Phase transformation kinetics of high Nb-TiAl alloy during isothermal treatments
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摘要: 采用原位热膨胀法较为系统地研究了高Nb-TiAl合金的等温相变动力学。结果表明：高Nb-TiAl合金α2→α等温相变过程中，其“鼻尖”温度为1170 ℃，此温度下α相的转变速度最快，且该相的形成呈“S”曲线。基于热膨胀曲线，获取了等温过程中相应的JMA等温相变动力学方程，基于JMA方程，通过对数拟合相转变分数-时间曲线，获取高Nb-TiAl合金等温相变动力学Avrami指数n和温度常数K，建立了高Nb-TiAl合金温度-时间-相转变的定量关系TTT曲线（Time-Temprature-Transformation）；并揭示了合金扩散控制的相变动力学机制。
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关键词:
- 高Nb-TiAl合金 /
- 原位热膨胀法 /
- 等温相变 /
- 动力学
Abstract: The isothermal phase transformation kinetics of α2→α at the temperature 1140−1200 ℃ in high Nb-TiAl alloy were systematically studied by in-situ thermal expansion method. The results show that during the α2→α isothermal phase transformation of high Nb-TiAl alloy, the “nose tip” temperature of α2→α phase transformation is 1170 ℃, and the formation of α phase presents an “S” curve. Based on the thermal expansion curve, the corresponding JMA isothermal phase transformation kinetics equation during the isothermal process was obtained. On the basis of the JMA equation, the Avrami exponent n and temperature constant K of isothermal phase transformation of high Nb-TiAl alloy were obtained by logarithmic fitting the fractional time curve of phase transformation. Based on the results of thermal expansion measurement, the time-temperature-transformation diagram (TTT diagram) was plotted for high Nb-TiAl alloy. The phase transformation kinetics mechanism of high Nb-TiAl alloy controlled by diffusion was revealed. -
图 1 DIL曲线在等温过程中随时间的变化曲线
Figure 1. Viriation of DIL curves with time during aging at different temperature
图 2 高Nb-TiAl合金不同温度的等温过程中相变动力学曲线
Figure 2. Phase transformation kinetics cuvers of high Nb-TiAl alloys at different aging temperature
图 3 高Nb-TiAl合金在不同温度下的
$\ln(\ln({1 / {(1 - f)}})){{ - }}\ln{{t}}$ 关系Figure 3. Plots of
$ \ln(\ln(1/(1-f))) $ against$\ln t$ for the aging treatment at temperature for high Nb-TiAl alloy
图 4 高Nb-TiAl合金计算等温相变动力学曲线
Figure 4. Calculated phase transformation kinetics of high Nb-TiAl alloy during aging treatment
图 5 高Nb-TiAl合金的TTT曲线
Figure 5. The time-temperature-transformation (TTT) curves of high Nb-TiAl alloy
表 1 高Nb-TiAl合金等温相变JMA方程中的Avrami方程中指数n值与k值
Table 1. The Avrami exponen n and k value of JMA parameters for high Nb-TiAl alloys during aging treatment
T/℃ n k 1140 1.52 5.53×10−8 1160 2.70 9.94×10−14 1170 2.45 2.08×10−12 1180 2.51 6.45×10−13 1200 2.82 3.05×10−14 
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