Orientation- and size-dependent room-temperature plasticity in ZrC crystals

Using in situ electron microscopy-based nanomechanical testing, we show that sub-micron-scale ZrC(100) and ZrC(111) single crystals exhibit size- and orientation-dependent room-temperature plasticity under compression. We identify {} and {0 0 1} as the active slip systems operating in ZrC(100) and ZrC(111) crystals, respectively. For both the orientations, yield strengths increase with decreasing crystal size. ZrC(111) is found to be up to 10× softer than ZrC(100). Using density functional theory calculations, we attribute the observed anisotropy to surprisingly facile shear along {0 0 1} compared to {}. Based upon our results, which provide important insights into plastic deformation modes operating in ZrC, we expect that slip systems other than {} can be softer and operate at low temperatures in NaCl-structured refractory transition-metal carbides and nitrides.