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Ti-based bulk metallic glass composites (BMGMCs) containing an in situ formed metastable β phase normally exhibit enhanced plasticity attributed to induced phase transformation or twinning. However, the underlying deformation micromechanism remains controversial. This study investigates a novel deformation mechanism of Ti-based BMGMCs with a composition of Ti42.3Zr28Cu8.3Nb4.7Ni1.7Be15 (at%). The microstructures after tension were analyzed using advanced electron microscopy. The dendrites were homogeneously distributed in the glassy matrix with a volume fraction of 55 ± 2% and a size of 1~5 μm. The BMGMCs deformed in a serrated manner with a fracture strength (σf) of ~1710 MPa and a fracture strain of ~7.1%, accompanying strain hardening. The plastic deformation beyond yielding was achieved by a synergistic action, which includes shear banding, localized amorphization and a localized BCC (β-Ti) to HCP (α-Ti) structural transition. The localized amorphization was caused by high local strain rates during shear band extension from the amorphous matrix to the crystalline reinforcements. The localized structural transition from BCC to HCP resulted from accumulating concentrated stress during deformation. The synergistic action enriches our understanding of the deformation mechanism of Ti-based BMGMCs and also sheds light on material design and performance improvement. [ABSTRACT FROM AUTHOR]

From the mechanistic point of view, magnesium alloys are lightweight materials and are receiving increasing attention in the past several years in various fields. Prof. Liang Zhen from Harbin Institute of Technology, China and the United State military are showing keen interest in the development of magnesium alloys as ballistic resistant material. However, their use is still limited owing to low ductility, low formability, and average mechanical properties. The magnesium alloys components must withstand the shockwave under hypervelocity ballistic impact. The ballistic testing can produce gradient variations of the strain and stress-energy away from the crater, and useful for the development of these alloys in the military and aerospace industry. Therefore, the present review article shed light on the post deformation analysis of the Mg alloys subjected to the different projectiles under ballistic impact, and the underlying mechanisms were discussed. In the end, some important issues regarding the ballistic impact and further studies in this field were proposed.

This research reports detailed investigations on the dynamic compression properties and the deformation mechanism in Ti6321 titanium alloy subjected to high strain rate loading by using the split Hopkinson pressure bar (SHPB). Microstructures of deformed samples were analyzed by scanning electron microscopy (SEM) with an electron backscatter diffraction (EBSD) detector and transmission electron microscopy (TEM). The experimental results demonstrate that with the increase of strain rate, the strength of Ti6321 titanium alloy increases significantly, which indicates the phenomenon of strain rate hardening. Due to twinning, the initial plastic deformation mechanism is by twin shear, the twins' interface is straight, continuous, and symmetrically distributed. The majority of twins are found at low strain stage (the strain range of 0.03 ∼ 0.06), which justifies the early initiation and contribution of twins in plastic deformation of the material. It also indicates that during plastic deformation twinning dominates the dynamic deformation mechanism. As the strain (e) increases further (when the strain is greater than 0.06), the number of twins also increases up to ɛ = 0.20. After that, the dynamic deformation mechanism started shifting from twinning deformation to dislocation slip.

The ultra‐high molecular weight polyethylene (UHMWPE) fiber laminates were prepared by hot pressing at temperatures ranging from 120 to 140 °C and pressures of 15 and 25 MPa. Mechanical test results demonstrated that increasing the molding temperature improved the interlaminar shear strength, in‐plane shear strength, and bending strength of the laminates. Additionally, the in‐plane tensile properties of the laminate were influenced by both the positive effect of increased bond strength and the negative effect of reduced fiber strength. The mechanical properties of the laminate showed improvements at −50 °C but decreased at 70 °C. Low‐velocity impact tests revealed that higher molding temperature and pressure enhanced the dynamic bending stiffness and peak force while reducing the bulge in the laminate's back. Remarkably different low‐velocity impact performance was observed in the laminate at −50 and 70 °C compared to room temperature. [ABSTRACT FROM AUTHOR]

In this study ultra-fine grained single pass extruded ZK61 magnesium alloy sheet is processed at temperature 350 °C with area reduction ratio ˜30. The complex dynamic mechanical behavior is studied experimentally with Split Hopkinson pressure bar over wide ranges of strain rates (1000–4000 s−1) along the normal direction. Electron backscattered diffraction, scanning electron microscopy and optical microscopy analysis are employed to reveal the changes in texture and fracture analysis. Positive strain rate sensitivity is observed up to strain rate 3000 s−1 that is signature of basal slip and extension twinning although the grain size was very small. This finding is contradiction to experimental and theoretical predictions suggesting the elimination of twinning induced deformation in magnesium alloys in very fine small grains

The superplasticity of a fine-grained extruded ZK61 magnesium (Mg) alloy was investigated by tensile testing at various elevated temperatures and strain rates. The results demonstrated the strain rate sensitivity (m-value) ~0.51 and ~0.4 and stress exponent (n-value) ~1.96 and ~2.5 at temperatures 673 K and 623 K, respectively. The numerical simulation revealed that the activation energy (Q-value) was in the range of 92.9–146.7 kJ/mol. Therefore, the high elongation to fracture (FE) ~400% and ~334% were achieved at temperatures 673 K and 623 K under tensile loading at a strain rate of 0.001 s−1. The microstructure was thermally stable at elevated temperatures and attributed to MgZn2 phase particles. Based on m-value, n-value, FE, average Q-value ~114 kJ/mol, and thermally stable microstructure, it was found that the governing deformation mechanism was the intra-granular slip. These all feathers assisted in understanding the superplastic behavior of the ZK61 Mg alloy.

From a mechanistic point of view, eye-catching magnesium alloys are greatly different than face-centered cubic metals. However, low strength, low ductility, and anisotropic mechanical behavior of Mg alloys are main hurdles, which are mainly attributed to the hexagonal close-packed structure, limited-slip activity, low stacking fault energy, and twin strain path dependencies. The {101¯2}twin boundaries can easily be imparted in Mg alloys through in-plane compression, thereby decrease the grain size through twin boundaries grain refinement and greatly change the crystallographic texture. The twin dependencies on strain path loading and different slip activity change the mechanical strength. However, the size of the specimen before pre-compression is the most critical parameter which should be chosen wisely. Apart from this, a fraction of dislocations can also be induced by pre-compression up to strain ~7–10%. Therefore, it is anticipated that the pre-induced grain refinement through twin boundaries, textural changes, and dislocations by cross pre-compression would be advantageous for high strength, high ductility, and exacerbation of anisotropic behavior.