Nickel-aluminum-molybdenum phase equilibria

Abstract

Recent work on alloys based on the Ni-Al-Mo system has brought to light several inconsistencies with published equilibrium phase diagrams for this system. Published diagrams have been based on theoretical computer models and on data gathered ostensibly before equilibrium was achieved, especially at temperatures below 1100 °C. The intent of this effort was to produce an experimentally validated ternary equilibrium phase diagram for the Ni-Al-Mo system. Specimens for this task were produced by both conventional casting and powder metallurgy techniques. The temperatures studied included 1260, 1171, 1093, 1038, and 927 °C (2300, 2140, 2000, 1900, and 1700 °F) for times up to 2500 hours. Phases were identified using an electron probe microanalyzer and X-ray diffraction. The results show significant deviations from the proposed phase diagrams published in the literature in the temperature range investigated. In particular, a class II four-phase equilibrium reaction γ + α cooling // heating γ′+ δ has been shown to occur at 1127 ± 2 °C (2060 ± 4 °F).