A Novel Composition Design Method for Beta-Gamma TiAl Alloys with Excellent Hot Workability
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Beta-gamma TiAl alloys are promising light-weight structural materials for use in high-temperature applications. Disordered β phase at high temperature is beneficial to the hot workability of the alloys, while ordered β0 phase at room temperature is detrimental to the ductility of the alloys. However, we have not yet found a better way to quantitatively control β and β0 phase, which is key to improving the mechanical properties of beta-gamma TiAl alloys. In this paper, the effects of various β stabilizers on the contents of β0 and β 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 β0 phase content. Microstructural observations show that no β0 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, β 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.
The authors gratefully acknowledge the support from the National Natural Science Foundation of China (Project No. 51471056 and No. 51704174) and the State Key Laboratory for Advanced Metal and Materials foundation (Project No. 2016-ZD01) and Shandong Natural Science Foundation (No. ZR2018BEE020).
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