Effects of Cr on NiAl (β′) Precipitation in Ferritic Fe-Ni-Al Alloys

NiAl (beta ')-strengthened ferritic alloys are promising candidates for high-temperature applications. They present a coherent precipitate-matrix interface and are usually alloyed with 10 wt pct Cr to improve corrosion resistance and provide solid solution strengthening. In this work, the effects of Cr content on the precipitation of beta ' in Fe-Ni-Al ferritic alloys are studied using dilatometric analysis during continuous heating and cooling. The dilatometric data are correlated with microstructural observations, X-ray diffraction, and thermodynamic calculations. Additionally, isothermally annealed diffusion couples are used for determining the beta ' phase stability during isothermal conditions. Results indicate that an increase in Cr shifts the dissolution of beta ' to higher temperatures and the Curie point to lower values. Furthermore, the coarsening rate of the beta ' phase increases with the concentration of Cr. The addition of Cr implies a tradeoff between beneficial aspects like increased corrosion resistance and extended beta ' stability range against the partial loss of coherency and a higher coarsening rate. The agreement between thermodynamic calculations and the experimental data provides a useful insight for further materials development.