Transformation-induced plasticity and cascading structural changes in hexagonal boron nitride under high pressure and shear

In situ x-ray diffraction study and modeling of the degree of disorder, s, and phase transformation (PT) in hexagonal hBN were performed. It was proven that changes in s are strain-induced and that s can be used to quantify plastic strain. During the strain-induced hBN --> wurtzitic wBN PT, the transformation-induced plasticity (TRIP) was exposed and quantified. TRIP exceeds conventional plasticity by a factor of 20. Cascading structural changes were revealed. Strain-induced disorder explains why PT under hydrostatic and nonhydrostatic conditions started at the same pressure similar to 10 GPa. For the same disorder, plastic shear reduces PT pressure by a factor of 3-4. (C) 2005 American Institute of Physics.