Impact and Hot Corrosion Properties of Levitation-Melted NiAl Polycrystals with Different Purity

Abstract

Higher and lower purity NiAl polycrystals with the different levels in impurities were produced by levitation melting, and they had larger or smaller grain. The hardness in grains decreased linearly with increase in temperature up to 900–1100 K, and the lower purity alloys showed its higher value. The impact value increased as the temperature was raised, regardless of the kinds of alloys. The rate of increase in the impact values decreased above the critical temperature depending on the kinds of alloys. The critical temperature meant one showing the maximum value of the maximum load. The fracture mode was predominantly transgranular and intergranular ones below and above the critical temperature, respectively, although there was a mixture of both fracture modes regardless of test temperatures. The impact values decreased as the grain size increased at 293 K, regardless of the purity of alloys. In contrast, at 1373 K, the effect of grain size on the impact values was smaller, but the impact values of the higher purity alloys were 1.3 times-higher than those of lower purity alloys. There was no difference in oxidation behavior at 1373 and 1473 K among experimental alloys. The hot-corrosion weight loss increased in the alloys with the lower purity and smaller grains. [doi:10.2320/matertrans.48.195]