新型钴基高温合金长期时效组织演化研究

Microstructural Evolution During Long-Term Aging Treatment of Co-Based Superalloys

摘要:

新型钴基高温合金具有比镍基高温合金更高的γ′强化相稳定温度，其有望替代镍基高温合金应用于涡轮盘等服役环境苛刻的工程部件。为了解决钴基高温合金长期服役环境下的组织稳定性，对两种不同C含量的新型钴基高温合金进行900 ℃长期时效研究，系统解析了铸造态和固溶时效2种处理条件下γ′相和碳化物的尺寸、分布、成分和形貌演化规律。研究结果表明：两种钴基高温合金中γ′相的粗化均遵循LSW熟化理论，固溶时效态合金中γ′相的粗化速率高于铸态合金；含C钴基高温合金中的碳化物形貌和尺寸在长期时效过程中未见明显变化，当时效时间达到5000 h后，碳化物周围出现无析出区，并且固溶时效态合金中碳化物周围的无析出区面积更大，这主要是Ta、Ti等元素扩散降低了γ′相的热稳定性并发生溶解造成的。

Abstract:

The new Co-base superalloy has a higher γ′-strengthened phase stabilization temperature than the nickel-based superalloy， and is expected to replace the Ni-base superalloy in engineering components with harsh service environments such as turbine disks. It is of high engineering value to clarify the microstructure stability of cobalt-based superalloys in long-term service environments. Microstructural evolution during long term aging treatment at 900 ℃ were investigated in two types of Co-based superalloys with different carbon concentrations. The size and morphology of γ′ phase during aging treatment were characterized to illustrate the influence of pre-treatment. Microstructural characterization reveals that the coarsening rate of γ′ phase follows the LSW theory， suggesting the lattice misfitting between γ′ and γ determines the coarsening process. Coarsening rate of γ′ phase in the solution-aging treated sample is larger than in as-cast one. Carbides in the sample with carbon addition exhibit higher thermal stability. Free precipitation zone is formed around the carbides after aging treatment at 900 ℃ for 5000 h. Diffusion of Ta， Ti weakens the thermal stability of γ′ phase and promotes decomposition， resulting in the free precipitation zone around carbides.