On the inherent strength of Cr23C6 with the complex face-centered cubic D84 structure

Abstract

The deformation behavior of single crystals of Cr23C6 with the complex D84 crystal structure based on the face-centered cubic lattice has been investigated by micropillar compression as a function of crystal orientation and specimen size at room temperature. For the first time, the {111}<1‾01> slip system is identified to be the only operative slip system. The 1/2<1‾01> dislocation dissociates into two partial dislocations with identical collinear Burgers vectors (b) as confirmed by transmission electron microscopy (TEM) and atomic-resolution scanning transmission electron microscopy (STEM). The energy of the stacking fault bounded by two coupled partial dislocations with the b = 1/4<1‾01> is evaluated from their separation distances to be 840 mJ/m2. The critical resolved shear stress (CRSS) for {111}<1‾01> slip increases with the decrease in the specimen size, following the inverse power-law relationship with a relatively low exponent of ∼ -0.19. The room-temperature bulk CRSS value evaluated by extrapolating this inverse relationship to the specimen size of 20∼30 μm is 0.79 ± 0.15 GPa. The exact position of the slip plane among many different parallel {111} atomic planes and possible dislocation dissociations on the relevant slip planes are discussed based on the calculated generalized stacking fault energy (GSFE) curves. The inter-block layer slip is deduced to occur for {111}<1‾01> slip based on the TEM/STEM observations and the result of GSFE calculations. Finally, plausible atomic structures for stacking faults on (111) and coherent twin boundaries are discussed.