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采用高精度差分膨胀仪DIL805A/D测试了BT25钛合金在不同加热速度下的线膨胀曲线,并获得了合金在相应加热速度下的β相变温度。为了验证膨胀法得到的BT25钛合金β相变温度的准确性,用金相显微镜和定量分析软件分析了β相变温度附近不同温度保温后冷却得到的金相组织中相的相对含量和组织演变规律。根据膨胀曲线分析了BT25合金在加热过程中,不同温度范围内的相变情况。最后,采用杠杆定律得到不同加热过程中BT25合金α→β相变时α相转变体积分数与温度之间的变化关系。研究结果表明:膨胀法能够准确测定不同加热速度下钛合金的α→β相变点;随着加热速度的增加,BT25钛合金α→β相变的起始温度和结束温度都升高,相变温度区间变窄,相变速率明显增大。相变速率峰值和出现峰值的温度随着加热速度的增加也增大;利用Kissinger方程计算得出了加热过程中BT25钛合金α→β相变激活能为953.15 k J·mol~(-1)。
The linear expansion curves of BT25 titanium alloy at different heating rates were tested by using DIL805A / D high precision differential dilatometer, and the β transformation temperature of the alloy at the corresponding heating rate was obtained. In order to verify the accuracy of β transformation temperature of BT25 titanium alloy obtained by the expansion method, the relative content and microstructure evolution of the phase in the microstructure of the microstructure after cooling at different temperatures around β transformation temperature were analyzed by metallographic microscope and quantitative analysis software law. According to the expansion curve, the phase transformation of BT25 alloy in different temperature range was analyzed. Finally, by using the law of leverage, the relationship between the volume fraction of α-phase transformation and temperature during the α → β phase transformation of BT25 alloy was obtained under different heating conditions. The results show that the expansion method can accurately measure the α → β transformation temperature of titanium alloy at different heating rates. The initial temperature and the end temperature of α → β phase transformation of BT25 titanium alloy increase with the increase of heating rate. Variable temperature range narrowing, phase transition rate increased significantly. The phase transition rate peak and peak temperature also increased with the increase of heating rate. The Kissinger equation was used to calculate the activation energy of α → β phase transition of BT25 titanium alloy was 953.15 kJ · mol ~ (-1) .