High temperature creep of Ru-bearing Ni-base single crystal superalloys

Abstract

The response of high-refractory content Ni-base superalloys to high temperature creep deformation is primarily governed by microstructural changes. The present study investigates the creep behavior of advanced Ru containing single crystal superalloys. The main observation is that the improved stability provided by Ru additions hinders the formation of Topologically-Close-Packed (TCP) precipitates. Comparison of two nominally similar alloys with and without Ru reveals that the phase stability exhibited by the Ru containing alloy significantly improves the high temperature creep resistance. Ruptured and interrupted creep tests were carried out and studies related to high temperature creep mechanisms were performed. Microstructural investigations using scanning electron microscope (SEM) and transmission electron microscope (TEM) yielded information pertaining to the kinetics of rafting, TCP precipitate formation, γ′/γ lattice misfit, and compositional changes occurring at various stage of creep deformation. The primary mechanism associated with the improvement in high temperature creep resistance is attributed to the enhanced phase stability in Ru-bearing single crystal superalloys.