Microstructural Refinement of α Solidified TiAl Alloy

Author of the article:GAO Wenqiang1,2, LIU Chuan1,2,3, CHU Yudong1,2, TAN Chao4

Author's Workplace：1. Innovation Center NPU Chongqing, Chongqing 401135, China; 2. Sanhang Advanced Materials Research Institute Co., Ltd., Chongqing 401135, China; 3. School of Aeronautics, Northwestern Polytechnical University, Xi'an 710072, China; 4. School of Materials Science and Engineering, Northwestern Polytechnical University, Xi'an 710072, China

Key Words：TiAl alloy; lamellar microstructure; cyclicheat treatment; grain refinement; mechanical properties

Abstract：The laminated TiAl-based alloy (Ti-47Al-7Nb-2.5V-1Cr, atomic percent) has been known as a candidate material to replace Ni-based superalloys at 650~900 ℃ due to their low density and excellent high temperature properties. In this paper, a novel method of refining the lamellar structure in TiAl-based alloys by the combination of hot isostatic processing and cyclic heat treatment is proposed. The results show that the microstructure of the TiAl-based alloy is not evenly distributed after hot isostatic pressure treatment, but its grains are further refined. Afterwards, the lamellar size of TiAl-based alloy is relatively large, up to millimeters, after single heat treatment (HT1). Nevertheless, almost all equiaxed γ phase can be obtained after double temperature heat treatment (HT2: 1 200 ℃/20 min→1 000 ℃/20 min). Moreover, the lamellar structure of the TiAl-based alloy is refined after 3 cyclic heat treatment, and its size ranges from 50 to 80 μm, of which the mechanical properties are significantly improved compared with those of the single stage heat treatment.