X-Ray Rocking Curve Measurements of Dislocation Density and Creep Strain Evolution in Gamma Prime-Strengthened Ni-Base Superalloys

A linear relationship between mobile dislocation density and creep strain has generally been assumed in various models of creep in Ni-base superalloys. No stress or temperature dependence is assumed in such relationships. The current study aims to verify this relationship by use of an X-ray rocking curve-based method on DS GTD111™, a directionally solidified (DS) nickel-base turbine blade alloy. A new measurement scheme tailored for such large-grained, DS alloys using simultaneous tilt–twist methodology is outlined. Multiple test sets of DS GTD111™, creep tested under varying boundary conditions, were measured using this technique. The resulting rocking curve full-width-half-maxima (square root of the dislocation density) were found to correlate to creep strain by a simple linear transfer function with no systematic dependence on stress or temperature. As a validation case, application of this transfer function is demonstrated for long-term test data.