Study of phase decomposition and coarsening of γ′ precipitates in Ni-12at.% Ti alloy

The early stages of phase decomposition, morphological evolution of precipitates, coarsening kinetics of γ′ precipitates and micro-hardness in Ni-12at.% Ti alloy are studied by transmission electron microscopy (TEM) and Vickers hardness tests (VHN). Disk-shaped specimens are solution treated at 1473K (1200°C) and aged at 823, 923 and 1023K (550, 650 and 750°C) during several periods of time. TEM results show that a conditional spinodal of order occurs at the beginning of the phase decomposition and exhibit the following decomposition sequence and morphological evolution of precipitates: αsss→γ″ irregular–cuboidal+γs→γ′ cuboidal–parallelepiped+γ→η plates+γ. In general during the coarsening of γ′ precipitates, the experimental coarsening kinetics do not fit well to the LSW or TIDC (n=2.281) theoretical models, however the activation energies determined using the TIDC and LSW theories (262.846 and 283.6075kJmol−1, respectively) are consistent with previously reported values. The highest hardness obtained at 823, 923 and 1023K (550, 650 and 750°C) is associated with the presence of γ′ precipitates. •It was studied the conditional spinodal during early stages of phase decomposition.•It was obtained decomposition sequence and morphological evolution of precipitates.•It was experimentally evaluated the coarsening kinetics of γ′ precipitates.•The maximum hardness is associated with the γ′ precipitates.