粗晶GH4720Li合金热变形行为与动态再结晶特点

为了模拟难变形镍基高温合金GH4720Li开坯锻造过程,采用Gleeble-3800热模拟试验机研究经均匀化处理的GH4720Li铸锭高温压缩变形时的力学流动行为,分析高温变形过程中微观组织演化规律。结果表明,GH4720Li合金在1100℃,0.1 s-1条件下应力水平达到250 MPa,且应力对热变形温度和应变速率敏感,动态再结晶是主要的软化机制。粗晶组织提高了合金动态再结晶临界变形温度和应变速率,如在变形量为60%,变形条件为1140℃,0.001 s-1和1180℃,0.001s-1才能发生完全动态再结晶。计算的粗晶GH4720Li合金热变形激活能Q=1171kJ/mol,较高的热变形激活能表明粗晶组织不利于热塑性变形和动态再结晶的发生。基于本研究,铸态GH4720Li合金开坯温度应高于1140℃,同时保证较低的应变速率,以确保动态再结晶的充分发生,实现枝晶组织破碎。

Deformation behavior and dynamic recrystallization characteristic of a coarse U720Li alloy

To study the fogging of GH4720 Li nickel-based superalloy sufficiently,the hot deformation of the homogenization heat treated GH4720 Li was carried out on Gleeble-3800 hot simulation experiment machine,and the microstructure evolution during high temperature deformation was also analyzed.Results show that the flow stress of GH4720 Li at 1100°C/0.1 s-1 is about 250 MPa and it is sensitive to the deformation temperature and strain rate.Dynamic recrystallization is the main softening mechanism.Coarse grain improves the critical deformation temperature and strain rate for dynamic recrystallization,and complete dynamic recrystallization is obtained at 11401180°C under strain rate of 0.001 s-1.The thermal deformation activation energy is calculated as Q=1171 kJ/mol,and the higher thermal deformation activation indicates that the coarse grain is detrimental to hot workability and dynamic recrystallization for GH4720 Li alloy.It is revealed that forging temperature for coarse GH4720 Li alloy is determined above 1140°C,and low strain rate is necessary to ensure the occurrence of dynamic recrystallization and dendrite broken.