700℃超超临界机组用Alloy 617 mod时效析出相

Aging Precipitates of Alloy 617 mod Used for 700 ℃ Ultra Supercritical Unit

研究了Alloy617mod在750℃下时效3000h过程的析出相种类及其对室温硬度和冲击性能的影响。Alloy617mod时效后析出M23C6碳化物和γ′相。随时效时间延长，晶内、晶界析出物数量增多，晶界碳化物尺寸和分布无明显变化。经300h时效后，M23C6和γ′相产生析出强化，提高了合金硬度。晶界碳化物导致界面结合强度降低，晶界成为裂纹的发源地，引起冲击吸收能量降低。时效过程γ′相与基体相保持共格关系，产生共格应力，有利于硬度提高；同时γ′相析出强化使晶界附近难以协调塑性变形，易导致开裂，也引起冲击吸收能量降低。时效300-3000h过程的时效态Alloy617mod硬度和冲击吸收能量分别为207-214HB和75～83J，具有良好的稳定性。

Precipitates of Alloy 617 mod and their effect on the room temperature hardness and impact property were investigated during 3 000 h aging at 750 ℃. The precipitates of the aged alloy were M23C6 carbide and γ′. With increasing aging time, the number of intra-and inter-granular precipitates increased. The size and distribution of grain boundary carbides took no obvious change during aging. After aging for 300 h, precipitation strengthening of M23C6 and γ′ phase is conducive to an enhanced hardness of the aged alloy. The bonding strength at interfaces is weakened by M23C6 at grain boundaries induced the initiation of cracks at that area, leading to a decrease of the impact absorbed energy. The coherency between γ′ phase and the matrix is maintained during aging and resulted in a coherent stress for the aged alloys, thus giving rise to an enhanced hardness. The precipitation strengthening of γ′ phase of the aged alloys limits plastic deformation to the area nearby grain boundaries and results in the occurrence of crack along grain boundaries, giving rise to a decrease of impact absorbed energy. The hardness and impact absorbed energy of the aged alloys is rather stable within the dwelling time from 300 h to 3 000 h and was in the range of 207-214 HB and 75-83 J, respectively.