铸造高温合金中氮的影响机理与控制

Effect mechanism and control of nitrogen in cast superalloys

总结中国科学院院金属研究所高温合金与金属间化合物课题组近年来开展的几种铸造高温合金中氮(N)的研究结果;讨论了铸造高温合金中N的控制方法。结果表明:无论镍基还是钴基铸造高温合金,N含量随Cr含量或返回次数和比例的增加而增大,过高的N含量降低合金的力学性能,并导致合金质量明显下降,但N的影响机理不同;对镍基铸造高温合金,N主要以极难分解的TiN颗粒团簇存在于合金熔体中,在凝固过程中作为核心促进TiC碳化物的析出与快速长大,块状碳化物阻塞枝晶间的通道,降低合金液的流动性和补缩性,导致合金组织中的显微疏松明显增加以及合金力学性能的降低;对钴基铸造高温合金,高N含量提高合金的初始凝固温度,使得合金枝晶组织粗大,枝晶间板条状M7C3共晶碳化物数量增多、尺寸增大,抑制周围基体中M23C6相的沉淀,导致共晶碳化物/基体界面更容易形成裂纹而降低合金力学性能。

The resent work in the Department of Superalloys and Itermetallic Composites,Institute of Metal Research,about the effect of nitrogen（N） on the microstructure and properties of cast superalloys was summarized.The control of N cast superalloys melting process was discussed.The results show that N content increases with the increase of Cr content in the virgin alloys,and the increment of recycle times or revert proportion in reverted alloys.Increasing N content considerably reduces the mechanical properties of both cast Ni-based superalloys and Co-based superalloys.In cast Ni-based superalloys,N reacts mainly with Ti to form TiN particles in the melt,which acts as profuse nucleus for subsequent carbides nucleation and growth at a higher temperature than in the normal solidification.These blocky carbides with large size can block the dendrite channels,and reduce the fluidity of the final liquid fraction and the permeability of the solidification structure.Consequently,increasing N content results in a greater degree of microporosity,which leads to a significant decrease in the mechanical properties of cast Ni-based superalloys.In Co-based superalloy,high N content will extend the solidification window during the solidification process,and then leads to the coarse carbide eutectic structure by increasing the quantity of the interdendritic Cr7C3 carbide eutectic,which restrains the M23C6 particles precipitates in the interdendritic regions.This microstructure is conducive to promote the initiation and propagation of the cracks and decrease the mechanical properties of cast Ni-based superalloys.