A Novel Composition Design Method for Beta-Gamma TiAl Alloys with Excellent Hot Workability

摘要

Beta-gamma TiAl alloys are promising light-weight structural materials for use in high-temperature applications. Disordered beta phase at high temperature is beneficial to the hot workability of the alloys, while ordered beta(0) phase at room temperature is detrimental to the ductility of the alloys. However, we have not yet found a better way to quantitatively control b and beta(0) phase, which is key to improving the mechanical properties of beta-gamma TiAl alloys. In this paper, the effects of various b stabilizers on the contents of beta(0) and b phase were investigated. A quantitative composition design method for beta-gamma TiAl alloys was proposed. A room-temperature Mo equivalent ([Mo](eq-RT)) was developed to estimate beta(0) phase content. Microstructural observations show that no beta(0) phase will precipitate in TiAl alloys when the value of [Mo](eq-RT) is below 1. A high-temperature Mo equivalent ([Mo](eq-HT)) was introduced to evaluate the hot workability of TiAl alloys. The relationship among alloy composition, beta phase content, and hot workability was constructed. Isothermal compression tests indicate that the hot workability of TiAl alloys can be significantly improved when [Mo](eq-HT) reaches above 1.3. The validity of [Mo](eq-RT) and [Mo](eq-HT) were verified by actual experiments. Two equivalence formulas provide important guidance for the composition design of beta-gamma TiAl alloys. (C) The Minerals, Metals & Materials Society and ASM International 2018.