Formation of Stacking Fault Tetrahedra and Diffuse Streaks along 〈111〉 in the Equiatomic Cr-Co-Ni Medium-Entropy Alloy

Abstract

Formation of stacking fault tetrahedra and diffuse streaks along 〈111〉 in the equiatomic Cr-Co-Ni medium-entropy alloy subjected to different heat-treatments and different specimen preparation methods are examined by transmission electron microscopy. Neither stacking faults nor stacking fault tetrahedra are formed simply by quenching from a high temperature due to the high energy barrier for the formation and migration of vacancies. These defects, however, are found to form by Ar⁺-ion irradiation, as abundant vacancies are continuously introduced during ion-irradiation so as to bypass the high energy barrier for the formation. Diffuse streaks along 〈111〉 are usually observed in the SAED pattern with the 〈110〉 incidence regardless of heat-treatments and specimen preparation methods, indicating the occurrence of diffuse streaks is nothing to do with the formation of stacking faults and stacking fault tetrahedra.