No abstract

No abstract

This study reports the effect of phase distribution on crack propagation in a dual phase AlCoCrFeNi high entropy alloy under tensile loading. The alloy is characterized by the presence of a brittle disordered BCC phase that can be toughened by precipitation of a ductile FCC phase during homogenization heat treatment. The stress and strain partitioning between the two phases is of paramount importance to determine the mechanical response of this alloy. The as-cast alloy was subjected to homogenization at 1273 K for 6 hr to prevent the formation of detrimental sigma phases and to precipitate the ductile FCC phase. In-situ tensile test in a scanning electron microscope with an electron backscatter diffraction facility was carried out to understand the micro-mechanisms of deformation of the alloy. Precipitation of the FCC phase at the BCC grain boundaries reflected the effect of the FCC phase on crack deflection and branching during propagation. The strain partitioning between the two phases and the evolution of misorientation distribution was investigated. It is observed that the presence of ductile FCC high entropy phase can impart good room temperature ductility to the brittle BCC phase. The investigation on the dual phase HEA is very few. Therefore, proper microstructural design can be utilized to toughen the brittle HEAs.

The present study aims to understand the evolution of textural and microstructural heterogeneity and its effect on evolution of mechanical properties of an equiatomic FCC CoCuFeMnNi high entropy alloy (HEA) disc subjected to high pressure torsion (HPT). HPT was performed on disc specimen with a hydrostatic pressure of 5 GPa for 0.1, 0.5, 1 and 5 turns at room temperature diffraction analysis shows decrease in crystalline size with simultaneous increase in dislocation density for five-turn HPT sample with increasing strain from centre to the periphery of the disc.Microstructural analysis using electron back scatter diffraction and transmission electron microscopy indicates extensive grain fragmentation (≈ 55 nm at the periphery of five-turn sample). The evolution of hardness from centre to the periphery of the disc cannot be explained only on the basis of evolution of grain size and dislocation density. The increase in contribution from solid solution strengthening due to partial dissolution of copper rich nano-clusters is expected to be the underlying cause for increase in the hardness. Thus, evolution of gradient microstructure, texture, and chemistry opens up new vistas for designing functionally graded materials for engineering materials.

No abstract