MICROSTRUCTURE STABILITY IN A FULLY LAMELLAR HIGH Nb－TiAl ALLOY AFTER LONG－TERM THERMAL CYCLING
FANG Lu 1), DING Xianfei2), ZHANG Laiqi1), HAO Guojian1), LIN Junpin1)
1) State Key Laboratory for Advanced Metals and Materials, University of Science and Technology Beijing,Beijing 100083
2) National Center for Materials Service Safety, University of Science and Technology Beijing, Beijing 100083
Cite this article:
FANG Lu,DING Xianfei, ZHANG Laiqi, HAO Guojian, LIN Junpin. MICROSTRUCTURE STABILITY IN A FULLY LAMELLAR HIGH Nb－TiAl ALLOY AFTER LONG－TERM THERMAL CYCLING. Acta Metall Sin, 2013, 49(11): 1416-1422.
Microstructure stability in the fully lamellar Ti－45Al－8.5Nb(W, B, Y) alloy were investigated by OM, SEM and TEM after long－term thermal cycling (500 and 1000 cyc) at 900 and 1000℃. The results showed that Al－segregation could not be eliminated completely after the heat treatment. After long－term thermal cycling at 900℃, the discontinuous coarsening was inclined to occur in the Al－segregation region in the alloy. And almost no spheroidized precipitates ofα2 were observed even after 1000 thermal cycles. After long－term thermal cycling at 1000℃, the massive γ grains were generated in the Al－segregation region. After 500 thermal cycles, the spherodized α2 precipitates were produced within γ grains which were found at colony boundaries. After 1000 thermal cycles, however, the large equiaxed γ grains containing different orientation of plate－shaped precipitates of theα2 phase were observed within the lamellar structure or at colony boundaries. After long－term thermal cycling at 1000℃, the plate－shaped or particle－shapedα2, which is coherent with the γ matrix, precipitates on the {111}γplane in the γ grain interior.
