Determination of Phase Equilibrium in the Ti-Rich Ti–Mo–Al Ternary System Using the X-Ray Microanalyser

Abstract

Abstract Isothermal sections from 700 to 1000°C of the Ti-rich corner of the Ti–Mo–Al ternary phase diagram were determined by analysing quantitatively the α and β phases within the two-phase field using the electron-probe X-ray microanalyser. High accuracy can be achieved with a small number of specimens and treatments, and the method is suggested as a standard procedure for ternary phase-diagram determination. The solubility of molybdenum in the α phase is 0·6–0·75 wt.- % at 700–800°C, and in α2 ∼ 1·2 wt.-%Mo. Tie lines in the α + β field were determined, their average inclination being ∼−0·07 wt.-%Al/wt.-%Mo. This is also the average slope of the α + β/α+α2 + β phase boundary, whose location was determined from the abrupt rotation of tie lines, without the limitatioll that arises in other methods. by the need to resolve the α2 phase. The boundary appears at a low aluminium content, in agreement with recent reports on the evidence of ordering in Ti-AI alloys with 6 wt.-%Al or less. A method for checking...