Constitution of Ni rich alloys in Ni–Mo–Ta system

Abstract

An investigation has been made of the constitution of the Ni–Mo–Ta system within the range 0–100 at.-%Mo and 0–40 at.-%Ta. The data are presented mainly as isothermal sections at 1523 and 1273 K, determined primarily by electron probe microanalysis and X-ray diffraction; some data for 1173 K are also included. The phases covered by the investigation are as follows: the Ni based solid solution γ, the Mo–Ta based solid solution, and intermetallic compounds based on Ni8Ta, Ni3Ta, Ni2Ta, Ni3Mo, and NiMo. A notable feature of the equilibria is the extensive solid solubility of Mo (up to ∼11 at.-%) in orthorhombic Ni3Ta in the range 1523–1173 K. In contrast to a previous report in the literature, it has also been shown that Ni3Ta and Ni3Mo do not form a continuous series of solid solutions at 1173 K. At 1523 and 1273 K, γ enters into equilibria with the following phases: Ni8(Ta, Mo), Ni3(Ta, Mo), and NiMo. The Ni3(Ta, Mo) phase enters into equilibria with γ, Ni8(Ta, Mo), Ni2Ta, NiMo, the Mo–Ta based solid solution, and, at 1173 K, with Ni3(Mo, Ta).