Experimental Confirmation of Ni5Al3 Phase in Ni-Al Binary System by Diffusion Couple Technique

Abstract

The equilibrium phase relationships and compositions of Ni - 51at.%Al/Ni - 26at.%Al diffusion couple heat treated at 650 °C for various times have been investigated by means of diffusion couple technique. Experimental results showed that Ni5Al3 phase was not only stable at 650 °C, but also had a large solubility range (45.3～40.6) at.% Al. The obtained relationships of NiAl/Ni5Al3 and Ni5Al3/Ni3Al are in accordance with the current generally accepted Ni-Al binary system phase diagram, but their composition ranges are quite different from the presently accepted one, that is, the the phase boundaries of NiAl / (Ni5Al3 + NiAl), (Ni5Al3 + NiAl) / Ni5Al3 and Ni5Al3 / (Ni3Al + Ni5Al3) significantly shift to the Al-rich side.