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

The deformation behavior of single crystals of Cr(23)C(6 )with the complex D8(4) 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}<101> slip system is identified to be the only operative slip system. The 1/2<101> 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<101> is evaluated from their separation distances to be 840 mJ/m(2). The critical resolved shear stress (CRSS) for {111}<101> 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 mu m 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}<101> 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.