热处理工艺对定向凝固高温合金4777DS再结晶的影响

Effect of Heat Treatment Process on Recrystallization of Directional-Solidified Superalloy 4777DS

摘要:

采用SEM、EBSD研究了不同热处理工艺、不同合金状态以及去应力退火工艺对4777DS合金再结晶缺陷的影响。合金不同热处理温度下保温后观察再结晶的情况表明：合金发生再结晶的温度为1055 ℃，热处理温度高于γ′相溶解温度时，再结晶呈现等轴再结晶形貌，而低于γ′相溶解温度时则呈现胞状再结晶形貌。随着热处理时间的延长，大角度晶界占比减少，产生的退火孪晶有助于降低畸变能。对比不同合金初始状态发生再结晶的情况可以发现，铸态合金发生再结晶的倾向最大，结合工程实际，发现较短时间的退火可有效地降低合金再结晶的情况。

Abstract:

The effects of different heat treatment processes, alloy states, and stress relief annealing processes on recrystallization defects in 4777DS superalloy were studied using SEM and EBSD. SEM observation shows that the γ′ phase near the surface of the sandblasted sample undergoes deformation, changing from an initial butterfly shape to a long strip distribution on the alloy surface. The observation of recrystallization of the alloy after insulation at different heat treatment temperatures shows that the temperature at which recrystallization occurs is 1055 ℃. When the heat treatment temperature is higher than the dissolution temperature of the γ′ phase, recrystallization presents an equiaxed morphology, while when the heat treatment temperature is lower than the dissolution temperature of the γ′ phase, it presents a cellular recrystallization morphology. With the prolongation of heat treatment time, the proportion of large angle grain boundaries decreases, and the resulting annealing twins help to reduce distortion energy. A comparison of recrystallization behavior under different initial alloy states reveals that the as-cast alloy exhibits the highest tendency for recrystallization. In line with practical engineering requirements, a shorter annealing time can effectively reduce the recrystallization degree of alloys.