Ti-6Al-4V合金熔模鑄造過程中的固態相變微觀組織演變數值模擬

Ti-6Al-4V合金熔模鑄造過程中的固態相變微觀組織演變數值模擬NUMERICAL SIMULATION OF MICROSTRUCTURE EVOLUTION DURING THE SOLID PHASE TRANSFORMATION OF Ti-6Al-4V ALLOY IN INVESTMENT CASTING

熔模鑄造被廣泛應用于復雜薄壁鈦合金零件的生產，在此工藝中，鈦合金的β→α相變決定了最終的鑄態組織。然而現有的關于鈦合金固態相變微觀組織的研究多集中于熱處理或熱變形條件下微觀組織的演化，對鑄造過程中鈦合金固態相變微觀組織的演變鮮有研究。本文針對Ti-6Al-4V合金熔模鑄造固態相變過程中的微觀組織演變，對α層片的生長，采用了不同的模型分別計算層片邊緣和層片寬面的生長速度，模擬得到了多個α集束競爭生長的微觀組織。模擬結果表明，Ti-6Al-4V合金熔模鑄造固態相變過程中，α層片邊緣生長受應變能及雜質元素影響較小，而在寬面上應變能引起的過冷度以及雜質元素含量變化引起的過冷度變化之和占總過冷度的比例約為0.45；Ti-6Al-4V合金熔模鑄造固態相變焓變約為70kJ/kg，與JMatPro吻合較好。模擬得到的組織形態結果與金相組織吻合較好，模擬得到的生長速度也與實驗估測的速度相當，表明本文可以較好地應用于Ti-6Al-4V合金熔模鑄造固態相變微觀組織演變的模擬。

Investment casting is widely used in the production of complex thin-wall Titanium alloy components. The β→α phase transformation decides the final microstructure in this process. However most of present studies on the phase transformation of titanium alloy are about the microstructure evolution in forging or heat treatment process rather than casting process. This study was aiming at the solid phase transformation of Ti-6Al-4V alloy in investment casting. In this study, different models were applied to get the growth rate in the edge and the broad face of α plates. The growth competition of different colonies, which consisted of α plates of the same orientation, was simulated and the microstructure and temperature evolution were obtained. The comparison between the simulated microstructure and temperature evolution and experimental data indicated that strain energy and impurities occupied about 45% of total undercooling in the broad face of α plates and a much smaller portion in the edge. The comparison also showed that the enthalpy change of the solid phase transformation of titanium alloy should be about 70kJ/kg. The simulated and experimental morphology were the same and simulated growth rate was in good accordance with experiment inferred growth rate. This showed that this study was applicable to numerical simulation of the solid phase transformation of Ti-6Al-4V alloy in investment casting.

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