curves of open-cell 4vol.% SiCp/AlSi9Mg composite foams are not as smooth as that of aluminum foams due to the addition of SiC particles. The theory model used to describe the energy absorption capacity of the foams in different strain region was induced. [Copyright &y& Elsevier]

Microstructure evolution and mechanical properties of TiB 2 -CoNi cermets at different sintering temperatures were investigated. A small amount of liquid phase appeared between 1362 ºC and 1398 ºC. Solid phase sintering mainly occurred below this temperature range, while liquid phase sintering mainly occurred above this temperature range. At around 1460 ºC, dissolution and re-precipitation occurred around TiB 2 particles due to liquid phase migration. Only TiB 2 and CoNi phases were detected on XRD patterns at different sintering temperatures. As the sintering temperature increased, the relative density, fracture toughness, transverse fracture strength, and hardness of cermets increased, while their porosity decreased. The main influencing factors on the properties of cermets sintered at 1460 ºC and above were the interface bonding strength and the grain size, while the porosity was the main influencing factor for cermets sintered below 1460 ºC. • TiB 2 core-(Ti, Co, Ni)B rim structure forms through liquid phase sintering. • Completely coherent interface forms between the core and rim phase. • Amorphous CoNi layer forms at the interface of rim and CoNi binder. • Interface bonding strength and fine grain enhances strength and toughness of cermets. [ABSTRACT FROM AUTHOR]

• Direct conversion of metal oxide mixture into Al x CoCrFeNi alloys via electro-deoxidization. • Research of the effects of Al addition on the crystal structure and microstructure of powder products. • Preparation of bulk Al x CoCrFeNi alloys via vacuum hot pressing sintering process. • Evaluation of Al addition effects on mechanical property and corrosion behavior of Al x CoCrFeNi alloys. Al x CoCrFeNi high-entropy alloys with different Al contents (x in molar ratio, x = 0 – 2.0) were prepared by electrochemical process using the mixed metal oxides as the precursor. The effects of Al addition on the crystal structure, microstructure, mechanical property and corrosion behavior were investigated by XRD, XPS, SEM, FE-EPMA, universal tensile testing machine, Vickers hardness tester and electrochemical workstation. With the increase of Al contents, the crystal structure of Al x CoCrFeNi HEAs transformed from FCC to the mixed crystal structures of FCC and BCC, finally, to BCC + B2. The σ-phase was formed in Al x CoCrFeNi (x = 0.8 – 1.5) HEAs during the electrolysis deoxidization. The bulk HEAs could be prepared successfully via vacuum hot pressing sintering process. The bulk HEAs exhibit excellent ultimate tensile strength (UTS) and hardness. The hardness of the Al 0 (245.2 HV) HEA and Al 0.3 (261.2 HV) HEA was twice high of the sample prepared by arc-melting method. Compared with 304 stainless steel (304SS) and Al x CoCrFeNi HEAs prepared by other method, Al x CoCrFeNi HEAs prepared by the united process shows a comparable corrosion resistance in acid, alkali and salt aqueous solutions. [ABSTRACT FROM AUTHOR]

In this paper, a new preparation method of metal matrix composites is presented. The W/FeNiMnAlW high-entropy alloy (HEA) matrix composite materials have been prepared by a simple and efficient technology. The HEA matrix consists of a face-centered cubic (FCC) phase, an ordered body-centered cubic (BCC) phase and W 2 C phase. The volume fraction and average grain size of the reinforcing phase W particles, uniformly distributed in the microstructure of HEA matrix, are 30.9% and 13.57 µm, respectively. Good metallurgical bonding between W particle and matrix is achieved, and the formation mechanism of near spherical tungsten particles is discussed, and the density of the composites is 10.55 g/cm3. The hardness of W-phase, B2 phase and FCC phase was 681.48 HV, 533.82 HV and 286.70 HV, respectively. The yield strength (σ 0.2) of the W/FeNiMnAlW composites is 1241 MPa, the maximum compressive strength (σ max) and the maximum plastic strain (ε p) are over 2530 MPa and 15% respectively, which showed superior mechanical properties. The effective combination of FCC phase and ordered BCC phase and the uniform distribution of W particles without edges are the main reasons for its good mechanical properties. The volume wear loss and wear rate of the W/FeNiMnAlW composites are respectively 0.42 mm3 and 4.95 × 10−3 mm3/N m, and the worn mechanism is mainly adhesive wear and abrasive wear. • A simple and efficient method for high-entropy alloy matrix composites is proposed. • W/FeCrNiMnW composites prepared by in-situ reaction. • The composite had high strength and good plasticity. • The formation mechanism of near spherical tungsten particles was discussed. • Lots of W particles without sharp angle are uniform distributed in the composite. [ABSTRACT FROM AUTHOR]

• The elevated mechanical properties of high strength of 2060 Al-Li alloy were considerably influenced by LSP. • The variation of microstructure and residual stress along the depth of LSPed 2060 Al-Li alloy were studied by TEM and XRD. • The primary mechanism of LSP for improving high temperature tensile properties was established. ga1 Laser shock peening (LSP) is a promising surface technique effective to improve mechanical properties by laser modification. In this study, LSP was used to strengthen the surface of a new generation of light-weight Al-Li alloy (i.e., 2060 alloy). High-density dislocations were formed in the vicinity of precipitate phase. A residual stress of compressive state was detected on the surface. According to the tensile tests conducted at various temperatures, the strength of the alloy was improved with LSP, but simultaneously, the ductility was reduced. The fractograph on the tensile sample subjected to LSP, or as received (free of the modification by laser), was characterized by a quasi-cleavage when the tensile temperature was below 200 °C, whereas ductile fracture was considered to be a determining factor at the temperature of tension above 300 °C. Dislocation strengthening was analyzed as a primary mechanism of LSP for improving high-temperature tensile properties. Namely, this improvement was attributed to the existence of a lot of dislocations near precipitates. [ABSTRACT FROM AUTHOR]

