ON THE FORMATION OF [010]-DISLOCATIONS IN THE GAMMA'-PHASE OF SUPERALLOY SINGLE-CRYSTALS DURING HIGH-TEMPERATURE LOW-STRESS CREEP

The cutting of gamma'-particles by dislocations during shear creep def ormation of CMSX 6 superalloy single crystals loaded on the macroscopi c crystallographic shear system [110]{111} at T = 1025 degrees C and t au = 85 MPa is analysed using transmission electron microscopy (TEM). The formation of a [010]-dislocation in the gamma'-phase was observed and investigated by means of stereo microscopy, line trace and g.b-ana lysis. Two gamma-matrix channel dislocations with different Burgers ve ctors (b) of type a(0)/2[110] jointly shear the gamma'-particle where they form a superdislocation with a total Burgers vector of a(0)[010]. The present paper provides microstructural evidence for this high tem perature cutting process. The results are discussed in relation to the evolution of the dislocation structure in the gamma-channels during p rimary creep. Peach-Koehler forces were calculated to explain the form ation of the [010]-dislocation. (C) 1997 Acta Metallurgica Inc.