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

C.G. Garay-Reyesa,⁎, F. Hernández-Santiagob, N. Cayetano-Castroc, V.M. López-Hiratad, J. García-Rochaa, J.L. Hernández-Riverae, H.J. Dorantes-Rosalesd, J.J. Cruz-Riveraa
M A T E R I A L S C H A R A C T E R I Z A T I O N 8 3 ( 2 0 1 3 ) 3 5 - 4 1, 2013.


The early stages of phase decomposition, morphological evolution of precipitates, coarsening kinetics of γ′ precipitates andmicro-hardness in Ni-12 at.% Ti alloy are studied by transmission electron microscopy (TEM) and Vickers hardness tests (VHN). Disk-shaped specimens are solution treated at 1473 K (1200 �C) and aged at 823, 923 and 1023 K (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 LSWtheories (262.846 and 283.6075 kJ mol−1,respectively) are consistentwith previously reported values. The highest hardness obtained at 823, 923 and 1023 K (550, 650 and 750 �C) is associatedwith the presence of γ′precipitates.