High power impulse magnetron sputtering (HiPIMS) technology is employed to prepare HfC/a-C:H nanocomposite films in Ar/C 2 H 2 atmosphere. The gas flow rate is varied to modulate the carbon content and nanocomposite structure of the film. The correlations between the carbon content and nanocomposite structure and the mechanical properties, thermal stability and oxidation resistance of HfC/a-C:H films are investigated. Mechanical properties analysis revealed that the optimal hardness 34.8 GPa is obtained at the HfC/a-C:H film with C content of 63.6 at.%. The Young's modulus is related to the C–Hf∗ bond, which effectively toughens the film. The thermal stability of the film performs well when the annealing temperature reaches 800 °C and is gradually enhanced as the amorphous carbon content increases. Moreover, films with higher amorphous carbon content have greater potential for further hardening after annealing (from 31.8 to 38.4 GPa). The oxidation resistance of the film is governed by the synergistic effect of HfC grain size and amorphous carbon content. It is demonstrated that the two factors of fine grains and narrow mean grain separation are necessary to achieve enhanced oxidation resistance. These results may open up a new possible way to design other nc-MeC/a-C:H films for optimizing the toughness, thermal stability, and oxidation resistance. • HfC/a-C:H films with different carbon contents were prepared by HiPIMS. • The hardness of 34.8 GPa is obtained at the HfC/a-C:H film with C content of 63.6 at.%. • The thermal stability of the film performed well when the annealing temperature is as high as 800 °C. • The films with higher amorphous carbon content can be further hardened after annealing. • The oxidation resistance is governed by the synergistic effect of HfC grain size and amorphous carbon matrix content. [ABSTRACT FROM AUTHOR]

To exploit the application of silicon carbide in complex-shaped and large-scale ceramic components, graphene platelet (GPL) was chosen as the reinforcement to develop silicon carbide ceramics by reactive sintering at 1700 °C. The effects of GPL content on the microstructure, phase composition and mechanical behaviors of reaction bonded silicon carbide ceramics were studied. Bulk density of the composites decreased with the increase of GPL contents because of the agglomeration of GPL. During reactive sintering, the GPL reacted with molten silicon to form laminated reinforcement, which brought about some toughening mechanisms including crack bridging, reinforcement pullout and reinforcement delamination. At the GPL content of 1.0 wt%, the flexural strength and fracture toughness of the composites reached the peak values of 436 MPa and 5.7 MPa m1/2, respectively. Thus, this work provides a path to prepare high-performance silicon carbide ceramics by reactive sintering and graphene platelet. • Graphene platelet was chosen in the reactive sintering of SiC ceramics. • Graphene reacted with molten silicon to produced laminated reinforcement. • Step-by-step fracture by graphene improved fracture toughness of SiC ceramics. [ABSTRACT FROM AUTHOR]

A strategy utilizing carbon nanotubes (CNTs) was put forward to prepare Titanium–zirconium–molybdenum (TZM) composites, which comprised Mo–0.5Ti–0.1Zr–0.03CNTs (wt.%), via high–energy ball milling (HEBM), followed by spark plasma sintering (SPS). The microstructural evolution of the TZM composite powders and the sintered samples were characterized by X–ray diffraction (XRD) and scanning electron microscopy (SEM). Their Vickers hardness and compression mechanical properties were also investigated. Results revealed that during the HEBM of TZM composite powders, the fracture mechanism dominated the early stages, followed by the agglomeration mechanism, finally reaching the balance between the fragments and the agglomerates. An increase in milling time resulted in decreased grain size and increased lattice parameter. The changes in microstructure of the composite powders induced by ball milling improved the relative density, Vickers hardness, and yield strength. Transmission electron microscopy (TEM) showed that during long ball–milling time, a Mo–Ti–Zr solid solution formed with the addition of Ti and Zr after sintering. Second–phase particles (TiZrC2) and many dislocation lines were found in the deformed samples. • A strategy utilizing carbon nanotubes (CNTs) was put forward to preparing TZM composites via HEBM and followed by SPS. • Morphological evolution of the TZM composite powders was investigated. • The mechanical properties of CNTs reinforced TZM composites after ball milling for 25 h were the best. • Solid solution strengthening and carbide dispersion strengthening enhance mechanical properties of TZM composites. [ABSTRACT FROM AUTHOR]

Two Mg-Gd-Zn-Zr alloys (GZ100K and GZ122K) with Gd/Zn atomic ratios of 24 and 3 were prepared by spark plasma sintering (SPS) and the effect of sintering temperature on microstructures and mechanical properties of these two alloys was systematically investigated. With increasing sintering temperature, the volume fraction of β-(Mg,Zn) 3 Gd phase decreases accompanied with the grain size increasing. Besides, the normal grain growth turns into abnormal grain growth in the as-sintered GZ100K when the sintering temperature increases to 440 °C. A 14H long-period stacking ordered (LPSO) phase forms in the as-sintered GZ122K at 440–480 °C, which can delay grain coarsening. The GZ122K alloy sintered at 400 °C achieves ultimate compressive stress (UCS) of 410 MPa and yield stress (CYS) of 222 MPa. While, the GZ100K alloy sintered at 400 °C reaches the highest UCS of 386 MPa and CYS of 210 MPa. Compared with the as-cast counterparts, the increment in strength of as-sintered alloys is mainly due to grain boundary strengthening arising from the fine grains produced by SPS. • Two Mg-Gd-Zn-Zr alloys with different Gd/Zn ratios were first fabricated by SPS. • The formation of 14H-LPSO phase in GZ122K can delay the grain growth. • GZ122K and GZ100K alloys achieve maximum compressive strength sintered at 400 °C. [ABSTRACT FROM AUTHOR]

