The "necklace" structure of an advanced 4 th generation powder metallurgy (PM) superalloy after isothermal forging was investigated by means of scanning electron microscope, transmission electron microscope and electron back scattering diffraction technique. The formation mechanism and elimination method of the "necklace" structure were studied. The results show that after multiple isothermal forging, most region of the forging are fully recrystallized, and equiaxed fine-grained microstructures are obtained. Nevertheless, a typically incomplete recrystallization microstructure, namely the "necklace" structure, is formed nearing the upper and lower end faces of the forging. A great amount of fine recrystallized grains are distributed around the non-equiaxed deformed grains. The deformed grains contain a high density of low angle grain boundaries, so it means plenty of entangled dislocations exist. The samples containing "necklace" structure are annealed over the temperature range from 1080℃ to 1180℃. With the increasing temperature, both the recrystallization volume fraction and recrystallization grain size are increased gradually. The "necklace" structure of the alloy forging is basically eliminated after recrystallization annealing at 1150℃. Therefore, the uniform fine-grained disk can be obtained, which meet the requirements of dual microstructure heat treatment.%利用扫描电镜、透射电镜及电子背散射衍射技术研究新型第四代粉末高温合金等温锻造后的"项链"组织, 对其形成机理和消除方法进行了探讨.结果表明, 实验合金经过多火次等温锻造后, 锻坯大部分区域为再结晶后的等轴细晶组织;然而与模具接触的上下端面得到再结晶不完全的"项链"组织, 在非等轴变形晶粒周围分布着大量细小的再结晶晶粒, 变形晶粒内含有较高密度的小角度晶界, 缠结了大量位错.对存在"项链"组织的试样进行不同温度 (1080～1180℃) 的退火处理, 随着温度的升高, 再结晶体积分数和再结晶晶粒尺寸均不断增大.合金锻坯经过1150℃再结晶退火后, 可基本消除"项链"组织, 获得组织较均匀的细晶盘坯, 满足双组织热处理的要求.
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