Microstructures and compressive properties of Ir-15Nb refractory superalloy containing nickel

Abstract

Ni-based superalloys are among the most well known and successful materials in the history of the aeronautics and gas turbine industries. These superalloys exhibit a high and almost constant yield stress with increasing temperature, until a critical temperature is reached, above which the yield stress drastically decreases. Improving this critical temperature becomes increasingly difficult due to the low melting point of base nickel (Ni). Recently, the authors proposed a new class of refractory superalloys based on platinum group metals that are potentially useful at ultra-high temperatures, at which Ni-based superalloys can not be used. These refractory superalloys have coherent fcc and L1{sub 2} two-phase structures, higher melting temperature, and superior oxidation resistance. Preliminary results show that, of these refractory superalloys, Ir-15Nb was superior in high temperature strength and oxidation resistance. However, iridium (Ir) makes this refractory superalloy dense and expensive. Now, the challenge is to replace as much Ir as possible in Ir-15Nb, while still retaining its desirable properties. Ni is completely miscible with Ir in Ir-Ni binary alloy systems. In this study, the authors determined the effects of replacing Ir with Ni in Ir-15Nb by examining the compressive properties and microstructures of several Ir-15Nb-XNi alloys.