Nanostructured materials prepared by severe plastic deformation processing were puzzled by the trade-off between strength and ductility. With the synergy of boundary engineering and segregation strategy, a nanostructured Mg-3Gd (wt. %) alloy with simultaneously enhanced strength and ductility was fabricated by accumulative roll-bonding processing and subsequent annealing treatment. Based on transmission electron microscopy observations, clear evidences of Gd segregation at grain boundaries, twin boundaries, stacking faults and dislocations can be observed in annealed samples. Meanwhile, the activation of non-basal slip and intensive interaction between dislocations and Gd atoms were determined in the annealed sample after tensile testing. Boundary segregation and pinning of dislocations were considered to be the main reason for the strength enhancement, while the increase in ductility was attributed to the inhibition of premature failure by Gd segregation at twin boundaries and the activation of non-basal slip. • Strong and ductile Mg-3Gd was obtained by boundary and segregation engineering. • Gd segregation at various defects occurs in annealed ARB sample. • Strengthening arises from the interaction between Gd and non-basal dislocations. • Ductility increases due to Gd segregation at TBs and hindering of non-basal slip. [ABSTRACT FROM AUTHOR]

Ultrafine-grained CoCrFeNiMn high entropy alloy matrix nanocomposites reinforced by nanoparticles were fabricated by thermomechanical consolidation of high energy mechanically milled powders. TiO(C) nanoparticles in the CoCrFeNiMnTi 0.15 sample make the FCC matrix grains clearly finer than those in the CoCrFeNiMnNb 0.1 sample with NbC and (Cr, Mn) 3 O 4 nanoparticles (average grain size: 503 ± 184 vs 778 ± 274 nm). Quantitative analysis reveals that drag force for grain growth during consolidation in the CoCrFeNiMnTi 0.15 sample is higher than that in the CoCrFeNiMnNb 0.1 sample due to the higher Zener force from the TiO(C) nanoparticles. The microstructural difference renders the yield strength of the CoCrFeNiMnTi 0.15 sample to be almost 50% higher than that of CoCrFeNiMnNb 0.1 sample (1243 vs. 831 MPa). To elucidate this phenomenon, the strengthening mechanisms are systematically analyzed and a model considering grain boundary dislocation emission is established to account for the interaction between grain boundary strengthening and nanoparticle strengthening. This model explains the different effects of NbC, (Cr, Mn) 3 O 4 and TiO(C) nanoparticles, and estimates the yield strength better than the existing models. • CoCrFeNiMn HEA matrix nanocomposites were fabricated by powder metallurgy. • TiO(C) nanoparticles drastically increase yield strength without changing ductility. • Driving force and drag force for grain growth during consolidation are analyzed. • A model considering grain boundary/nanoparticle interactions is established. [ABSTRACT FROM AUTHOR]

Combining the advantages of composites and eutectic high entropy alloys, novel MoNbRe 0.5 TaW(TiC) x high entropy alloy-ceramic eutectic composites with high strength were successfully designed and investigated based on the computer assisted thermodynamic calculation. The MoNbRe 0.5 TaW(TiC) x composites are composed of body-centered cubic (BCC) solid solution and multi-component (MC) carbide with face-centered cubic (FCC) structure. With increasing TiC addition, microstructure exhibits an evolution from hypo-eutectic to eutectic and then to hyper-eutectic, which is explained by the solidification process analysis in calculated equilibrium phase diagram. The MoNbRe 0.5 TaW(TiC) x composites possess high strength. The MoNbRe 0.5 TaW(TiC) 1.0 fully eutectic composite has the highest compressive strength of 1943 ± 13 MPa with high yield strength of 1496 ± 17 MPa. The strengthening mechanism is contributed by the synthetic effect of second-phase and boundary strengthening. Image 1 • HEA-ceramic eutectic composites of MoNbRe 0.5 TaW(TiC) x are designed and prepared. • The calculated results agree reasonably well with the experimental results. • Eutectic structure consists of BCC phase and MC carbide with good phase interface. • Eutectic composite exhibits excellent strength. • Strengthening mechanism is combination of second-phase and boundary strengthening. [ABSTRACT FROM AUTHOR]

