Abstract
Abstract This research work studied the effect of aluminium, cobalt and nickel additions in superalloys grade GTD-111 and IN-738 on morphology of gamma prime particles and their lattice misfits after subjected to heat treatment and long-term cyclic exposure by using SEM and XRD. It was found that the particles became more cuboidal in shape after heat treatment in modified GTD-111 and IN-738 alloys. When adding 1 wt% aluminium and 6 wt% nickel, larger negative values of lattice misfit were found at −0.57 % and −0.28 %, respectively. However, 6 wt% cobalt addition reduced the negative value of the lattice misfit to −0.20 % in modified GTD-111 and small positive lattice misfit (+0.08 %) was found in modified IN-738. Also, modified GTD-111 alloy shows more spherical shape of the gamma prime precipitates than those in modified IN-738. After long-term cyclic exposure at 1173 K for 1440 ks, it was found that the particles become more spherical shape comparing to those of heat treated ones. The shape of particles in both modified alloys with 1 wt% aluminium and 6 wt% nickel additions maintained more cuboidal compared to others. Furthermore, the effect of 6 wt% cobalt addition is more pronounced for modified IN-738 than that of modified GTD-111.
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