(燕山大學(xué) 機械工程學(xué)院，秦皇島 066004)
摘 要: 將TA15鈦合金在Gleeble-3800熱模擬試驗機上進行熱壓縮試驗，變形溫度為800~980 ℃。采用掃描電鏡(SEM)分析該合金的微觀組織演變規(guī)律，結(jié)合微觀組織定量結(jié)果及流變曲線對TA15鈦合金熱變形過程中熱力學(xué)進行評價。結(jié)果表明：TA15鈦合金在兩相區(qū)熱變形時會發(fā)生動態(tài)相變。動態(tài)相變使真實應(yīng)力-應(yīng)變曲線呈現(xiàn)明顯的流變軟化現(xiàn)象，造成屈服應(yīng)力顯著高于穩(wěn)態(tài)應(yīng)力。初生α相含量對變形溫度及應(yīng)變敏感。隨著變形溫度溫度的升高或應(yīng)變的增加，初生α相含量降低甚至完全消失，表明動態(tài)相變會造成TA15鈦合金相變點降低。TA15鈦合金動態(tài)相變是一種應(yīng)力驅(qū)動型相變，該合金發(fā)生動態(tài)相變的條件是驅(qū)動力克服能量勢壘。能量勢壘數(shù)值上等于最小臨界驅(qū)動力，且范圍約為70~742 J/mol，而最大驅(qū)動力范圍約為507~3306 J/mol。最大/最小臨界驅(qū)動力、能量勢壘均隨著變形溫度的升高而降低。
關(guān)鍵字: TA15鈦合金；流變軟化；動態(tài)相變；應(yīng)力驅(qū)動型；熱力學(xué)評價
（School of Mechanical Engineering, Yanshan University, Qinhuangdao 066004, China）
Abstract:The hot compression tests of TA15 titanium alloy were carried out on Gleeble-3800 thermomechanical simulator with a deformation temperature range of 800-980 ℃. The microstructure evolution of TA15 titanium alloy was analyzed by scanning electron microscopy (SEM). Combined with the quantitative data of microstructure and flow curve, the thermodynamics evaluation of TA15 titanium alloy during hot deformation was explained. The results show that dynamic transformation (DT) can be observed in TA15 titanium alloy during hot deformation below the β-transus temperature (Tβ), which can cause the true stress-strain curves to show apparently flow softening phenomenon leading to the yield stress significantly higher than the steady stress. The volume fraction of the primary α phase (fαp) is sensitive to deformation temperature and strain. With the increase of deformation temperature or strain, the fαp decreases or even disappears completely, indicating that the DT can cause the Tβ of TA15 titanium alloy to decline. The DT in TA15 titanium alloy is a stress-induced type, and its activation condition is that the driving force overcomes the energy barrier. The energy barrier value is numerically equal to the minimum critical driving force with 70-742 J/mol, and the range of the maximum driving force is 507-3306 J/mol. The maximum and minimum driving force and energy barrier decrease with the increase of deformation temperature.
Key words: TA15 titanium alloy; flow softening; dynamic transformation; stress-induced type; thermodynamics evaluation
