Dislocation mechanisms, diffusional processes and creep behavior in NbC x

Abstract

A brittle-ductile transition occurs around 1373 K in NbC x primarily as a result of the increase in the metal character of the bonding with increasing temperature. Steady-state creep in NbC x between 1373 and 1573 K occurs by dislocation glide to form equiaxed cell structures; it is controlled by the unlocking of dislocation interactions within the cell walls. Between 1573 and 1873 K, the kinetic data indicate a transition from dislocation glide to dislocation climb as the rate controlling creep process. Above 1873 K, subboundary formation, and polygonization confirms that dislocation glide and climb are occurring during creep. The activation energy values for creep in this temperature range are consistent with niobium lattice diffusion as the rate controlling mechanism.