(北京航空材料研究院， 北京 100095)
摘 要: 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；αγ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。
关键字: TiAl合金; 相变; 形核与生长; 晶体位向; 相界面
in γ-TiAl alloy
（Beijing Institute of Aeronautical Materials, Beijing 100095, China）
Abstract: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 αγ 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 αγ interphase boundary and the low nucleation rate result in very slow thickening of the α plate.
Key words: TiAl alloy; phase transformation; nucleation and growth; orientation relationship; phase boundary
