GH625合金的动态再结晶行为研究

Dynamic Recrystallization Behavior of GH625 Superalloy during Hot Deformation

摘要:

采用Gleeble-3800热模拟试验机研究了GH625合金在变形温度为950~1150 ℃，应变速率为0.001~5 s-1条件下的热变形特性，并用OM和TEM分析了变形条件对微观结构的影响。结果表明：当应变量很小时，该合金没有发生再结晶，直到应变量达到0.1时才开始有再结晶晶粒析出。随着变形温度的升高，再结晶晶粒尺寸增大，位错密度降低；当温度较低时显微结构中可以观察到孪晶。当变形温度一定时，随应变速率的增大，再结晶的形核率增大且晶粒变小，位错密度变大；而当应变速率较低时，再结晶进行得比较充分，晶粒尺寸较大。根据实测的应力-应变曲线，获得了该合金发生动态再结晶的临界应变εc和峰值应变εp与Z参数之间的关系：εc=2.0×10-3·Z0.123 85，lnεp= –6.022 85+0.123 85lnZ。此外，还采用定量金相法计算出了合金的动态再结晶体积分数，并建立了该合金动态再结晶的动力学模型：Xd=1–exp[–0.5634(ε/εp–0.79)1.313]。

Abstract:

The deformation behavior of GH625 superalloy was studied by the isothermal compression test in the temperature range of 950~ 1150 °C and the strain rate range of 0.001~5 s-1 and the effect of deformation condition on the microstructure was also investigated by OM and TEM. Results show that the dynamic recrystallization do not occur as the strain is little while the recrystallized grains appear when ε=0.1. As the deformation temperature increases, the recrystallized grain size increases and the dislocation density decreases; when the deformation temperature is low, some twins are observed in the matrix. As the strain rate increases, the nucleation rate increases and the grain size decreases, while the dislocation density increases at a constant deformation temperature; while at the low strain rate, the degree of recrystallization is high, which lead to the increase of grain size. According to stress-strain curves, the peak strain, the critical strain and the steady strain are obtained, and the relationship between the logarithmic values of the critical strain for DRX initiation () and the logarithmic value of the Zener-Hollomon parameter (lnZ) could be established as follows: lnεp= –6.022 85+0.123 85lnZ, εc=2.0×10-3·Z0.123 85. On the basis of quantitative microstructure analysis, the recrystallized volume fraction is also established as Xd=1–exp[–0.5634(ε/εp–0.79)1.313].