(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析出轉(zhuǎn)變， 分析了α析出相的生長(zhǎng)形態(tài)、 晶體學(xué)特征、 生長(zhǎng)動(dòng)力學(xué)及α/γ相界面結(jié)構(gòu)。 結(jié)果顯示α相從γ相中析出有兩種方式： 一種是從γ晶粒內(nèi)沿{111}γ晶面以片狀形貌析出， 且α相與γ基體保持共格位向關(guān)系；另一種則是在γ晶界上通過不連續(xù)析出轉(zhuǎn)變，以不規(guī)則的塊狀形貌析出， 并向著晶界一側(cè)與之無位向關(guān)系的γ晶粒內(nèi)生長(zhǎng)。 添加0.8%(摩爾分?jǐn)?shù))B能顯著降低γ晶粒內(nèi)片狀α析出相的形核率， 并抑制α相生長(zhǎng)。 HREM分析表明： 片狀α相是在γ相的堆垛層錯(cuò)上形核， 并通過“臺(tái)階-凸起-扭折”機(jī)制生長(zhǎng)；αγ相界面上復(fù)雜層錯(cuò)的存在及臺(tái)階形核率低是片狀α相沿厚度方向生長(zhǎng)緩慢的主要原因。
關(guān)鍵字: TiAl合金; 相變; 形核與生長(zhǎng); 晶體位向; 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
