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 reinforced with 0.8 vol.% Al2O3 particulates synthesized by a spray atomization and co-injection technique was investigated. The grain growth of the as-sprayed and hot isostatically pressed (HIPed) materials in the two-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 327 +/- 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 liquid. Furthermore, the activation energy for grain growth was higher than that for diffusion through the liquid phase, suggesting that the mechanism for grain growth of the as-sprayed and HIPed Ni3Al composite in the two-phase region was controlled by an interface reaction. The role of the second-phase Al2O3 particles on grain growth for the as-sprayed and HIPed Ni3Al materials was not significant. (C) 1997 Elsevier Science S.A.