Investigation on Ni3Al-Ni7Hf2 unidirectionally solidified eutectic composite

The formation of a Ni3Al(gamma')+Ni7Hf2 unidirectionally solidified lamella r 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 degrees C as determined by DTA. The critical ratio of G/ R for Ni3Al+Ni7Hf2 eutectic is found to be 5 x 10(5) degrees C . s . cm(-2) , and the lamellar Ni3Al+Ni7Hf2 eutectic aligned parallel to the direction of solidification was made with R = 5 mu m/s and G = 250 degrees C/cm. The investigation shows that the lamellar eutectic has a preferred crystallogra phic orientation between the Ni3Al and Ni7Hf2 lamellae, i.e., (111)(Ni3Al)/ /(100)(Ni7Hf2) and [110](Ni3Al)//[010](Ni7Hf2). 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 degrees C/110 h. This demo nstrates that the Ni3Al+Ni7Hf2 lamellar eutectic has high interface thermal stability. (C) 1999 Kluwer Academic Publishers.