In-situ study of crack initiation and propagation in a dual phase AlCoCrFeNi high entropy alloy.

This study reports the effect of phase distribution on crack propagation in a dual phase AlCoCrFeNi high entropy alloy (HEA) 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 h 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. As there are very few investigations performed on the dual phase HEAs, a proper microstructural design can be be achieved and can be utilized to toughen the brittle HEAs. [ABSTRACT FROM AUTHOR]