The Equilibrium Diagram of the Ti-Al System

Abstract

The titanium-rich side phase diagram of the Ti-Al system has been re-examined. Electrical resistance measurements, X-ray analysis and microscopic observations were carried out to determine the equilibrium relations among the inter-solid phases. A partial phase diagram up to 50% Al by weight was constructed as shown in Fig. 16. The Al-saturated α-Ti solid solution exists conjugately with the α2 phase for the temperature range below 1020°C, at which temperature a peritectoid reaction, β-Ti+α2{\rightleftharpoons}α-Ti, takes place. The α2 phase exists in the range from 19 to 25% Al by weight and it corresponds to Ti2Al. One new phase named δ has been assumed to exist in the composition range from 26 to 34% Al by weight at high temperatures. The non-variant reactions in the solid alloys of this system were determined as follows; Composition Name Reaction Ti% Al% Temperature °C Peritectoid β-Ti+δ{\rightleftharpoons}α2 78 22 1300 to 1400 Peritectoid β-Ti+α2{\rightleftharpoons}α-Ti 92 8 1020 Eutectoid δ{\rightleftharpoons}α2+γ 73.5 26.5 1050