优质GH4738合金小变形条件下的组织演化

Microstructural Evolution of High-Quality GH4738 Alloy Under Small Deformation Conditions

摘要:

以优质GH4738合金作为研究对象，分析了不同小变形条件下，初始晶粒尺寸、热变形参数对该合金流变特性的影响，并采用光学显微镜、电子背散射衍射、透射电镜分析了优质GH4738合金热变形态及亚固溶处理态显微组织变化及软化机理。结果表明，在较低变形温度下流变应力与初始晶粒尺寸有着一定正相关性，随着变形温度的升高，初始晶粒尺寸的变化对流变应力影响变小；GH4738合金的动态再结晶体积分数对初始晶粒尺寸具有强烈的依赖性，变形温度的提高和工程应变量的增加均可以促进动态再结晶的发生。GH4738合金动态再结晶以晶界弓弯形核非连续动态再结晶机制为主，同时在动态再结晶及晶粒长大过程中，晶界处由于原子迁移发生小面化，产生类直角型台阶状的晶界。亚固溶处理过程中合金内部发生了静态再结晶，而且尚未完全回溶的强化相γ′促进再结晶形核，使得晶粒组织明显细化。

Abstract:

The effects of initial grain size and hot deformation parameters on hot deformation characteristics of high-quality GH4738 alloy under different small deformation conditions were analyzed. The microstructure evolution and softening mechanisms during hot working process and sub-solid solution treatment process were investigated by OM, EBSD and TEM analyses. The results indicate that the flow stress is increased with the increase in initial grain size, especially under the lower hot working temperature, and the increment is decreased with the increase in deformation temperature. The volume fraction of dynamic recrystallization in GH4738 alloy has a strong dependence on the initial grain size. Increasing the hot deformation temperature and engineering strain can promote the process of dynamic recrystallization of this alloy. The dynamic recrystallization mechanisms of GH4738 alloy are mainly based on the discontinuous dynamic recrystallization mechanism of nucleation of grain boundary bulging. In the meantime, during the process of dynamic recrystallization and grain growth, the grain boundary undergoes small planarization due to atomic migration, resulting in a quasi-right angle staged grain boundary. The static recrystallization occurs during the sub-solid solution treatment process, and the grains are refined to a great extent due to the incomplete re-dissolution strengthening γ' phase, which can promote the nucleation of static recrystallization.