Re对一种定向凝固镍基高温合金微观组织的影响

INFLUENCE OF Re ON MICROSTRUCTURES OF A DIRECTIONALLY SOLIDIFIED Ni-BASED SUPERALLOY

采用SEM,EPMA和TEM等技术对不含Re(0Re)和含2%Re(2Re)的定向柱晶高温合金铸态和热处理态组织进行了系统的研究.结果表明:Re促进了铸态共晶外围和晶界上m相的析出;合金热处理后,Re明显促进了MC碳化物周围和晶界上相的析出,0Re合金MC碳化物周围只有少量的M6C相析出,晶界上有细小的M23(C,B)6硼碳化物析出,而2Re合金MC碳化物周围和晶界上都有大量块状m相析出,m相的析出促进了g′包层的形成.0Re合金中B元素明显偏聚于晶界,而2Re合金中B元素分布相对比较均匀.并对热处理过程中m相的析出机制进行了深入分析.

Up to now, considerable effort has been expended in attempts to investigate the influences of Re on Ni-based single crystal superalloys. However, few study had elucidated the influences of Re on carbide, boride and grain boundary. Therefore, the influence of a 2%Re （mass fraction） addition on the as-cast and heat-treated microstructures of a Ni-based directionally solidified superalloy was investigated by comparison with Re-free alloy using SEM, EPMA and TEM. The results show that Re accelerates the precipitation of μ phase in the periphery of eutectic and at grain boundary for as-cast microstructure. After heat treatment, Re also accelerates the precipitation of phase in the vicinity of primary MC carbide and at grain boundary. For ORe alloy, there are small number of M6C carbide in the vicinity of primary MC carbide and M23（C, B）6 boro-carbide at grain boundary. For 2Re alloy, a large amount of blocky p phase enveloped by thick y＇-fllm is found in the vicinity of primary MC carbide and at grain boundary. Enrichment of B along the grain boundary is observed in ORe alloy. On the contrary, relatively uniform distribution of B is found in 2Re alloy. The precipitation mechanism of p phase during the process of heat treatment is also analyzed.