The deformation mechanism and mechanical properties of CoCrFeNi high-entropy alloys (HEA) processed by room-temperature rolling (RTR), cryorolling (CR) and asymmetric cryorolling (ACR) were studied. As the rolling reduction increased from 20 % to 80 %, a transition in the dislocation and twinning deformation mechanisms occurred. The cryogenic environment in rolling process can promote the activation of the twins in the HEA at a lower strain, improving the deformation efficiency. The introduction of differential speed ratio led to the finer micro-shear bands with a more uniform distribution, so that the grains were refined to a greater extent. In the ACR HEA after large deformation, the stacking faults accumulated inside the deformation twins further refined the twins along the direction of long axis. This increased the strength of ACR HEA together with Lomer-Cottrell locks and FCC/HCP boundaries, reaching the maximum value compared with CR and RTR. The ultimate tensile strength exceeded 1450 MPa, and the yield strength of ACR HEA increased by nearly 1200 MPa compared to the initial material, while it still maintained the same elongation as RTR and CR. ACR showed the best strength-ductility combination during the whole rolling deformation process. The microstructure evolution and the strengthening contribution mechanism of different rolling were discussed and calculated, and the specific mechanism of how the introduced differential speed ratio further improves the strength-ductility synergistic strengthening in CR was clarified. • CoCrFeNi HEA were prepared by RTR, CR and ACR. • UTS of ACR HEA exceeded 1450 MPa, and YS increased by 1200 MPa compared to initial material. • Introduction of differential speed ratio led to the finer micro-shear bands with a more uniform distribution. • Large quantities of SFs, Lomer-Cottrell (LC) locks and twins contribute to the strengthening effect of ACR HEA. • Undiscovered FCC-HCP phase transition in CR CoCrFeNi has been found. [ABSTRACT FROM AUTHOR]

Refractory high-entropy alloy Mo 0.5 NbHf 0.5 ZrTi is selected as the base alloy and element Si is added for preparing the (Mo 0.5 NbHf 0.5 ZrTi) BCC /M 5 Si 3 in-situ compound. The effect of Si on the microstructure and mechanical properties of Mo 0.5 NbHf 0.5 ZrTi alloy is analyzed and discussed. The base alloy has the single body-centered cubic (BCC) phase. After adding Si, the alloy is composed of one BCC phase and the intermetallic M 5 Si 3 phase with hexagonal close-packed (HCP) crystal structure. The microstructure gradually evolves from the hypoeutectic structure to eutectic structure and finally to hypereutectic structure with the increase of Si concentration. The addition of Si reduces the density and increases the hardness and strength of the base alloy due to the formation of M 5 Si 3 phase. The plasticity of Si 0.1 alloy is also improved due to the grain refinement and the weakening of the solution strengthening for the dominant BCC phase and the M 5 Si 3 phase is fine while the plasticity decreases due to the formation of more brittle M 5 Si 3 phase with a larger size as Si content increases. [ABSTRACT FROM AUTHOR]

Microstructure and mechanical properties of sand mold cast Mg–4.58Zn–2.6Gd–0.18Zr magnesium alloy after different heat treatments were investigated. As-cast alloy was composed of α(Mg) matrix, interdendritic α(Mg) + W(Mg 3 Zn 3 Gd 2 ) eutectic, icosahedral quasicrystalline I(Mg 3 Zn 6 Gd) phase and Mg 3 Gd particles within α(Mg) matrix. After solution treatment at 505 °C for 16 h, most of α(Mg) + W(Mg 3 Zn 3 Gd 2 ) eutectic dissolved into α(Mg) matrix, but a new phase, Zn 2 Zr 3 , precipitated within α(Mg) matrix. The appropriate aging treatment was done at 220 °C for 16 h, after which some dispersive fine eutectics re-precipitated along the grain boundary. Furthermore, rod-like β 1 ′ and plate-like β 2 ′ formed within α(Mg) matrix. The ultimate tensile strength, yield strength and elongation of the experimental alloy in the T6 state at room temperature were 280 MPa, 175 MPa and 7.5%, respectively. According to strengthening contribution calculation, it is revealed that both the second phase strengthening and the solid solution strengthening played important roles in improving the mechanical properties after T6 treatment. [ABSTRACT FROM AUTHOR]

Quantitative microstructure information is critical to modeling and prediction of mechanical properties of structural components. In this study, the microstructure characteristics of aged squeeze-cast AZ91 alloy were investigated using scanning electron microscopy (SEM), transmission electron microscopy (TEM), and atomic force microscopy (AFM) analyses. Particularly, a study of the three-dimensional morphology of continuous precipitation during heat treatment was carried out using a combination of TEM and AFM. The results showed that a typical precipitate consisted of three kinds of faces, namely, broad, side, and end faces. The precipitate also presented a lath-shaped morphology with lozenge ends. Combined SEM and TEM analyses revealed quantitative information on the sizes and area number densities of precipitates after aging at different temperatures with different times. In general, the length and width of precipitates increased more rapidly than thickness during aging. The area number density initially increased and then slowly decreased because of coarsening. Furthermore, a special microstructure characteristic of the non-uniform continuous precipitation during aging was investigated using electron probe microanalysis (EPMA). The relationship between hardness response and yield strength was established. [ABSTRACT FROM AUTHOR]

• Ternary W alloy W-5 V-5Ta was manufactured by MA and SPS. • W-5 V-5Ta has the ultrafine grain size and a single-phase BCC structure. • W-5 V-5Ta has better mechanical properties and He+ irradiation resistance. • The contribution of strengthening mechanisms was estimated by Hull-Petch formula. • The good irradiation resistance is caused by ultrafine grain and high strength. For ensuring W employed as the armor of the divertor component in International Thermonuclear Experimental Reactor, a ternary W alloy W-5 wt%V-5 wt%Ta was manufactured by mechanical alloying and spark plasma sintering. (V, Ta)-enriched fine grains and W-enriched grains were observed in W-5 wt%V-5 wt%Ta with a single-phase body centered cubic structure. W-5 wt%V-5 wt%Ta has an ultrafine grain size, and higher relative density, microhardness, and strength than the pure W. The strenghening mechanisms were estimated, and the results indicate that grain refinement, densification, and solid solution play the main, secondary and small strengthening roles, respectively. W-5 wt%V-5 wt%Ta has a good irradiation resistance. This good irradiation resistance has a relationship with the ultrafine grains as well as higher compressive and tensile strength of W-5 wt%V-5 wt%Ta. The damage of irradiation was quantitatively analyzed by the 3D laser scanning confocal microscope. This research work suggests that W-5 wt%V-5 wt%Ta can be applied as a potential plasma-facing material. [ABSTRACT FROM AUTHOR]

