Determination of Critical Points of Variable Composition Beta-Solidifying TiAl-Alloy

Abstract

Temperatures of critical points for a new Russian intermetallic TiAl-alloy Ti–44.5Al–2V–1Nb–Zr/Cr–0.1Gd (at.%) are determined theoretically (using Thermo-Calc software) and experimentally taking account of Zr content variation from 0.5 to 1.5 at.% (1.2–3.5 wt.%) and Cr content from 1.5 to 2.5 at.% (2.0–3.5 wt.%). It is shown that alloy solidification proceeds through β-phase and ends within the single β-phase field. Differential scanning calorimetry curves show four peaks corresponding to high-temperature transformations (L)/(L\u2009+\u2009β)/(β), (β)/(α\u2009+\u2009β)/(α), (α)/(α\u2009+\u2009γ), and low-temperature transformations (α\u2009+\u2009γ)/(α2\u2009+\u2009α\u2009+\u2009γ) and (α2\u2009+\u2009α\u2009+\u2009γ)/(α2\u2009+\u2009γ) in Zr-containing compositions, or (α\u2009+\u2009γ)/(α\u2009+\u2009γ\u2009+\u2009β), (α\u2009+\u2009γ\u2009+\u2009β)/(α2\u2009+\u2009α\u2009+\u2009γ\u2009+\u2009β), and (α2\u2009+\u2009α\u2009+\u2009γ\u2009+\u2009β)/(α2\u2009+\u2009γ\u2009+\u2009β) in Cr-containing compositions. The predicted sequence of phase fields on phase diagram polythermal sections is confirmed by experiment and it is found that critical point temperatures for the alloy studied do not change with the introduction of up to 0.1 at.% Gd.