Authors: S L Semiatin P N Fagin R L Goetz D U Furrer R E Dutton
Publish Date: 2015/07/08
Volume: 46, Issue: 9, Pages: 3943-3959
Abstract
The plasticflow behavior which controls the formation of bulk residual stresses during final heat treatment of powdermetallurgy PM nickelbase superalloys was quantified using conventional isothermal stressrelaxation SR tests and a novel approach which simulates concurrent temperature and strain transients during cooling following solution treatment The concurrent cooling/straining test involves characterization of the thermal compliance of the test sample In turn this information is used to program the ramdisplacementvstime profile to impose a constant plastic strain rate during cooling To demonstrate the efficacy of the new approach SR tests in both tension and compression and concurrent cooling/tensionstraining experiments were performed on two PM superalloys LSHR and IN100 The isothermal SR experiments were conducted at a series of temperatures between 1144 K and 1436 K 871 °C and 1163 °C on samples that had been supersolvus solution treated and cooled slowly or rapidly to produce starting microstructures comprising coarse gamma grains and coarse or fine secondary gammaprime precipitates respectively The concurrent cooling/straining tests comprised supersolvus solution treatment and various combinations of subsequent cooling rate and plastic strain rate Comparison of flowstress data from the SR and concurrent cooling/straining tests showed some similarities and some differences which were explained in the context of the size of the gammaprime precipitates and the evolution of dislocation substructure The magnitude of the effect of concurrent deformation during cooling on gammaprime precipitation was also quantified experimentally and theoreticallyThis work was conducted as part of the inhouse research of the Metals Branch of the Air Force Research Laboratory’s Materials and Manufacturing Directorate in support of the Laboratory’s Foundational Engineering Problem FEP on bulk residualstress development in superalloys The support and encouragement of the FEP Program Managers Drs TJ Turner and MJ Caton are gratefully acknowledged The authors also thank GA Sargent and TA Parthasarathy for technical discussions on stressrelaxation testing and the modeling of strength in nickelbase superalloys and WM Saurber and EF Gaussa in performing the metallography One of the authors PNF was supported under the auspices of contract FA865010D5226
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