变形参数对GH4742合金动态再结晶及γ′相的影响

 为了研究不同变形参数对锻态GH4742合金动态再结晶及γ′相的影响,利用单道次等温压缩试验获得了变形温度为1 050～1 150 ℃、变形量为30%～70%、变形速率为0.1 s-1时的真应力-真应变曲线,分析了不同变形参数下真应力-真应变曲线以及峰值应力的变化规律,同时采用SEM、EBSD对不同变形参数下动态再结晶过程中的亚结构以及γ′相进行了精细表征,定量计算了基体内的几何位错密度以及发生动态再结晶的比例,并测试了不同变形参数下基体的硬度。重点探讨了不同变形参数下动态再结晶的形核机制,深入分析了动态再结晶过程中亚结构以及γ′相的演变规律。结果表明,变形温度为1 080 ℃时,基体中存在大量未溶的一次γ′相,小角度晶界比例超过35%,基体发生动态再结晶比例小于35%,主要形核方式为连续动态再结晶。变形温度为1 110 ℃,一次γ′相尺寸减小并发生回溶,小角度晶界比例小于8%,基体发生动态再结晶比例超过75%,主要形核方式为不连续动态再结晶。随着变形量增加,一次γ′相尺寸增大、数量密度降低,小角度晶界比例显著下降,动态再结晶比例明显提高。低温变形时基体硬度随着变形量增加而显著增加,而高温变形时硬度先增加后逐渐趋于不变。GH4742合金变形温度为1 110 ℃时,变形量50%时已完成动态再结晶,组织为等轴的动态再结晶晶粒,基体硬度较低,为357HV,在此变形参数下加工具有良好的热成型性能。

Effect of deformation parameters on dynamic recrystallization and γ'-phase of GH4742 superalloy

In order to study the effects of deformation parameters on the dynamic recrystallization and γ′ phase of forged GH4742 superalloy,the true stress-true strain curves of forged GH4742 superalloy at deformation temperature of 1 050-1150 ℃ and the deformation ratio of 30%-70% under the strain rate of 0.1 s-1were obtained by single-pass isothermal compression experiments,the variation of true stress-true strain and peak stress under different deformation parameters was analyzed,and meanwhile the micro-substructure and γ′ phase were characterized during the dynamic recrystallization process under different deformation parameters by SEM and EBSD, the geometric dislocation density of the matrix and the proportion of dynamic recrystallization were quantitatively calculated,and the hardness of the matrix under different deformation parameters was measured. The nucleation mechanism of dynamic recrystallization under different deformation parameters was discussed,and the evolution of micro-substructure and γ′ phase was deeply analyzed during the dynamic recrystallization process. The results show that there were a large number of undissolved primary γ′ phase in the matrix at deformation temperature of 1 080 ℃,the proportion of low-angle grain boundaries(LAGs) exceeded 35%,and the proportion of dynamic recrystallization was less than 35%,and the nucleation mechanism was mainly continuous dynamic recrystallization; The size of the primary γ′ phase decreased,and then it re-dissolved progressively in the matrix at deformation temperature of 1 110 ℃,the proportion of LAGs was less than 8%,and the proportion of dynamic recrystallization was more than 75%,and the main nucleation mechanism was discontinuous dynamic recrystallization. With increasing deformation ratio,the size of primary γ′ phase increased and the number density of that decreased,the proportion of LAGs decreased significantly,and the proportion of dynamic recrystallization of the matrix increased. The hardness of the matrix increased significantly with the increase of the deformation ratio at the low deformation temperature,whereas the hardness increased first and then gradually tend to remain unchanged at the high deformation temperature. The dynamic recrystallization of GH4742 alloy had been completed at the deformation temperature of 1 110 ℃ and the deformation ratio of 50%,the microstructure was equiaxed dynamic recrystallized grains,and the matrix hardness was 357HV,which had a good hot forming performance.