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In metallic glass composites (MGCs), the existence of crystalline phases causes the structures of amorphous matrix to become relatively heterogeneous near the crystalline phase, resulting in the difference of mechanical properties in micro- or nano-scale in amorphous matrix near crystalline/matrix interface. In this study, this difference was characterized by nanoindentation technology, and the pile-up height was quantitatively related to the activation volume of shear transformation zones (STZs). Molecular dynamics simulations were conducted to investigate the activation behaviors of STZs during nanoindentation process of amorphous matrix. The influences of crystalline phase on deformation behaviors of amorphous matrix near the interface in MGCs were analyzed in details. • For the interface area of MGCs, the hardnesses of interface, crystalline phase and amorphous matrix increase in turn. • The existence of crystalline phase will cause the gradient distribution of free volume away from the interface in amorphous matrix. • The relationship between the pile-up height of nanoindentation in amorphous matrix, the free volume content and the number of STZs is established. [ABSTRACT FROM AUTHOR]

Here, near α titanium alloy TA15 (Ti-6.5Al–2Zr–1Mo–1V) samples were fabricated by electron beam selective melting (EBSM) and their high-temperature tensile deformation behaviors were studied at 773K–1023K. The results show that the tensile strength decreases gradually with the deformation temperature while the yield ratio increases as temperature increases from 773K to 923K, and then decreases gradually with further increasing the temperature. The deformation mechanism of EBSM-built TA15 samples at elevated temperatures can be ascribed to work hardening caused by the increase of dislocation density, and softening caused by the recovery and recrystallization. The studied TA15 alloy exhibits obvious work hardening behaviors at both 773K and 823K, dynamic recovery occurs during tensile deformation at 873K, and dynamic recrystallization plays a dominant role at 923K–1023K. The EBSM-built TA15 samples have excellent mechanical properties at medium temperatures, and the present results are helpful for the industrial applications of EBSM-built titanium alloy components in the aerospace fields. • Near α titanium alloy Ti-6.5Al–2Zr–1Mo–1V samples were fabricated by electron beam selective melting. • The tensile properties and the high temperature deformation behavior of the EBSM-built TA15 samples were studied. • The tensile strength of the EBSM-built TA15 samples decreases gradually with the increase of deformation temperature. • Work hardening was obvious at 500 °C and 550 °C, whereas dynamic recovery and recrystallization dominate at 650 °C–750 °C. [ABSTRACT FROM AUTHOR]

Abstract: Conventional crystalline materials usually exhibit a ductile to brittle transition behaviour at low temperatures. An increase in the strength is always accompanied by a decrease in the plasticity. Here the authors report on a significant enhancement in both compressive strength and plasticity of a Ti-based bulk metallic glass (BMG) deformed at low temperatures. The ductilization of the BMG system can be evidently attributed to the formation of dense shear bands and the rotation mechanism of shear bands. The cryogenic surroundings can effectively slow down the mobility and diffusion of the atoms and consequently, suppress the nucleation and growth of nanocrystals during the deformation process, allowing the simultaneous improvement in the mechanical responses of the glassy alloy to compressive loading far below the ambient temperature. [Copyright &y& Elsevier]

Carbon nanotubes-nano-WC-Co composites were prepared by spark plasma sintering process. The preparation steps involving purified carbon nanotubes were stirred into the nano-WC-Co particles in alcohol using ultrasonic shaker, then ball milled for 60 min. The densification and grain growth behavior, the mechanical properties of the nanocomposites were investigated. Experimental results show that with small amount of carbon nanotube additions, the density of the composites can be enhanced but the grain size has marginal increase; the sintered nanocomposites combine superior hardness to toughness relationships over that of the pure nanocrystalline WC-Co cermets fabricated under the same process. The reasons for the increments can be due to the extraordinary mechanical properties of carbon nanotubes, the toughing and bonding role of carbon nanotubes occurred in the nano-WC-Co matrix, as well as the spark plasma sintering technique used. [Copyright &y& Elsevier]

