GH742合金热变形行为与微观组织演化

HOT DEFORMATION BEHAVIOR AND MICRO-STRUCTURE EVOLUTION OF SUPERALLOY GH742

在MTS热模拟实验机上采用等温压缩实验的方法研究了GH742合金热塑性变形行为,获得了合金在温度为950- 1150℃、应变速率为0.001-1s-1的热加工变形条件范围内的流变应力数据,并对合金变形过程中的组织演变过程进行了分析.结果表明,当合金在1075℃以上的单相区内变形时具有低的流变应力,合金的表观激活能接近晶界扩散激活能,变形行为受再结晶晶界迁移过程的控制,易于获得充分动态再结晶组织.在两相区内,GH742合金具有高的表观激活能,随着变形温度的下降和应变速率的增大,流变应力大幅度升高.同时动态再结晶过程受到抑制.在单相区与两相区交界温度范围内.流变应力出现台阶式突变,同时表观激活能大幅度升高,由于应变诱导析出γ′相抑制了再结晶晶界的迁移,再结晶晶粒直径随变形量的增加而大幅度减小,从而使微观组织得到有效的细化.

Hot deformation behavior of superalloy GH742 was studied by isothermal compression test conducted on MTS machine. Flow stress data at various temperatures from 950℃ to 1150℃ and strain rates from 0.001 s^-1 to 1 s^-1 were obtained, microstructure evolution during deformation under the above conditions was also investigated. The results show that when deformation was performed at single phase region above 1075℃, rather low flow stress is exhibited, the apparent activation energy approachs the activation energy of grain boundary diffusion, the deformation mechanism is controlled by grain growth rate and the fully recrystallized structures can be achieved. In two phase region, GH742 alloy presents considerably high activation energy, with decreasing temperature and increasing strain rate the flow stress increases swiftly, while the dynamic recrystallization was strongly prohibited. At transition temperature between single and two phase regions, a discontinuous change in flow stress was observed, and the apparent activation energy sharply increased, strain induced dynamically precipitated γ＇ phase inhibits the migration of grain boundaries, the diameter of the recrystallized grain is drastically reduced with increase of plastic strain, and the microstructure was effectively refined