•The AlxSi0.2CrFeCoNiCu1−x alloys were prepared by arc melting (Ix) and injection casting assisted by liquid nitrogen (Rx).•The x range of the Rx alloys with dual-phase structure is smaller than that of the Ix alloys.•The Rx alloys exhibited finer grain size and spinodal decomposition (SD) plates.•The Rx alloys showed higher hardness and yield stress.The influence of cooling rate on microstructure and mechanical properties of the AlxSi0.2CrFeCoNiCu1−x high entropy alloys (HEAs) were investigated. The alloys were prepared by arc melting (the Ix alloys) and injection casting assisted by liquid nitrogen (the Rx alloys). Both the phase structure of Ix and Rx alloys evolved from FCC to FCC + BCC dual-phase, and finally to a BCC phase with an increase in the Al content, and the microstructure transformed from columnar dendrite to equiaxed grain correspondingly. The x range of the Rx alloys with dual-phase structure is smaller than that of the Ix alloys. The Rx alloys also exhibited smaller grain size and spinodal decomposition plate than the Ix alloys. Additionally, because of the microstructure refinement and/or phase structure change, both the hardness and yield stress of Rx alloys were higher than the Ix alloys. The maximum increase rate presented when x = 0.6, and the minimum one presented when x = 0.4.

•The mechanical properties of the porous tungsten/Zr-based metallic glass composite during cyclic compression at different temperatures were investigated.•An in-situ high energy X-ray diffraction and a finite element modeling were used to investigate the micro-deformation behavior of the composite.•Both the temperature and the pre-deformation from the cyclic loading have great influence on the work hardening behavior of the tungsten phase.The effect of temperature on the micro-deformation behavior of the porous tungsten/Zr-based metallic glass composite was investigated during cyclic compression by synchrotron based in-situ high-energy X-ray diffraction (HEXRD) and finite element modeling (FEM). Both the metallic glass phase and the tungsten phase remained elastic in the first loading at different temperatures. The metallic glass phase also exhibits “work hardening” behavior, which is attributed to the crystallization of the metallic glass phase during deformation at high temperature. The yield strength of the tungsten phase during the second loading decreased with the increase of temperature while remained almost equal in the third loading. Both the temperature and the pre-deformation from the cyclic loading have great influence on the work hardening behavior of the tungsten phase. The influence of the pre-deformation after the second cyclic loading is greater than the influence of the temperature during the third loading.

•Dynamic hardness is obviously greater than that under static indentation.•Dynamic indentation induced severer deformation than that under static indentation.•The formation of semi-circular and radial shear bands underneath indentation tips.•Substantial shear bands and numerous shear-offsets formed in dynamic indentation.Vickers hardness and plastic deformation of Ti-based bulk metallic glass (Ti-BMG) were investigated under both static and dynamic indentations. Dynamic hardness is obviously greater than that under static indentation, which is attributed to the combination effects of energy barriers and separation of nanocrystallizations from the metallic glass during dynamic indentation. Although dynamic indentation induced more severe deformation than that under static indentation, the deformation characteristics in the two loading cases are nearly the same: both exhibiting semi-circular shear bands on the top surface and a mixture of semi-circular and radial shear bands underneath the indentation tips. The most obvious difference between the two kinds of indentations is that substantial successive shear bands accompanied by numerous shear-offsets formed in dynamic indentation while obviously less shear bands and shear-offsets formed in static indentation.

