TiAl合金中的γ→α析出转变行为

γ→α precipitation transformation in γ-TiAl alloy

研究了Ti 48Al和Ti 48Al 0.8B合金中的γ→α析出转变,分析了α析出相的生长形态、晶体学特征、生长动力学及α/γ相界面结构。结果显示α相从γ相中析出有两种方式:一种是从γ晶粒内沿{111}γ晶面以片状形貌析出,且α相与γ基体保持共格位向关系;另一种则是在γ晶界上通过不连续析出转变,以不规则的块状形貌析出,并向着晶界一侧与之无位向关系的γ晶粒内生长。添加0.8%(摩尔分数)B能显著降低γ晶粒内片状α析出相的形核率,并抑制α相生长。HREM分析表明:片状α相是在γ相的堆垛层错上形核,并通过"台阶凸起扭折"机制生长;α/γ相界面上复杂层错的存在及台阶形核率低是片状α相沿厚度方向生长缓慢的主要原因。

The mechanism of γ→α phase transformation in Ti48Al and Ti48Al0.8B alloys was studied. The morphological and crystallographic features, growth kinetics of α precipitate, and α/γ interphase boundary structure were analyzed. There are two ways of α phase precipitating from the γ matrix. The α plate, which is coherent with the γ matrix, precipitates on the {111}γ plane in the γ grain interior. Concurrently, the irregular α particle precipitates on the γ grain boundary through the discontinuous precipitation transformation. The addition of 0.8%(mole fraction)B into the Ti48Al alloy dramatically decreases the nucleation rate of α plate and impedes the growth of α phase. HREM analysis shows that the α plate nucleates on the stacking fault in the γ matrix and grows by the 'terraceledgekink' mechanism. The intricate stacking fault on the α/γ interphase boundary and the low nucleation rate result in very slow thickening of the α plate.