PST双相TiAl类单晶高温变形位错特征

DISLOCATION FEATURES IN POLYSYNTHETICALLY TWINNED TiAl CRYSTALS AFTER DEFORMATION AT HIGH TEMPERATURE

利用透射电子显微镜研究了ＰＳＴ双相ＴｉＡｌ晶体高温变形后的位错组态。发现微孪晶变形、１／２＜１１０］单位位错、＜０１１］超点阵位错、１／２＜１１２］超点阵位错均参与了变形。螺型＜０１１］超点阵位错可在｛１００｝面上分解，构成Ｋｅａｒ－Ｗｉｌｓｄｏｒｆ锁。４００℃，６００℃变形时由１／２＜１１２］位错分解形成的层错偶极子仍然存在，但数量减少。８５０℃变形时未发现层错偶极子，但这时１／２＜１１２］刃型可动位错数量增加。原位加热观察表明，层错偶极子在６５０℃时完全消失。本文讨论了这些位错特征对ＴｉＡｌ合金韧脆转变特征的影响。

The dislocation features in polysynthetically twinned (PST) TiAl crystal deformed at 400, 600 and 850℃ have been investgated by TEM. Screw <011] superdislocations turned to dissociate on {100} planes to form Kear-Wilsdorf locks. Faulted dipoles were found in specimens deformed below 600℃ , whereas no faulted dipole was found at 850℃.In-situ heating observations on the faulted dipoles formed during deformation at room temperature indicated that the faulted dipole disappeared at about 600℃. Based on these experimental results, the mechanism of brittle-to-ductile of TiAl alloy has been discussed.