The micro-mechanical behavior of porous tungsten/Zr-based metallic glass composites with different tungsten volume fraction was investigated under cyclic compression by synchrotron-based in-situ high-energy X-ray diffraction (HEXRD) and finite element modeling (FEM). During cyclic compression, the dislocation in the tungsten phase tangled near the interfaces, indicating that the elastic metallic glass phase restricted dislocation motion and obstructed the deformation of the tungsten phase because of the heterogeneity in stress. After the metallic glass phase yielded, the dislocation tended to propagate away from the interfaces, showing the decrease of the interphase stress affected the direction of motion in the dislocations. The tungsten phase exhibited increased yield strength with the increase of cyclic loading number. Yield stress of the tungsten phase decreased with increasing the tungsten volume fraction during cyclic compression, which was influenced by the elastic strain mismatch between the two phases. The stress heterogeneity and the stress distribution difference between the two phases resulted in that the yield strength of the metallic glass phase decreased with the increase of tungsten volume fraction, and accelerated the formation of shear bands in the metallic glass phase as well as cracks in the tungsten phase. The heterogeneity in stress also excessed the interface bonding strength, inducing interface fracture near interfaces.

The effect of W volume fraction (Vf) on dynamic mechanical behavior of W fiber/Zr-based bulk metallic glass composites (Wf/BMGCs) was investigated by split Hopkinson pressure bar (SHPB) and finite element method (FEM). The yield strength increased with the increase of Vf under both quasi-static and dynamic compression, and the dynamic flow stress is obviously greater than that under quasi-static compression. The fracture strain also increased with the increase of Vf under dynamic compression, which is different from that the composite with ~70 vol% W exhibited the highest fracture strain under quasi-static compression. With the increase of Vf under both quasi-static and dynamic compression, the failure mode of the composites changed from shearing to a mixture of shearing and splitting, and lastly only splitting. High strain rate suppressed macro-shearing but promoted micro-shearing and splitting compared to that under low strain rate, which is suggested to be the reason why the composites exhibited different rules of strain rate-related fracture strain under quasi-static and dynamic compression.

•Both the HEL and spall strength increased with the increase of impact velocity.•Tensile stress induced microvoids formation, resulting in microcracks initiation.•Spallation evolution was controlled by initiation and evolution of microcracks.Plate-impact experiments were performed on Ti-based bulk metallic glass (Ti-BMG) using a single stage light gas gun. Both the Hugoniot elastic limit (HEL) and spall strength increased with the increase of impact velocity, and the average HEL was estimated to be 5.34 ± 0.26 GPa. The specimen failed by catastrophic spallation, exhibiting brittle behavior at macroscopic level but ductile behavior at microscopic level. The evolution of spallation was controlled by the initiation and evolution of microcracks. The initiation of microcracks was related to the coalescence of microvoids, tensile stress played a significant role in the nucleation of microvoids during plate-impact.

The deformation and failure behavior of a porous SiC/Ti-based metallic glass composite were investigated under uniaxial compression over a wide strain rate range (~10−5 to ~103 s−1). Both the metallic glass and the SiC phase exhibited a three-dimensional (3D) interconnected net structure. The composite showed positive strain rate sensitivity when the strain rate increased from ~10−5 to ~10−3 s−1 under quasi-static compression as well as from 1.7×103 to 3.4×103 s−1 under dynamic compression. However, the fracture strength of the composite during quasi-static compression was much greater than that during dynamic compression. The fracture mode of the composite was a mixture of shearing and axial splitting under both quasi-static and dynamic compressions; the main cracks initiated at the interface between the two phases or within the SiC phase. The SiC phase and the metallic glass phase were highly constrained by each other, leading to a complicated stress state in the composite. The composite failed earlier under dynamic compression due to the cracks being initiated and propagated more quickly in comparison with quasi-static compression.

Micromechanical behaviors of Zr-based metallic glass/porous tungsten composite under quasi-static uniaxial compression at room temperature were investigated by in-situ high-energy X-ray diffraction (HEXRD) technique based on the synchrotron source and finite element modeling (FEM). During the process of compression, the main load phase was tungsten phase until it yielded at an applied stress of 1175 MPa. Subsequently, metallic glass phase became the main load phase. The plastic misfit strain of the two phases resulted in stress concentration near interfaces between them, which accelerated the process of stress transfer from the tungsten phase to the metallic glass phase. The metallic glass phase started to yield at 1500 MPa; at that time defects weakened the mutual restriction between the metallic glass phase and the tungsten phase, leading the tungsten phase to fail or the interfaces between two phases to separate by the increasing load.

