Z.M. Jiao

Plastic Deformation of Al0.3CoCrFeNi and AlCoCrFeNi High-Entropy Alloys Under Nanoindentation

The mechanical properties of Al0.3CoCrFeNi and AlCoCrFeNi high-entropy alloys (HEAs) were investigated by instrumented nanoindentation over a broad range of loading rates. It was found that the loading portion of the two HEAs exhibited apparent discontinuities at low loading rates. However, the discontinuity became less pronounced with increasing the loading rate. The experimental results that the hardness, elastic modulus, and yield strength of AlCoCrFeNi HEAs are larger than those of Al0.3CoCrFeNi HEAs can be elucidated in terms of thermodynamic and topological parameters of the constituent elements and solid solution strengthening, respectively. In situ scanning images displayed a significant pile-up around the indents, demonstrating that a highly localized plastic deformation occurred under nanoindentation. Furthermore, the resistance for creep behavior increases as the Al concentration is increased due to the enlarged lattice distortion related to a solution strengthening effect.

Nanoindentation characterised plastic deformation of a Al0.5CoCrFeNi high entropy alloy

Abstract The plastic deformation of a high entropy alloy Al0.5CoCrFeNi was investigated by instrumented nanoindentation over a broad range of strain rates at room temperature. Results show that the creep behaviour depends on the strain rate remarkably. In situ scanning images showed a significant pile up around the indents, demonstrating that a highly localised plastic deformation occurred in the process of nanoindentation. Under different strain rates, contact stiffness and elastic modulus basically remain unchanged. However, the hardness decreases as indentation depth increases due to indentation size effect. For the same maximum load, serrations became less prominent as the loading rate of indentation increased. Similar serrations have been observed in the current alloy upon quasi-static compression.

Superior Mechanical Properties of AlCoCrFeNiTi x High-Entropy Alloys upon Dynamic Loading

High-entropy alloys with composition of AlCoCrFeNiTix (x: molar ratio; x = 0, 0.2, 0.4) under quasi-static and dynamic compression exhibit excellent mechanical properties. A positive strain-rate sensitivity of yield strength and the strong work-hardening behavior during plastic flows dominate upon dynamic loading in the present alloy system. The constitutive relationships are extracted to model flow behaviors by employing the Johnson-Cook constitutive model. Upon dynamic loading, the ultimate strength and fracture strain of AlCoCrFeNiTix alloys are superior to most of bulk metallic glasses and in situ metallic glass matrix composites.

Dynamic Deformation Behaviors of an In Situ Ti-Based Metallic Glass Matrix Composite

Quasi-static and dynamic deformation behaviors, fracture characteristics, and microstructural evolution of an in situ dendrite-reinforced metallic glass matrix composite: Ti50Zr20V10Cu5Be15 within a wide range of strain rates are investigated. Compared with the quasi-static compression, the yielding stress increases, but the macroscopic plasticity significantly decreases upon dynamic compression. The effects of the strain rate on strain hardening upon quasi-static loading and flow stress upon dynamic loading are evaluated, respectively. The Zerilli-Armstrong (Z-A) model based on dendrite-dominated mechanism is employed to further uncover the dependence of the yielding stress on the strain rate.