Creep behavior and a deformation mechanism based creep rate model under high temperature and low stress condition for single crystal superalloy DD5

Abstract

This work reports the investigation on creep behavior under high temperature and low stress condition for single crystal superalloy DD5 and the subsequent establishment of a deformation mechanism based creep rate model. The γ/γ′ microstructure evolution and the precipitate-dislocation interaction mode were investigated systematically during creep test at 1100 °C and 120 MPa, for a better understanding of underlying creep deformation characteristics. The γ/γ′ microstructure becomes rafted and topological inverted eventually as creep deformation continues. The formation of dense interfacial dislocation network that impedes dislocations from cutting into γ′ precipitates is assumed to be one of the main strengthening mechanisms during creep. The climbing over rafted γ′ precipitates is seen as a recovery/softening process which annihilates dislocations, receding the strengthening effect of interfacial dislocation network. The cutting through rafted γ′ precipitates is proposed to account for the acceleration of creep, a strong dependence of creep properties on rafting (the effect of widening horizontal γ channel on the degraded back stress of cutting through rafted γ′ precipitates) then arises. The established model involving these characteristics was found to predict the creep behavior (below 1% creep strain) under different temperatures and stresses for single crystal superalloy DD5 accurately. Several microstructure characteristics and physical properties emerge from the model, which is promising for alloy design and compositional optimization.