SmCo permanent magnets are used in some of the strongest permanent magnets, particularly for applications between about 200 and 550 °C. However, their brittleness limits their practical use. Improving their mechanical properties is therefore of great practical significance. Cryogenic treatment is firstly applied in SmCo permanent magnets to enhance the mechanical properties. The flexural strength has been increased by 14.3% along the weakest orientation, and the impact toughness has been increased by 7.0%. After cryogenic treatment, the intrinsic coercivity is slightly increased, and the other magnetic properties are almost unchanged, which is different from other methods to improve mechanical properties at the expense of magnetic properties. The enhancement of flexural strength and impact toughness primarily stems from a decrease in residual stress. This study provides an effective and convenient approach to enhance the mechanical properties in Sm 2 Co 17 permanent magnets without sacrifice of magnetic properties. • Cryogenic treatment is firstly applied in SmCo permanent magnets to enhance the mechanical properties. • Flexural strength increased by 14.3%, impact toughness increased by 7.0%. The magnetic properties are almost unchanged. • A convenient method to enhance the mechanical properties of Sm 2 Co 17 magnet without loss of magnetic properties is provided. [ABSTRACT FROM AUTHOR]

Reduced graphene oxide (rGO) nanosheets and ZnO filled ZnAl 2 O 4 composites (rGO/ZnO/ZnAl 2 O 4 composites) were fabricated by hot-pressing sintering process in-situ reactions for the purpose of microwave absorption applications. The effects of ZnO and rGO content on the mechanical, dielectric and microwave absorption properties were systemically investigated. The results show that the porosity and microhardness increase with increasing the absorbent content, while the flexural strength presents an opposite trend. In addition, the dielectric properties present an overall increase trend with increasing the absorbent content. Because of the favorable impedance matching and the optimal microwave attenuation, the rGO/ZnO/ZnAl 2 O 4 composite with 1 vol% rGO and 8 vol% ZnO demonstrates minimum reflection loss of –44.5 dB at 10.1 GHz and effective absorption bandwidth of 3.8 GHz in 8.2–11.8 GHz and 12.2–12.4 GHz as the thickness is 2.2 mm. The synergistic effects of interfacial polarization, dipole polarization, conductance loss, and multiple scattering result in the outstanding microwave absorption properties for the investigated rGO/ZnO/ZnAl 2 O 4 composite, which indicates their potential candidates for the microwave absorbing materials with broad bandwidth and strong absorption. • Conductive-dielectric hybrid absorbents effectively enhance the microwave absorption properties of composites. • Hot-pressing sintering process in-situ reactions was used to preparate rGO nanosheets and ZnO filled ZnAl 2 O 4 composites. • With increasing the ZnO and rGO content, the mechanical and microwave absorption properties were dramatically enhanced. [ABSTRACT FROM AUTHOR]

This study investigates the relationship between aging temperature on the precipitation behavior and mechanical properties of a gravity cast Al-5.0Mg-3.0Zn-1.0Cu (wt%) alloy. After solution treatment at 470 °C for 24 h, alloys were aged at 120, 150 and 175 °C. Upon analyzing the samples, the alloys displayed different age hardening behaviors due to the variations in aging temperature. An increase in aging temperature not only reduced the peak aging time significantly, but also changed the distribution of precipitates. Numerous GPII zones and T′ precipitates (precursors of T-Mg 32 (AlZn) 49) were homogeneously distributed within matrix at a higher aging temperature and the volume fraction of T′ precipitates increased. Tensile test results for peak-aged samples determined that both yield strength (YS) and ultimate tensile strength (UTS) increased, while elongation (EL) decreased with increasing temperature. The increase in the YS can be attributed to the higher volume fraction of T′ precipitates caused by the higher aging temperature. Moreover, the impact toughness decreased (due to a continuous decrease in EL) as the aging temperature increased. By adjusting aging temperature from 120 to 175 °C, YS increased from 377 to 451 MPa, while EL decreased from 13.8% to 5.2%. After peak aging treatment at 150 °C, the alloy appears to possess optimal mechanical properties with YS, UTS, EL and toughness being 441 MPa, 496 MPa, 9.6%, and 8.1 J/cm2, respectively. These finding suggest that there are many potential advantageous applications for this alloy within automobile components requiring high strength and toughness. Image 1 • A high strength cast Al alloy related to T′ precipitates is developed. • A higher aging temperature increases strength, but reduces EL and impact toughness. • By adjusting aging temperature can control the size distribution of precipitates. • A higher aging temperature increases the volume fraction of T′ precipitates. [ABSTRACT FROM AUTHOR]

