The microstructure of a NiAl-based multiphase alloy with a composition of Ni-25Al-25Cr has been investigated, which consists of NiAl matrix surrounded by a eutectic of α-Cr, β-Ni(Al,Cr) and γ'-Ni3(Al,Cr), and a large amount of α-Cr precipitates distributed uniformly in NiAl matrix. This alloy exihibits superplasticity elongation as high as up to 480% at 1123-1223 K and strain rates of 2.2×10-4 -3.3×10-2 s-1. The fracture after superplasticity deformation results from cavities generated by grain boundary sliding and cleavage in the grains, the mechanism for superplasticity has also been discussed.
The electrical properties of Fe3Al intermetallics have been studied. The results indicate that the binary Fe3Al alloys have high electrical resistivity which relates to Al content. Additions of alloying elements further increase the electrical resistivity. An anomalous relationship between resistivity and temperature has been found in the temperature range of 20-1100℃,and the mechanism of the phomenon has also been discussed.
The oxidation resistance of the binary Fe3Al decreases rapidly with the increase of temperature when the temperature is above 1000℃. SEM observations have revealed wisker-shaped oxides on specimen surface oxidized at 1200℃. Cavities and internal oxidation have been observed between the oxidation layer and the matrix of oxidized specimen. Microalloying of Ce increases the oxidation resistance of Fe3Al based alloys significantly. After oxidizing at 1200℃ for a long time (120 h), the specimen surface of the Fe3Al alloy containing cerium is still smooth without spalling and its oxidation resistance is one order of magnitude higher than that of the alloy without cerium addition.