Coarsening process of coherent β′ precipitates in Fe-10 wt-%Ni-15 wt-%Al and Fe-10 wt-%Ni-15 wt-%Al-1 wt-%Cu alloys

The coarsening process of the NiAl ordered β′ precipitates was studied in the isothermally aged Fe-10 wt-%Ni-15 wt-%Al and Fe-10 wt-%Ni-15 wt-%Al-1 wt-%Cu alloys. The aging treatments at 750, 850 and 950 C caused the precipitation of the β′phase in a ferritic matrix. In general, the coarsening process of Cu containing alloy was slower with an activation energy of 248 kJ mol^-1 compared to 194 kJ mol^-1 for the other alloy. However, the coarsening kinetics for the former alloy was faster at 950 C. The precipitation hardening response was also better in the Cu containing alloy, with a slower overaging stage. The coarsening kinetics followed the behaviour predicted by the modified Lifshitz-Slyozov-Wagner theories for coarsening controlled by volume diffusion.