Micropillar compression deformation of single crystals of Mo5SiB2 with the tetragonal D8l structure

Abstract

The deformation behavior of single crystals of Mo5SiB2 (so-called T2 phase) with the tetragonal D8l structure has been investigated by micropillar compression at room temperature as a function of crystal orientation and specimen size. The dissociation scheme and glide plane (actual atomic layers) of the identified dislocations have been investigated both experimentally through atomic-resolution scanning transmission electron microscopy imaging of their core structures and theoretically by first-principles calculations of the relevant generalized stacking fault energy curves. Although plastic flow is observed only above 1500 °C even for single crystals in the bulk form, plastic flow is observed at room temperature in a wide range of crystal orientation in the micropillar form, and three different slip systems, (001)<100>, {110}<11¯0> and {01¯1}<111>, are identified to be operative in Mo5SiB2 at room temperature. Although (001)<100> slip was predicted by calculation in the past, the other two slip systems are identified for the first time. The values of critical resolved shear stress (CRSS) for the three slip systems are extremely high all exceeding 2 GPa. The CRSS value for each slip system increases with the decrease in the specimen size, following the inverse power-law relationship with an exponent much smaller than those reported for FCC and BCC metals. The <100> dislocation on (001) and the <11¯0> dislocation on {110} are observed to dissociate into two collinear partials on their slip plane, while the 1/2<111> dislocation on {01¯1} does not make any apparent dissociation, all of which are consistently confirmed by experiment and theoretical calculation.