镍基单晶高温合金的动态再结晶

摘要

The dynamic recrystallization behavior of single-crystal(SC) superalloy SRR99 at low strain rate was investigated by high-temperature creep testing. The results show that dynamic recrystallization may take place after the uncoated samples have been creep-tested in air at high temperature and low stress for a long time. Both the threshold temperature and strain for the dynamic recrystallization of SC superalloy SRR99 at low strain rate are lower than those for the static recrystallization. Dynamically recrystallized grains with the depth less than 15 µm are only located in the surfaceγ'-free layers, and the recrystallized grains are well-developed grains without columnarγ' precipitates within them. The dynamic recrystallization behavior of SC superalloy SRR99 at low strain rate is mainly related to high-temperature oxidation. Suitable protective coating can effectively prevent the dynamic recrystallization of SC superalloy components in service. In addition, the dynamic recrystallization behavior of SC superalloy SRR99 at high strain rate was also studied by high-temperature compression testing. At high strain rate, a higher temperature and larger strain are needed for the occurrence of dynamic recrystallization than at low strain rate, and the recrystallized grains have cellular structures with an amount of columnarγ' precipitates within them.%利用高温蠕变试验，研究 SRR99单晶高温合金在低应变速率下的动态再结晶行为。结果显示，在大气环境且无涂层保护的情况下，长时间高温低应力作用会使单晶合金发生动态再结晶，动态再结晶的温度和临界应变量均低于静态再结晶，再结晶晶粒均位于试样边缘的γ'相贫化层内，再结晶深度较浅，一般不超过15µm。在高温低应变速率下，再结晶以完整晶粒的形式发生，晶粒内无条状γ'相存在。单晶合金在高温低应变速率下的动态再结晶行为主要与高温氧化有关。在实际服役条件下，表面涂层可有效抑制动态再结晶的发生。此外，还利用高温压缩试验，研究了 SRR99单晶合金在高应变速率下的动态再结晶行为。在高应变速率下，单晶合金发生动态再结晶的温度和临界应变量均显著提高，再结晶以胞状组织的形式发生，晶胞内含有大量粗大的条状γ'相。