The role of alloying elements on gamma' phase growth kinetics in Ni-base alloys

This work concerns the kinetics of gamma' precipitation in experimental Ni-base alloys. The work was motivated by the need for the partial substitution of Cr for Al to prevent TCP phase formation while maintaining the corrosion resistance of the alloys. The composition of the alloys was characterized by low Cr content (15 wt.% instead of 20 wt.% in commercial wrought Ni-base superalloys), various Al contents, 1.5 wt.% of Ti and 5 wt.% of Mo. The alloys were solution-treated followed by aging for up to 1100h at 700 degrees C and 144h at 900 degrees C. The coarsening of gamma' particles was studied using SEM, EDS and TEM techniques. The results show that the coarsening follows the Lifshitz-Slyozov-Wagner (LSW) law. The kinetic constant, determined experimentally, depends on the lattice parameter mismatch between gamma and gamma' phases, which in turn reflects the effect of elastic strains on the coarsening.