Abstract: Microstructure evolution behavior for 16Cr-4.5Al, a nickel based alloy used for seals, is studied by scanning electron microscope (SEM) observation and image analysis after exposure at 700 ℃ for 24 h, 96 h, 312 h, 960 h, 1 512 h, 2 904 h and at 750 ℃ for 16 h, 96 h, 196 h, 288 h, 528 h respectively. In addition,the size growth of carbide and γ′ phase is also calculated based on the diffusion dynamics theory.Experimental and computational results both show that,the size stability of M23C6 carbide at grain boundary is generally accepted for the investigated alloy at the tested temperatures.Using diffusion modeling software DICTRA and its mobility database,the size changes of M23C6 carbide at different temperatures could be calculated,which have a good approximation with experimental results. The calculated results also show that carbide grows faster with larger grain size or higher C content of alloy.However, the coarsening of γ′ phase is significant, which conforms to the Ostwald ripe formula, and the macro hardness decrease is obvious during its long term exposure at 700 ℃.

Key words: superalloys, sealing materials, microstructure, phase stability, dynamics, coarsening