Abrupt irreversible transformation of rhombohedral BN to a dense form in uniaxial compression of CVD material

The behavior of rhombohedral BN has been investigated under uniaxial compre ssion along the [0001](r) texture axis of a highly textured CVD rBN materia l (thin plate sample) in a diamond anvil cell without a gasket. An abrupt m artensitic transformation of the graphite-like rBN structure to a dense cub ic BN form accompanied by a distinct acoustic emission signal has been reco rded at the sample center at a pressure somewhat above 5.6 GPa, which is an order of magnitude below the threshold pressure of the transformation unde r hydrostatic compression. (C) 1999 Elsevier Science S.A. All rights reserv ed.