Characterization of a New Microstructure in a β-Solidifying TiAl Alloy after Air-Cooling from a β Phase Field and Subsequent Tempering

Author： Chen Yi Cheng Liang Sun Lingyan Lu Yalin Yang Guang Kou Hongchao Bouzy Emmanuel

Publisher： MDPI

E-ISSN： 2075-4701|8|3|156-156

ISSN： 2075-4701

Source： Metals, Vol.8, Iss.3, 2018-03, pp. : 156-156

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Abstract

In this study, we found that well-developed α₂′ martensite was formed in a Ti-40Al-10V (atomic percent or at.%) alloy after air-cooling from a β phase field, rather than the traditional α₂/γ lamellar colonies. The martensitic laths were produced according to the Burgers orientation relationship (OR), the same as those during quenching. Local variant selection detected that three (or six) α₂′ variants sharing one (or two) common [11.0]_α2′ axes were predominant, while no global variant selection was observed. Subsequent to the martensitic transformation, the retained β phase was decomposed mainly via a β→γ transformation. The γ laths always nucleated at the α₂′/β interface according to a Blackburn orientation relationship. In order to stabilize the microstructure, the air-cooled samples were tempered at 800–1000 °C. During tempering, the microstructure decomposed mainly via an α₂′→γ transformation. The martensite was almost completely transformed after tempering at 1000 °C for 4 h, and hence a fine β-γ microstructure was obtained. Such a treatment resembling the quenching–tempering in steels may be a new strategy for the microstructural design of TiAl alloys, while an unexpected quenching process can be avoided.