In this work, Mg-(5, 6, 7) Al-3Ca-0.3Mn (wt.%) alloys were fabricated by permanent mould direct chill casting followed by indirect extrusion, to achieve ultrahigh strength. The microstructure and mechanical properties of these alloys were systematically investigated. While C36-(Mg, Al)2Ca was identified to be the major eutectic phase in the as-cast alloys, and a bimodal microstructure composed of fine dynamically recrystallized (DRXed) grains and coarse unDRXed grains was observed in the as-extruded alloys. The as-extruded Mg-5Al-3Ca-0.3Mn (wt.%) alloy exhibits a yield strength of 420 MPa and ultimate tensile strength of 451 MPa with an elongation to failure of 4.1%. The ultrahigh strength is mainly due to dense homogeneously dispersed Mg 2 Ca nano-precipitates, grain refinement and strong basal texture. Further Al addition substantially decreases the number density of Mg 2 Ca precipitates, causing a decrease in strength. Fracture observations indicate that the low ductility of the alloys is likely caused by non-uniform distribution of the fragmented eutectic particles. Image 1 • Mg-5Al-3Ca-0.3Mn alloy with a YS of 420 MPa is developed by hot extrusion. • Ultrafine DRXed and coarse unDRXed grains are formed in the as-extruded alloy. • Dense Mg 2 Ca nano-precipitates are homogeneously dispersed in the grains. • The mechanism of premature fracture in the as-extruded alloy is discussed. [ABSTRACT FROM AUTHOR]

Abstract This study focuses on novel refractory MoNbRe 0.5 W(TaC) x high-entropy alloy matrix composites synthesized by vacuum arc melting. The microstructure evolution, compressive mechanical properties at room temperature and strengthening mechanism of the composites with addition of TaC are analyzed and discussed. The MoNbRe 0.5 W(TaC) x composites consist of a BCC solid solution as the matrix and an eutectic microstructure (BCC and multi-component carbide (Mo, Nb, W, Ta)C phases) at grain boundaries. The lamellar eutectic structure would be formed from the decomposition of subcarbide (Mo, Nb, W, Ta) 2 C and the fully solid solubility of Re. The MoNbRe 0.5 W(TaC) 0.5 composite has the maximum failure strain of 10.25%. The MoNbRe 0.5 W(TaC) 0.5 to MoNbRe 0.5 W(TaC) 0.6 composites exhibit excellent comprehensive mechanical properties, with excellent strength and reasonable ductility at room temperature. The reinforcement mechanism of the composites is dominated by precipitation and fine-grained strengthening effect. The good ductility of MoNbRe 0.5 W(TaC) 0.5 composite is contributed to the grain refinement of the BCC matrix phase. Graphical abstract Image 1 Highlights • Novel MoNbRe 0.5 W(TaC) x HEA matrix composites with addition of TaC are produced. • Microstructure consists of BCC matrix with eutectic structure at grain boundaries. • Eutectic structure is formed by subcarbide decomposition and full solubility of Re. • Composites exhibit excellent room-temperature strength and reasonable ductility. • The good ductility is contributed to grain refinement of BCC matrix. [ABSTRACT FROM AUTHOR]

The role of cobalt addition in magnetic and mechanical properties of high intrinsic coercivity Nd-Fe-B magnets by adding cobalt element and blending micron cobalt powder was investigated. The results showed that the excellent magnetic properties of high intrinsic coercivity Nd-Fe-B magnets were obtained at the Co content of 1.5 wt%, and then the intrinsic coercivity and fracture toughness decline after blending 3 wt% micron Co powder. Blending Co powder increased the Co content of main phase grain and Nd-rich phase, and the phenomenon that the Co powder additive is in the presence of pure Co particles was not been found in the sample. Simultaneously, blending Co powder reduced the heavy rare earth content of main phase grain, and new phases containing heavy rare earth and Co were formed, such as soft ferromagnetic phase R(FeCo) 3 , the low-anisotropy phase R(FeCo) 5 and rich-B phase R 1.1 (FeCo) 4 B 4 . These phenomena lead to a decrease in the intrinsic coercivity of high intrinsic coercivity Nd-Fe-B magnets. Further investigation on the grain and grain boundary indicated that the effect mechanism of blending Co powder on magnetic properties is not the same as that of the traditional alloying route. [ABSTRACT FROM AUTHOR]

Magnesium alloys have been regarded as potential degradable biomedical materials due to their suitable mechanical properties and excellent biocompatibility. In this study, Mg-Zn alloys were fabricated by powder metallurgy and then hot extruded. The effects of Zn concentration and heat treatment on their microstructure, mechanical properties and corrosion behavior were investigated. The compression test results showed that their mechanical properties were suitable for bone tissue engineering. The corrosion behavior of Mg-Zn alloys was analyzed by immersion tests and electrochemical tests in Ringer's solution. The results revealed that the increasing Zn concentration reduced the corrosion potential but increased corrosion current because severe micro-galvanic corrosion was caused by more large-size intermetallic phases. Although solid solution treatment could reduce intermetallic phase amounts, it caused micropores on the surface. And these micropores could resulted in the pitting corrosion and reduce the corrosion resistance. Notably, aging treatment could reduce the segregation of Zn and promote the compactness and uniformity of corrosion product layer on the surface, leading to the improvement of corrosion resistance. In addition, the as-extruded Mg-6%Zn alloy (wt.%) aged for 72 h was harmless to L-929 cells in cytotoxicity test. Consequently, the as-extruded Mg-Zn alloys prepared by powder metallurgy are promising to develop to be ideal biodegradable implants for bone tissue engineering. [ABSTRACT FROM AUTHOR]

