Formation Mechanism of B2 Phase and Micro-Mechanical Property of Rapidly Solidified Ti-Al-Nb Alloy
Received date: 2021-07-02
Revised date: 2021-12-15
Online published: 2022-01-26
Supported by
National Natural Science Foundation of China(51734008);National Natural Science Foundation of China(51871185);National Key Research and Development Program of China(2018YFB2001800)
Ti-Al-Nb alloys are widely used in the aerospace industry and are promising candidate materials for turbine engines owing to their relatively low density, high specific strength, and good oxidation resistance. Here, the effects of the cooling rate and undercooling on phase constitution, microstructure evolution, B2 phase formation, and micromechanical properties of the rapidly solidified Ti75 - x Al x Nb25 (x = 22, 45, atomic fraction, %) alloy were investigated. With a decrease in the droplet diameter, the primary B2 phase of Ti53Al22Nb25 alloy transforms from coarse dendrite to equiaxed grain under free fall. For the rapidly solidified Ti30Al45Nb25 alloy droplet, the nucleation and growth of the B2 phase transforms from the center of the γ dendrite to γ-grain boundaries, and the volume fraction of the B2 phase decreases with the droplet diameter. Under the condition of arc melting and vacuum suction casting (VSC), with an increase in the cooling rate, the average diameter of the B2 dendrite of the Ti53Al22Nb25 alloy decreases from 515 to 370 μm. For the Ti30Al45Nb25 alloy, the solidified microstructure changes from irregular (γ + B2) lamellae to regular (γ + B2) lamellar, to acicular (γ + B2) microstructure, and Al segregation is inhibited. The microhardness of Ti75 - x Al x Nb25 alloy increases with a decrease in the droplet diameter, and the maximum microhardness of each alloy is 11.57 GPa and 7.7 GPa, respectively, which are 64% and 22% higher than that of VSC, respectively, thereby indicating that the coupled effect of a large cooling rate and high undercooling can effectively enhance the microhardness of the Ti-Al-Nb alloy.
Chen LIANG , Xiaojuan WANG , Haipeng WANG . Formation Mechanism of B2 Phase and Micro-Mechanical Property of Rapidly Solidified Ti-Al-Nb Alloy[J]. Acta Metall Sin, 2022 , 58(9) : 1169 -1178 . DOI: 10.11900/0412.1961.2021.00272
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