Creep of Single Crystals of Nickel-Based Superalloys at Ultra-High Homologous Temperature
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Creep of Single Crystals of Nickel-Based Superalloys at Ultra-High Homologous Temperature ALEXANDER EPISHIN, BERNARD FEDELICH, GERT NOLZE, SINA SCHRIEVER, TITUS FELDMANN, MUHAMMAD FARZIK IJAZ, BERNARD VIGUIER, DOMINIQUE POQUILLON, YANN LE BOUAR, ANTOINE RUFFINI, and ALPHONSE FINEL The creep behavior of single crystals of the nickel-based superalloy CMSX-4 was investigated at 1288 C, which is the temperature of the hot isostatic pressing treatment applied to this superalloy in the industry. It was found that at this super-solvus temperature, where no c¢-strengthening occurs, the superalloy is very soft and rapidly deforms under stresses between 4 and 16 MPa. The creep resistance was found to be very anisotropic, e.g., the creep rate of [001] crystals was about 11 times higher than that of a [111] crystal. The specimens of different orientations also showed a very different necking behavior. The reduction of the cross-sectional area w of [001] crystals reached nearly 100 pct, while for a [111] crystal w = 62 pct. The EBSD analysis of deformed specimens showed that despite such a large local strain the [001] crystals did not recrystallize, while a less deformed [111] crystal totally recrystallized within the necking zone. The recrystallization degree was found to be correlated with deformation behavior as well as with dwell time at high temperature. From the analysis of the obtained results (creep anisotropy, stress dependence of the creep rate, traces of shear deformation, and TEM observations), it was concluded that the main strain contribution resulted from h011i{111} octahedral slip. https://doi.org/10.1007/s11661-018-4729-6 The Minerals, Metals & Materials Society and ASM International 2018
I.
INTRODUCTION
SINGLE-CRYSTAL nickel-based superalloys are used as blade materials for gas turbine aircraft engines and land-based gas turbines of power plants. These superalloys contain no large angle boundaries, which excludes intergranular oxidation and rupture. Nevertheless, the industrial technology of manufacturing of single-crystal blades cannot avoid the formation of micropores,[1] which significantly deteriorate the fatigue strength. Therefore, the advanced blade producers remove this structural defect by hot isostatic pressing (HIP), see e.g., Reference 2. The blades are usually
ALEXANDER EPISHIN is with the Technical University of Berlin, Berlin, Germany. Contact e-mail: [email protected] BERNARD FEDELICH, GERT NOLZE, SINA SCHRIEVER, and TITUS FELDMANN are with the Federal Institute for Materials Research and Testing (BAM), Berlin, Germany. MUHAMMAD FARZIK IJAZ, BERNARD VIGUIER, and DOMINIQUE POQUILLON are with the CIRIMAT/ University of Toulouse, Toulouse, France. YANN LE BOUAR, ANTOINE RUFFINI, and ALPHONSE FINEL are with the Laboratoire d’Etude des Microstructures, CNRS/ONERA (LEM), Chaˆtillon, France. Manuscript submitted March 14, 2018.
METALLURGICAL AND MATERIALS TRANSACTIONS A
HIPed at temperatures between c¢-solvus and solidus where superalloy has no strengthening c¢-phase and therefore is very
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