Experimental Determination of γ/(γ+α₂)/α₂ Phase Boundaries in a Ni-Cr-W-Mo Quaternary System

Abstract

To determine experimentally the solubility of a tungsten-rich bcc α₂ phase in a nickel-rich fcc γ phase in a Ni-Cr-W-Mo quaternary system, four Ni-Cr-W-Mo alloys with 0.03wt pct carbon, whose compositions were in a γ+α₂ phase field, were equilibrated at 1 000, 1 100, 1 200, and 1 300°C for 8 000, 4 500, 100, and 100h, respectively. Chemical compositions of the constituent phases were determined by means of electron microprobe analysis. Tie-lines between γ and α₂ phases and γ/(γ+α₂)/α₂ phase boundaries were constructed in four isothermal sections of the Ni-Cr-W-Mo quaternary equilibrium phase diagram. The solubility of α₂ in γ decreased with decreasing temperatures. Precipitation of carbides such as M₆C and M₁₂C at lower temperatures apparently lead to further decrease in the α₂ solubility.