(中南大學 粉末冶金國家重點實驗室，長沙 410083)
摘 要: 對鍛造態(tài)的粉末冶金Ti-45Al-7Nb-0.3W(摩爾分數(shù)，%)合金進行后續(xù)熱處理，研究熱處理時間和熱處理溫度對合金組織演變的影響，利用掃描電鏡及透射電鏡對合金顯微組織進行觀察。結果表明：在1230~1260 ℃溫度區(qū)間熱處理可消除鍛造態(tài)合金的少量β相。在該溫度區(qū)間進行等時熱處理時，隨著熱處理溫度的升高，α晶粒和γ晶粒迅速長大，γ相體積分數(shù)急劇減小，且α晶粒趨于等軸化。合金在1260 ℃進行等溫熱處理時，熱處理時間由0.5 h延長至6 h，α晶粒和γ晶粒迅速長大，γ相體積分數(shù)降低，繼續(xù)延長熱處理時間，顯微組織沒有明顯的變化。通過計算可知，1260 ℃下α晶粒尺寸的極限值約為0.54 Dγ /Vγ(Dγ為γ晶粒尺寸；Vγ為γ晶粒體積分數(shù))。
關鍵字: TiAl合金；熱處理；組織演變；晶粒長大
（State Key Laboratory of Powder Metallurgy, Central South University, Changsha 410083, China）
Abstract:Powder metallurgy Ti-45Al-7Nb-0.3W (mole fraction, %) alloy was canned-forged and then heat-treated. The effects of heat treatment time and temperature on the alloy microstructure evolution were studied. The microstructures of as-forged alloy and heat-treated alloy were investigated by scanning and transmission microscopy. The results demonstrate that a few β grains in as-forged alloy are eliminated during heat treatments in the temperature range of 1230-1260 ℃. Isochronal annealing experiments show that the α grain size and γ grain size rapidly increase with increasing the temperature, while the volume fraction of γ phase steeply decreases and α grains become equiaxial. Isothermal annealing experiments at 1260 ℃ for 0.5-6 h reveal a sharp increase of α grain size and γ grain size with time. Meantime, the volume fraction of γ phase decreases. The microstructure of alloy shows no significant change during prolonging the annealing time. By calculation, the extreme α grain size at 1260 ℃ is approximately 0.54 Dγ /Vγ (Dγ is short for γ grain size and Vγ is short or the volume fraction of γ phase).
Key words: titanium aluminide alloy; heat treatment; microstructure evolution; grain growth
