GRAIN-GROWTH MECHANISMS IN A SPRAY-FORMED NI3AL AL2O3 COMPOSITE IN THE PRESENCE OF A LIQUID-PHASE/

Grain growth in the two-phase (liquid + solid) region of Ni3Al reinfor ced with 0.8 vol.% Al2O3 particulates synthesized by a spray atomizati on and co-injection technique was investigated. The grain growth of th e as-sprayed and hot isostatically pressed (HIPed) materials in the tw o-phase region was found to be consistent with cube law kinetics, i.e. , grain growth exponent was approximately 3. The activation energy for grain growth for the as-sprayed material was determined to be 308 +/- 19 kJ mol(-1) while that of the HIPed material was calculated to be 3 27 +/- 23 kJ mol(-1). The activation energy for grain growth was not a function of the amount of liquid phase or the composition of the liqu id. Furthermore, the activation energy for grain growth was higher tha n that for diffusion through the liquid phase, suggesting that the mec hanism for grain growth of the as-sprayed and HIPed Ni3Al composite in the two-phase region was controlled by an interface reaction. The rol e of the second-phase Al2O3 particles on grain growth for the as-spray ed and HIPed Ni3Al materials was not significant. (C) 1997 Elsevier Sc ience S.A.