X-Ray Rocking Curve Measurements of Dislocation Density and Creep Strain Evolution in Gamma Prime-Strengthened Ni-Base Superalloys
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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.
Funding from the Services-AT, GE Global Research managed by Russell Irving and Vinod Kumar is gratefully acknowledged. Mallikarjun Karadge (GE Global Research, Niskayuna) and Stefan Haaga (Bruker) are thanked for their invaluable guidance during this reserch. B. K. Prasanna is thanked for performing the meticulous metallography work. The authors gratefully acknowledge the transmission electron microscopy work done by Amuthan Ramar.
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