The effect of aging treatment before extrusion on microstructure and mechanical properties of Mg-6Zn-1Mn alloy was investigated. Results showed that the existence of dispersive fine MgZn 2 particles before extrusion promoted dynamic recrystallization in subsequent extrusion process and leaded to fine microstructures (grain size 1∼2 μm). The rod-shaped and plate-shaped precipitates in aged alloys transformed to fine and dispersed spherical precipitates after extrusion process. With aging and extrusion treatment, ZM61 alloy showed an outstanding tensile strength and elongation balance (YS 281 MPa, UTS 378 MPa and elongation 19.3%); compressive yield strength increased from 148 MPa to 259 MPa. The tension–compression yield asymmetry was reduced at the same time. The strengthening effect of aging treatment before extrusion in ZM61 alloy proved in this paper provided a new method for the design of relatively inexpensive high-performance magnesium alloys. [ABSTRACT FROM AUTHOR]

To address new challenges in current biomedical titanium alloys, novel binary Ti-Zn alloys with high strength, low elastic modulus, excellent corrosion resistance, and intrinsic bioactivity, were prepared via hot-press sintering. In this paper, the microstructure, mechanical properties, corrosion behaviors, and in vitro biological properties of the Ti-Zn alloys were systematically investigated. The Ti-Zn alloys mainly consist of α-Ti and Ti 2 Zn phases, in which the Ti 2 Zn phase plays a good role in precipitation strengthening, and the number gradually increases with increasing the Zn contents. All of the compressive strength, elastic modulus, and nanohardness of the Ti-Zn alloys increase first, and then decrease with increasing the Zn contents. The Ti-Zn alloys show great corrosion resistance with the polarization resistance of more than 104 Ω/cm2, and the resistance continuously increases with increasing the immersion times in SBF solution. The Ti-Zn alloys possess hydrophilic surfaces with contact angles of approximately 34° ∼60°. The concentration of Zn ions released from the Ti-20Zn alloy in 0.9% NaCl solution is much lower than that of the biosafety intake. The Ti-Zn alloys exhibit favorable cytocompatibility, which are very beneficial to the spread, proliferation, and differentiation of the MC3T3-E1 cells. The above-mentioned results suggest the Ti-Zn alloys can be promising candidates for biomedical applications. • The Ti-Zn alloys were prepared by hot-press sintering with different Zn Contents. • The Ti-Zn alloys are mainly composed of α-Ti and Ti 2 Zn phases. • The Ti-Zn alloys have high compressive strength and low elastic modulus. • The Ti-Zn alloys have excellent long-term corrosion resistance in SBF solution. • The Ti-Zn alloys have excellent cytocompatibility and biological activity. [ABSTRACT FROM AUTHOR]

Crystal structures, thermoelectric and mechanical properties of p-type PbSe-SrSe system were investigated over the full composition range. A continuous solid solution was formed in the PbSe-SrSe system. Na doping was used to modulate the carrier concentration of the system. The concentrations of Sr and Na for optimum thermoelectric performance of the system were determined to be 6% and 0.8%, respectively. The figure of merit ZT at 813 K was increased from 0.58 for non-Sr containing PbSe (with 2% Na doping) to 0.8 for Na and Sr optimized PbSe-SrSe solid solution. Then, Mn was introduced into the solid solution to further optimize the thermoelectric properties. The addition of Mn could generate nanosized particle-like Mn-rich precipitates in the matrix of PbSe-SrSe alloys and substantially reduce the lattice thermal conductivities. As a result, when half of the 6% Sr was replace by Mn, the ZT at 813 K could be further raised to ∼1.03. Furthermore, the presence of the Mn-rich precipitates could effectively strengthen the mechanical properties of the PbSe-SrSe alloys, which is favorable for the future practical applications of the PbSe materials. [ABSTRACT FROM AUTHOR]

Ultrasonic surface rolling processing (USRP) was performed on a Mg–Y–Nd–Zr alloy after equal-channel angular pressing. The result shown that the surface roughness was significantly improved, residual stress was introduced to the topmost surface, and ~450 µm gradient nanostructure (GNS) of Mg alloys was obtained after USRP treatment. The mechanism of microstructure evolution and its effect on the mechanical properties of the Mg alloy were studied in detail. There are multiple deformation mechanisms in grain refinement. In the initial stage, the coarse-grain (CG) matrix was subdivided by {10 1 ̅ 2}< 10 1 ̅ 1 > extension twins. Subsequently, the deformed grains were refined into substructures using interaction between twins, interaction between twins and dislocations, and dislocation entanglement. Moreover, the substructure contains a high density of multiple stacking faults and dislocation arrays, which can effectively block dislocation movement and promote dislocation packing. Finally, equiaxed nanograins (NGs) with high-angle grain boundaries were formed via subcrystal rotation recrystallization. With the formation of a GNS, the strength of the Mg–Y–Nd–Zr alloy considerably increased at the expense of a small amount of plasticity. The tensile test results demonstrated that the yield strength (YS) and ultimate tensile strength (UTS) of the Mg–Y–Nd–Zr alloy increased from 171.96 and 262.47 MPa to 216.06 and 330.61 MPa, respectively, and the elongation rate decreased from 20.52% to 14.65% after the USRP treatment. The YS improvement of the Mg–Y–Nd–Zr alloy after the USRP treatment was attributed to grain boundary strengthening, synergistic strengthening, dislocation strengthening, and twin strengthening. Furthermore, the microhardness of Mg–Y–Nd–Zr considerably improved after USRP treatment, and grain refinement was the primary surface strengthening mechanism of the Mg–Y – Nd – Zr alloy after the USRP treatment. The work-hardening capacity of the Mg alloy improved after the USRP treatment, and the synergistic deformation between GNS and CG matrix was the primary reason for the excellent work-hardening capacity of the Mg–Y–Nd–Zr alloy. • The gradient nanostructure of Mg alloys was obtained by ultrasonic surface rolling processing. • The microstructure evolution mechanism of Mg alloys during ultrasonic surface rolling processing was discussed in detail. • The surface strengthening mechanism of Mg alloys after ultrasonic surface rolling processing was discussed in detail. [ABSTRACT FROM AUTHOR]

