Investigation on Ni3Al-Ni7Hf2 unidirectionally solidified eutectic composite

Abstract

The formation of a Ni3Al(γ′)+Ni7Hf2 unidirectionally solidified lamellar eutectic composite has been investigated in this paper. The results show that Ni-5.8Al-32Hf alloy, which has the Ni3Al+Ni7Hf2 eutectic structure, is a suitable composition of D.S eutectic material. The melting range of this composition is 41 °C as determined by DTA. The critical ratio of G/R for Ni3Al+Ni7Hf2 eutectic is found to be 5× 105 °C · s · cm−2, and the lamellar Ni3Al+Ni7Hf2 eutectic aligned parallel to the direction of solidification was made with R = 5 μm/s and G = 250 °C/cm. The investigation shows that the lamellar eutectic has a preferred crystallographic orientation between the Ni3 Al and Ni7Hf2 lamellae, i.e., (111)NiAl//(100)NiHf and [110]NiAl//[010]NiHf. The lamellar Ni7Hf2 did not degrade or coarsen obviously, and no harmful phase formed in the interface of Ni3Al/Ni7Hf2 after long time soaking of 1100 °C/110 h. This demonstrates that the Ni3Al+Ni7Hf2 lamellar eutectic has high interface thermal stability.