Process modeling, behavior and characterization of spray atomized and deposited nickel aluminide/aluminum oxide composites

The present investigation was undertaken to elucidate: (1) the criteria governing the penetration of ceramic particles into atomized droplets; (2) microstructure evolution of spray atomized intermetallics in light of numerical simulation; (3) the mechanisms of grain growth kinetics in the presence of a liquid phase of as-sprayed and HIPed Ni{dollar}sb3{dollar}Al; (4) the fracture behavior of spray atomized and deposited Ni{dollar}sb3{dollar}Al. The present results showed that Al{dollar}rmsb2Osb3{dollar} droplets can be incorporated into an intermetallic material such as Ni{dollar}sb3{dollar}Al by the use of spray atomization and deposition and that the extent of incorporation depends on the solidification condition of the droplets at the time of droplet/particle interaction. In droplets smaller than {dollar}sim{dollar}40 {dollar}mu{dollar}m, no penetration of the Al{dollar}rmsb2Osb3{dollar} particles was observed. The modeling of the thermal history showed that droplets in this size range were fully solidified at the point of co-injection. Modeling of the penetration criteria showed that penetration was not possible in fully solidified droplets. Penetration of the Al{dollar}rmsb2Osb3{dollar} particles was observed in fully liquid droplets and partially solidified droplets as long as the particles impinged the droplets on the liquid portion of the surface. It was shown that the kinetic energy of the Al{dollar}rmsb2Osb3{dollar} particles was greater than the surface energy change of the droplets which acts as the repulsive force to penetration. Consequently, the repulsive surface energy force was not a limiting factor governing the particle penetration behavior in the present system. Furthermore, it was shown that the solidification front velocity for the present system of materials was such that it engulfed or trapped the particles inside the droplets.; Modeling of the microstructure evolution revealed that the high heat extraction rate associated with the substrate area "froze" the small fully solidified droplets inside the larger droplets containing the fragmented dendrites resulting in the formation of thick prior-droplet boundaries. Furthermore, it was found that the elevated mass density at the center of the spray promotes a high degree of compaction favoring the formation of thin prior droplet boundaries and the elevated temperature anneal facilitates the growth and coalescence of dendrite fragments resulting in the formation of spheroidal grains in spray formed Ni{dollar}sb3{dollar}Al.; The grain growth of the as-sprayed and HIPed materials in the two-phase region was found to be consistent with cube law kinetics, i.e., grain growth exponent was {dollar}sim{dollar}3. The activation energy for grain growth for the as-sprayed material was determined to be 308 {dollar}pm{dollar} 19 kJ/mole while that of the HIPed material was calculated to be 327 {dollar}pm{dollar} 23 kJ/mole. 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 Ni{dollar}sb3{dollar}Al composite in the two-phase region was controlled by an interface reaction.; The tensile fracture behavior of the spray formed IC-396 was determined to be predominantly transgranular while that of the spray formed IC-50 was intergranular.