镍基单晶高温合金的表面再结晶行为

摘要

利用喷丸预变形,研究了热处理温度对单晶高温合金表面再结晶行为的影响以及固溶温度条件下再结晶组织的演变过程.结果表明,随着热处理温度的升高,再结晶层厚度不断增加；在1200℃C以下时,再结晶层厚度随着温度的升高而缓慢增加,而当温度高于1200℃C时,再结晶层厚度随着温度的升高而迅速增加；当热处理温度低于γ′相完全固溶温度时,再结晶以不连续的胞状组织的形式出现,而当热处理温度高于γ′相完全固溶温度时,再结晶以完整晶粒的形式出现；再结晶晶粒首先在喷丸表面的枝晶干区域形核,然后沿着枝晶干向内生长,但随着枝晶间粗大γ′相和γ/γ′共晶相的溶解,再结晶晶界穿过枝晶间区域而继续向内部迁移,最后形成厚度比较均匀的再结晶层;铸态γ′相的溶解是影响单晶高温合金再结晶行为的关键因素.%As-cast single crystal (SC) superalloy samples were shot peened and then annealed at different temperatures to investigate the effect of annealing temperature on the surface recrystallization behavior of the SC superalloy.The results show that the depth of recrystallized layers increases with the increase of annealing temperature.Below 1200 ℃,the recrystallization depth climbs slowly with temperature rising.Above 1200 ℃,the recrystallization depth increases sharply with the rise of temperature.The morphology of recrystallized grains is significantly affected by annealing temperature.Below the γ′ solvus,cellular recrystallization may be observed.Above the γ′ solvus,recrystallization occurs through the growth of well developed recrystallized grains.In addition,the microstructure evolution of recrystallized grains at the homogenization annealing temperature was studied.It is found that recrystallized grains first nucleate in the dendritic core areas on the shot-peened surface and then grow inwards along the dendritic core areas.With the dissolution of the coarse γ′ precipitates and γ/γ′ eutectics in the interdendritic areas,the recrystallized grain boundaries move through the interdendritic areas.Finally,the fully developed grains nearly have a uniform depth.The dissolution of primary γ′ precipitates is a critical factor influencing the recrystallization behavior of SC superalloys.