In this study, Ni-Cu/SAC composite solders with different Cu contents were used as an interlayer to solder Al alloy joints at 250 ℃ for different time. The results showed that the formation and evolution of the microstructure were affected by the Cu contents. In the Ni18Cu/SAC joint, the Sn solder was completely consumed to form a solid-phase joint in 5 min. And (Cu,Ni) 6 Sn 5 was the initial phase formed from the reaction between Sn solder and the Ni18Cu skeleton. Due to the higher Ni concentration than (Cu,Ni) 6 Sn 5 phase in the Ni18Cu skeleton, the Ni atoms diffused from Ni18Cu skeleton to the (Cu,Ni) 6 Sn 5 phase and replaced the Cu atoms in it. As a result, the content of Ni atoms in (Cu,Ni) 6 Sn 5 phase increased continuously, and transformed into (Ni,Cu) 3 Sn 4 at 10 min. Phase transition also occurred in the Ni38Cu/SAC joints. However, the initial phase formed from the reaction between Sn solder and the Ni38Cu skeleton was (Ni,Cu) 3 Sn 4. Therefore, the (Ni,Cu) 3 Sn 4 phase was transformed into (Cu,Ni) 6 Sn 5 at 10 min because the Cu atoms diffused from Ni38Cu skeleton to (Ni,Cu) 3 Sn 4. On increasing the soldering time, the shear strength of the joints first increased and then decreased, the Ni18Cu/SAC joints soldered for 10 min exhibited the highest shear strength of 58.3 MPa, the shearing failure mainly happened in the composite solder layers. • Two types of Ni-Cu foam/SAC305 composite solders were used to solder Al joints. • The Sn solder was completely consumed in 5 min, forming a solid-phase joint. • A solid-phase transition occurred and the grains were refined in 10 min. • An increased Cu content could affect the formation and transition of the phases. [ABSTRACT FROM AUTHOR]

Refractory high entropy alloy TiZrHfNbTa matrix composites reinforced with in-situ nitrides were prepared by vacuum arc melting. The designed composites are composed of BCC matrix and FCC nitride phases, with a particular orientation relationship between them: 111 BCC ∥ 011 MN , 10 1 ̅ BCC ∥ 200 MN , 1 1 ̅ 0 BCC ∥ 1 1 ̅ 1 MN . The composites show enhanced strengths both at room temperature and high temperature compared with the matrix alloy and increase with the increment of N content. The ambient and elevated temperature (1000 ℃) compressive yield strength is up to 2125 MPa and 350 MPa, respectively, and decent fracture strains (>19.3%) at room temperature are maintained. The underlying strengthening mechanisms are discussed systematically, and the increase in strength is mainly attributed to the combination of dislocation strengthening, load-transfer effect and Orowan strengthening. [ABSTRACT FROM AUTHOR]

Mg–Al–Sn alloys are being developed as a new series of magnesium alloys due to their good creep resistance, ductility and high temperature properties. The Mg–Al–Sn alloys containing low Al/Sn-content may have potential as a high-ductility wrought magnesium alloy. However, the effect of composition on the microstructure and mechanical properties of wrought Mg–xAl–ySn alloys have received little attention. In the present work, Mg–xAl–ySn–0.3Mn (x = 1, 3, 6 and y = 1, 3) alloys have been prepared by hot extrusion at temperatures from 523 K to 623 K. The experimental results reveal that the yield strength of the as-extruded alloys is sensitive to Al content and extrusion temperature, but insensitive to Sn content. The yield strength increases with decrease Al content or extrusion temperatures. The Mg–1Al–ySn–0.3Mn (y = 1, 3) alloys extruded at the temperatures ≤573 K exhibit the relative higher yield strength in this paper (the yield strength exceed 250 MPa with elongation of about 20%). The relative high strength is mainly attributed to the formation of fine recrystallized grains and high fraction of coarse un-recrystallized grain regions which show strong (10-10) and (0001) textures. The orientation relationship between the precipitated Al 8 Mn 5 phase and the Mg matrix in the Mg–1Al–1Sn–0.3Mn alloy is also determined. And the strengthening mechanism of the alloys is discussed. [ABSTRACT FROM AUTHOR]

Microwave absorbing composites were designed and fabricated by using hybrid carbon based fillers (carbon black (CB) and multi-walled carbon nanotubes (MWCNTs)) as absorbent and phenylethynyl-terminated polyimide as matrix, which have superior mechanical properties and high temperature electromagnetic absorption characteristics. The well dispersion of hybrid fillers enhanced the mechanical properties of the composites due to the particle reinforcement. The complex permittivity increased with the increasing temperature in the X-band frequency from 25 °C to 400 °C. The CB linking the MWCNTs contributed to the absorbing properties. The conductance loss made a major contribution to the loss mechanism at an elevated temperature. When the content of hybrid fillers is 5 wt%, the −10 dB bandwidth is 2.2 GHz and 2.1 GHz with the thickness of 1.7 mm at 25 °C and 200 °C, respectively. Further increasing the temperature would deteriorate the absorbing properties due to the poor impedance matching. [ABSTRACT FROM AUTHOR]