初始晶粒尺寸和强化相对GH4096高温合金热变形行为和再结晶的影响

Effects of Initial Grain Size and Strengthening Phase on Thermal Deformation and Recrystallization Behavior of GH4096 Superalloy

以镍基变形高温合金GH4096为研究对象,进行了不同组织状态下的热压缩实验,分析了该合金热变形流变行为特点,并采用OM、SEM、EBSD和TEM等手段研究了热压缩过程中初始晶粒尺寸(晶界面积和数量)和强化相对动态再结晶行为及组织演变的影响。结果表明:在1050~1120℃温度范围内,随着初始晶粒尺寸的减小,峰值流变应力降低,动态再结晶分数增加,实现完全动态再结晶所需热变形温度降低,发生动态再结晶的临界应变降低;在亚固溶温度下热变形时,动态再结晶晶粒尺寸与初始晶粒尺寸和变形量没有相关性;计算了与初始晶粒尺寸相关的热变形激活能,并建立了与热变形前的初始晶粒尺寸相关的热变形本构方程;研究了铸态组织中强化相γ’相形态对热变形行为的影响,在亚固溶温度下热变形时,随着强化相γ’相尺寸的增加,可一定程度降低热变形峰值流变应力,降低动态再结晶的临界应变,提高动态再结晶分数。分析讨论了GH4096合金不同组织状态下的主导动态软化机制。

GH4096 alloy were used for disks and shafts of advanced gas turbine engines owing to its excellent properties such as resistance to creep,fatigue,and corrosion as well as microstructure stability up to about 700oC.In this study,GH4096,a hard-to-deform disk superalloy,was processed through an advanced cast and wrought route to avoid the expensive power metallurgy(P/M) route.Many types of fullscale disk forgings possessing homogeneous fine-grained microstructures were successfully carried out,and the ultrasonic inspectability was comparative to that of the alloy produced by the P/M route.The effects of the initial grain size and strengthening phase on hot deformation behavior and dynamic recrystallization(DRX) were studied by OM,SEM,EBSD,and TEM under different deformation parameters.The results showed that as the initial grain size decreased within the temperature range of 1050-1120oC,the flow peak stresses decreased and the fractions of DRX increased.With an increase in the initial grain size,the thermal deformation temperature required for complete dynamic recrystallization decreased,and also the critical strain of dynamic recrystallization decreased.The initial grain size and the strain did not affect the recrystallized grain size when deformed at a sub-solvus temperature.The thermal deformation constitutive equations related to the initial grain sizes were established and the activation energies of thermal deformation related to the original grain sizes were calculated.The effect of γ' phase size on the thermal deformation behavior in as-cast microstructure was studied.In the sub-solvus temperature range,the thermal deformation resistance could be effectively reduced with the increase in the size of γ' phase,the critical strain of DRX was decreased,and the DRX fraction was also increased.The dynamic recrystallization mechanisms related to the γ' phase and initial grain size were also discussed.DRX nucleation takes place at the sub-grains near original grain boundaries for samples with larger initial grain size deformed at sub-solvus temperature.For samples with fine initial grain size,the interface slip of incoherent γ' phase is the significant dynamic softening mechanism during the sub-solvus temperature deformation.For ascast samples,the main dynamic softening mechanism is original grain boundary bowing out DRX nucleation and coarse second-phase-induced DRX nucleation.