A Nanocrystalline Ni₂(Cr,Mo) Intermetallic with Potentially Useful Combination of Properties for Gas Turbine Seal Ring Applications

Seal rings are installed for each turbine stage in gas turbine engines to minimize the loss in gas pressure and maintain engine efficiency. During service, seal rings become susceptible to failure by thermal fatigue as demonstrated by a case study. Therefore, a lower coefficient of thermal expansion is among the most important requirements for these applications. We show that long-range ordering in a Ni-Cr-Mo alloy can be used to synthesize a nanocrystalline intermetallic compound combining high strength, high ductility, low coefficient of thermal expansion, and an adequate oxidation resistance up to at least 700 °C. Twinning rather than slip is found to be the predominant deformation mechanism of the intermetallic compound, which is correlated with the crystallography of the disorder-to-order transformation and microstructure evolution. This could explain the enhanced plasticity of the intermetallic compound. The combination of enhanced plasticity, low-thermal expansion, and nano-sized crystals is expected to improve the resistance to thermal fatigue failure.