Here, cold-drawing was applied to melt-extracted Cu 47.5 Zr 47.5 Al 5 amorphous alloy (AA) microwires. The structural observations and tensile deformation behaviors were studied before and after cold-drawing. The drawn wire still possesses amorphous structure. Less surface defects, higher local order degree, and greater compressive residual stress induced by cold-drawing lead to a higher tensile fracture strength and a higher reliability of the drawn wires than those of melt-extracted one. The results obtained in this paper demonstrate that the cold-drawing processing is an effective method to improve the mechanical performance of the AA wires. • Cu 47.5 Zr 47.5 Al 5 alloy wire remains its glassy structure after cold-drawing processes. • Residual stresses during drawing process lead to a local disorder-order transition. • Tensile fracture strength and reliability of the alloy were enhanced by the drawing. [ABSTRACT FROM AUTHOR]

Bulk metallic glass composites (BMGCs) reinforced with a B2-CuZr phase exhibit improved ductility. However, the relationship between the macroscopic plastic deformation of BMGCs and the microscopic strain evolution is still poorly understood. Here, we investigated the strain-field evolution of a Cu 44.3 Zr 48 Al 4 Nb 3.7 (at%) BMGC by using an in-situ digital image correlation technique during tensile deformation. The strain-field evolution in the composite containing B2-CuZr particles was analysed and compared to that in a Cu 47 Zr 48 Al 4 Nb 1 BMG. We found that a high degree of shear strain heterogeneity played a key role in the macroscale plastic deformation, which was attributed to the intrinsic structural heterogeneities. These findings have implications for the development of BMGCs with excellent tensile properties. [ABSTRACT FROM AUTHOR]

The influence of annealing temperature on microstructure evolution and mechanical properties of CoCrFeNiMn 0.75 Cu 0.25 high-entropy alloy (HEA) was systematically investigated. As the annealing temperature increases, the grain becomes coarser, Cr-rich phase precipitates, and annealing twins appear in the matrix. The low angle grain boundary (LAGB) changes to high angle grain boundary (HAGB), which reduces the strength and increases the ductility of the studied HEA. The deformation bands, grain boundaries, and triple junctions of the grains are the preferred recrystallized nucleation sites. Based on the microstructural evolution, the contribution of the Cr-rich phase, LAGBs, HAGBs, and twin boundaries to the yield strength was analyzed by the modified Hall-Petch equation. These results may provide some guidance on tailoring the microstructures and mechanical properties for superior HEAs design. • The influence of annealing temperature on the microstructure and mechanical properties of a rolled HEA was discussed. • The deformation bands, grain boundaries, and triple junctions are the preferred recrystallized nucleation sites. • The microstructural evolution, and the contribution of LAGBs, HAGBs, and TBs to the yield strength was analyzed. [ABSTRACT FROM AUTHOR]

The effects of Fe doping on the microstructure, martensite transformation and superelasticity in melt-extracted Ni 50 Mn 25 Ga 25− x Fe x ( x =1–6) microwires were investigated. The unique solidification process during melt-extraction creates the micron-sized diameter wires with small grains and semicircular cross-section. At ambient temperature Ni 50 Mn 25 Ga 25− x Fe x ( x <4) microwires are austenite phases with a cubic L2 1 structure, while microwires with x >5 are martensitic phases with seven-layered modulated (7M) structure. The results point out that martensite transformation temperatures are strongly related to Fe content due to the change of valence electron concentration ( e / a ). Reversible superelastic strains of 0.92% and 0.75% are obtained in Ni 50 Mn 25 Ga 21 Fe 4 and Ni 50 Mn 25 Ga 20 Fe 5 microwires, respectively. It is demonstrated that the temperature dependence of stress-induced martensite (SIM) stress follows the Clausius–Clapeyron relation. The temperature dependence of SIM stress in Fe-doped Ni–Mn–Ga microwires is 10.5 MPa/K. [ABSTRACT FROM AUTHOR]

Abstract: In the paper, the deformation of Ti40Zr25Ni3Cu12Be20 bulk metallic glass plate subjected to shear punching has been studied. The fractured surface of the punch-out disks consists of three characteristic zones, namely the deformation band, the fractured zone, and the burr. Vein-like patterns, river-like patterns, and the coexistence of river-like patterns plus radiating cores are found on the fractured surface as the ratio of the punch-head/die clearance to the plate thickness, i.e., the relative clearance, increases because of the changes of the stress states during shear punching. Moreover, with the increase of the relative clearance, more plastic deformation occurs, causing the increase in the height percentages of both deformation band and burr. [Copyright &y& Elsevier]