The mechanical properties of both as-cast and as-extruded Zr-based metallic glass reinforced with tungsten composites with 33, 28, and 21 vol. % of metallic glass were investigated under quasi-static compression at strain rates from 10−4 s−1 to 10−1 s−1. These two types of composites exhibited a strain rate sensitivity exponent that increased with the increase of the tungsten volume fraction. Compared to the composites with 33 and 21 vol. % of the metallic glass, the two types of composites with 28 vol. % of the metallic glass phase exhibited superior fracture energies. The in-situ compression test on the as-cast composites using high-energy synchrotron X-ray diffraction (HEXRD) revealed that the yield stress of the tungsten phase increased with a decrease in the metallic glass volume fraction. The as-cast composite with 28 vol. % of the metallic glass exhibited relatively great mechanical properties compared to the composites that contained 33 and 21 vol. % of the metallic glass. This result was attributed to the great coupling of the load distribution between the two phases and the high lattice strain in the tungsten phase.

The rate-dependent deformation of Zr38Ti17Cu10.5Co12Be22.5 bulk metallic-glass-reinforced porous tungsten matrix composites was investigated over a wide range of strain rates. The composites were examined in two forms: the as-cast composite and the as-extruded composite by extrusion. In addition to showing greater strain hardening, the as-cast composite also shows much more obvious strain rate dependence of flow stress than the as-extruded composite. Microhardness tests were performed on the tungsten and the metallic glass phase in both composites, respectively. The results from the microhardness measurements indicate that the strain rate sensitivity of the as-extruded composite is primarily a result of strain rate sensitivity of the tungsten phase.

Porous SiC/Ti-based metallic glass composite (Ti-BMGC), a new kind of composite, has significant application prospect in the field of light armor. To evaluate the dynamic mechanical response of the composite, dynamic Vickers hardness and indentation-induced deformation behavior were investigated by comparison with that under static indentation. The dynamic hardness was measured by a modified split Hopkinson pressure bar (SHPB). The dynamic hardness is obviously greater than the static hardness. The brittleness parameter under dynamic indentation is also greater than that under static indentation. Although the dynamic indentation induced more severe deformation behavior than the static indentation, the deformation and fracture characteristics in the two loading cases are nearly the same, both exhibiting extensive cracks in the SiC phase and severe plastic deformation in the metallic glass phase.

To improve thermal stability of the Al65Cu16.5Ti18.5 amorphous powder, structural modification of the amorphous powder was performed through annealing and post milling. Annealing above the crystallization temperature (Tx) not only induced nanoscale intermetallics to precipitate in the amorphous powder, but also increased Cu atomic percentage within the residual amorphous phase. Post milling induced the amorphization of the nanocrystal intermetallics and the formation of Cu9Al4 from the residual amorphous phase. Thus, a mixed structure consisting of amorphous phase and Cu9Al4 was obtained in the powder after annealing and post milling (the APMed powder). The phase constituent in the APMed powder did not change during the post annealing, which exhibited significantly improved thermal stability in comparison with the as-milled amorphous powder.

The micro-mechanical behavior of Al0.6CoCrFeNi high-entropy alloy during tensile deformation was investigated using an in situ synchrotron-based high-energy X-ray diffraction technique. The alloy consisted of face-center-cubic (FCC) and body-center-cubic-based (BCC-based) structure accompanied by a small amount of σ phase. The FCC phase yielded prior to the BCC-based phase during the tensile loading, and the BCC-based phase bore more stress partition during the plastic deformation stage in spite of only ∼23% volume fraction. A reversible deformation-induced martensitic transformation from the BCC-based phase to orthorhombic phase was observed during the plastic deformation stage. The transformation preferentially occurred in the grains with an orientation of B-[001]//loading direction and B-[110]//transverse direction. The study characterized the micro-mechanical behavior of this alloy, and the reversible martensitic transformation is believed to be beneficial to the fracture toughness of such alloys.