Elastic and plastic properties of as-cast equimolar TiHfZrTaNb high-entropy alloy

Abstract

Elastic properties of as-cast TiHfZrTaNb high entropy alloy were investigated by ultrasound measurements, yielding G=C44=28GPa and C11=172GPa effective isotropic elastic constants, allowing computation of the Young’s modulus E, the bulk modulus B and Poisson ratio ν of about 78.5GPa, 134.6GPa and 0.402, respectively. A Pugh ratio G/B as lower as 0.208 and high positive Cauchy pressure (C12–C44)=80GPa were calculated, suggesting a ductile behavior. Tensile tests were carried out on specimens taken along the ingot diameter to address micro-segregations effect on the macroscopic behavior. More specifically, micro-segregations were addressed at a smaller scale via nanohardness measurements. Given the observed low deviations from both tensile and nanoindentation experiments, micro-segregations influence was concluded to be negligible. The necking and fracture surface investigations revealed multiples slip bands, grains boundary distortions, mixture of shallow and profound dimples of varying sizes, all of which characterize a high tensile ductility behavior, in line with elasticity measurements prediction. Post-mortem EBSD investigations revealed lattice distortions mainly at grain boundaries vicinity as a consequence of dislocations accumulation.