Abstract: Mg–5Y–3Nd–0.6Zr–xGd (x =0, 2 and 4wt.%) alloys were prepared by metal mould casting technique, the structures and mechanical properties were investigated. The alloys were mainly composed of α-Mg solid solution and β-phase. With increasing Gd content, Mg5RE phase increased and the grain was refined. The Mg–5Y–3Nd–2Gd–0.6Zr alloy exhibited highest ultimate tensile strength and Mg–5Y–3Nd–0.6Zr alloy showed highest yield strength at room temperature. With increasing amount of Gd, the thermal resistance was improved. The Mg–5Y–3Nd–4Gd–0.6Zr alloy exhibited highest UTS and YS at 250°C, they were about 1.27 times higher than those of Gd-free alloy, which was mainly attributed to the increase of the β-phase and Mg5RE strengthening phase. [Copyright &y& Elsevier]

Abstract: Mg–4Al–4Nd–0.5Zn–0.3Mn alloy was prepared by metal mould casting method. Microstructure, aging behavior, mechanical properties and fracture morphology of the alloy were investigated. The results showed that α-Mg, Al11Nd3, Al2Nd and Mg32(Al,Zn)49 phases were the main phases of the as-cast alloy. And the long rod-like Al11Nd3 phase was decomposed to granular Al2Nd through T6 heat treatment. The tensile strength was also enhanced by T6 treatment. The yield strength was increased by 17% and 21% at RT and 150°C, respectively. It was mainly because that the precipitates were refined through T6 treatment and this became more benefit to hinder dislocations slipping. [Copyright &y& Elsevier]

Abstract: The phase evolution in the transition region of a bulk Zr56.6Cu17.3Ni12.5Al9.6Ti4 amorphous alloy wedge-ingot upon annealing has been studied. The result shows that the primary crystallized metastable phase and the amorphous matrix were found to crystallize into different products. Concerning the solidification process, it is deduced that the understanding of the competitive relationships among the intermetallic phases and the amorphous phase can be described by the phase analyses of solidification, rather than the widespread investigations of the crystallization by annealing. [Copyright &y& Elsevier]

Abstract: A new criterion, derived according to the classical theory of nucleation and growth and the perspective of phase transformation kinetics, has been proposed for evaluating the glass-forming ability (GFA) of bulk metallic glasses (BMGs) by measuring the characteristic thermal parameters. A survey of the readily available experimental data associated with the thermal analysis of various BMG alloys show that the new criterion, defined as δ = T x /(T l − T g) (where T g, T x and T l denote the glass transition temperature, the onset of crystallization temperature and the liquidus temperature, respectively), is distinctly better than other currently used criteria, such as γ (=T x /(T l + T g)) and T rg (=T g/T l) in reflecting the GFA, which implies that the δ criterion has a much better interrelationship with GFA than γ and T rg. It is also demonstrated that the δ criterion has, exclusively, a strong ability to measure and predict the GFA of industrially important BMGs based on common metals, such as Cu and Fe. [Copyright &y& Elsevier]

The CrMnFeCoNi high-entropy alloy (HEA) exhibits higher yield strength, ultimate strength and ductility at lower temperature. To further clarify the effect of the testing temperature on microstructure evolution, in-situ synchrotron-based high-energy X-ray diffraction tensile tests were carried out from 298 K down to 123 K. The enhanced yield strength of the alloy at cryogenic temperatures can be attributed to the greater lattice distortion prior to plastic deformation. Higher strain hardening rate leads to the simultaneously enhanced strength and ductility of the studied HEA below room temperature. Both dynamic Hall-Petch hardening (twinning) and dislocation hardening provide high work hardening capacity for this alloy during the plastic deformation at cryogenic temperatures. The increased dislocation density and nano-twins at cryogenic temperatures can be attributed to the decrease in the stacking fault energy as the deformation temperature decreases. These studies could provide an in-depth understanding for the strengthening mechanisms of the HEA in different temperature conditions and guide the exploration of HEAs with superb mechanical properties at cryogenic environments. • CrMnFeCoNi HEA exhibits good mechanical properties at cryogenic temperatures. • Enhanced yield strength of the alloy stems from the larger lattice distortion. • High dislocation density and nano-twins lead to the high SHR. • Lower deformation temperature pronouncedly decreased SFE. [ABSTRACT FROM AUTHOR]