等温条件下Ti-1300合金亚稳β相的分解动力学

Decomposition Kinetics of Metastable β Phase in Ti-1300 Alloy under Isothermal Conditions

摘要:

通过高精度膨胀法研究了固溶态Ti-1300合金在400～700℃等温条件下相变动力学。研究表明：固溶态Ti-1300合金中亚稳β相的分解动力学可用Johnson-Mehl-Avrami(JMA)方程表征,并获得400～700℃温度范围内JMA方程的特征参数K和n,一定程度上反映了合金中亚稳β相的分解机制。当Ti-1300合金在400～420℃时效时,亚稳β相的分解方式主要为β_m→β′+β→α+β；当合金在500 ～700℃时效时,亚稳β相的分解方式主要为β_m→α+β；同时在等温条件下,时效初期α相的形核率较快,且含量迅速增加,后期达到一定量后保持稳定。根据计算和试验结果,得到了Ti-1300合金在500 ～700℃等温条件下亚稳β相的分解的TTT曲线,鼻尖温度约为600℃。

Abstract:

Phase transformation kinetics of Ti-1300 alloy after solution treatment were investigated under isothermal conditions in the temperature range of 400 to 700℃ by using dilatometric method. The decomposition kinetic equation of metastable β phase in the alloy was constructed under isothermal conditions by analyzing the experimental data in the theoretical frame of the Johnson-Mehl-Avrami theory. The different values of k and n parameters were obtained in the temperature range of 400 to 420℃ and 500 to 700℃, indicating that the mechanism of the phase transformation was different in different temperature ranges. The decomposition mechanism of metastable β phase is β_m→β′+β→α+β at the temperature of 400 to 420℃, whereas the decomposition mechanism of metastable β phase is βm→α+β at the temperature of 500 to 700℃. When the metastable β phase of Ti-1300 alloy was annealed isothermally at a given temperature, the amount of α phase increased firstly, and then reached a stable value with increasing the holding time. Based on calculation and experimental results, time-temperature-transformation diagrams (TTT diagram) of Ti-1300 alloys were plotted for the metastable β phase decomposition under isothermal conditions from 500 to 700℃. And the nose temperature of the TTT diagram of the alloy is around 600℃ for the Ti-1300 alloys.