Oxidation behaviors of two phase NiAl+Ni3Al intermetallic compounds

Abstract

Improvement of toughness of the brittle intermetallics was reported by controlling the morphologies of the Ni3Al phase through the solution and aging treatment in two phase NiAl+Ni3Al alloy. In this work, oxidation behaviors of two phase NiAl+Ni3Al intermetallic compounds were studied while paying special attention to the early stage oxidation behaviors as well as to the effect of boron addition. Experimental results from oxidation testing at 1100 °C in air flowing at the rate of 70cc/min showed that both types of intermetallic compounds with and without boron addition showed general parabolic oxidation behavior, but addition of boron to the two phase NiAl+Ni3Al intermetallic compounds deteriorated the oxidation resistance. The differences in the oxidation resistance between the intermetallic compounds with and without boron addition could be attributed to the microstructural difference, in that an accelerated oxidation along the thin layer of Ni3Al at the grain boundary observed in the Ni-32at.%Al-0.5at.%B intermetallic compound was responsible for the poor oxidation resistance, compared with the Ni-32at.%Al intermetallic compound showing no grain boundary Ni3Al phase. In the early stage, quite complex oxidation behaviors involving several types of oxide such as NiO, NiAl2O4, Θ-Al2O3, α-Al2O3 phases were observed, depending upon the location at the grain boundary regions in the Ni-32at.%Al-0.5at.%B intermetallic compound.