On the nature of γ′ phase cutting and its effect on high temperature and low stress creep anisotropy of Ni-base single crystal superalloys

The creep anisotropy of the single crystal superalloy LEK 94 deformed in tension along [001] and [110] directions at 1293 K and 160 MPa was investigated. Elementary microstructural processes which are responsible for a higher increase in creep rates with strain during [110] as compared to [001] tensile loading were identified. [110] tensile creep is associated with a higher number of gamma' phase cutting events, where two dislocations with equal Burgers vectors of type (110) jointly shear the gamma' phase. The resulting (220)-type superdislocation can move by glide. In contrast, during [001] tensile loading, two dislocations with different (110)-type Burgers vectors must combine for gamma' phase cutting. The resulting (200)-type superdislocations can only move by a combination of glide and climb. The evolution of dislocation networks during creep determines the nature of the gamma' phase cutting events. The higher [110] creep rates at strains exceeding 2% result from a combination of a higher number of cutting events (density of mobile dislocations in gamma') and a higher superdislocation mobility ((220) glide) in the gamma' phase. 2014 Acta Materialia Inc. Published by Elsevier Ltd. All rights reserved.