Kinetics of densification and grain growth in ultrafine WC-Co composites

Dilatometer densification measurements were performed on WC-Co composites containing 2, 5 and 10 wt% Co. The runs were carried out under a flow of 10% H-2-Ar up to 800 degrees C followed by vacuum up to 1400 degrees C. Analysis of diffusional densification kinetics suggest an initial solid state densification from 800 to about 1190 degrees C attributed mainly to grain growth-densification indicated by acceptable fittings to a modified Coble intermediate stage model. This behavior was confirmed by grain growth analysis (range 820 to 1400 degrees C) measured in fractures surfaces of partially densified pellets. It was detected either a softening solid state stage or eventually liquid formation at similar to 1150-1200 degrees C and a kind of viscous flow densification behavior operating prior to apparently the solution precipitation liquid phase sintering. The densification model for diffusional liquid phase sintering applied well in the 1260-1400 degrees C range with 105-150 kcal mole(-1) activation energy depending on Co content. The standard rearrangement stage was also valid partially within the temperature range 1320 to 1400 degrees C. Certain fittings of present densification data using phenomenological continuous mechanics approach were carried out, obtaining activation energies ranging between 6 and 35 kcal mole(-1). Although no clear assignments of such values to probable matter diffusion processes could be made, it is noted the latter value (35 kcal mole(-1)) is close to the 25-36 kcal mole(-1) values obtained for the classical liquid rearrangement stage. (C) 2016 Elsevier Ltd. All rights reserved.