Growth and healing of voids at grain boundary during high temperature creep

This paper discusses the vacancy- level variation of the volume of an isolated void located at the grain boundary under high-temperature creep and describes the kinetics of the process under predominant action of grain-boundary flows. The behaviour of a void ensemble at the grain boundary during annealing is analysed for a load normal to the grain plane and for the case of no load. It is shown that voids can grow and head independently of one another,'or heal and coalesce in. accordance with the ratios of the bulk and grain-boundary diffusion coefficients and geometry of the void ensemble. The results obtained were checked using vacuum diffusion-welded nickel joints. The specimens contained voids located within a plane-oriented grain boundary. The void behaviour at the boundary under high-temperature creep anti during annealing with no load can be adequately described using the general vacancy mechanism of mass transfer. At temperatures above 800 degrees C the voids of the ensembles examined grew and healed without coalescing. At lower temperatures, coalescence began to show its effect. Coalescence predominated in a void ensemble with the average size a = 1.1 x 10(-4) cm and the average spacing L = 10(-4) cm during annealing at T = 600 degrees C.