Creep-damage-induced deterioration of the strength of ni-base superalloy due to the change of its microstructure

Hayato Sakamoto, Ken Suzuki, Hideo Miura

Research output: Chapter in Book/Report/Conference proceedingConference contribution

4 Citations (Scopus)

Abstract

Ni-base superalloys are widely used for various power plants and jet engines. Since the operating temperature of thermal plants and equipment has been increasing to improve their thermal efficiency for decreasing the emission of carbon-dioxide, the initially designed microstructure was found to change gradually during their operation. Since this change of microstructure should deteriorate the strength of the materials, sudden unexpected fracture should occur during the operation of the plants and equipment. Therefore, it is very important to clarify the dominant factor of the change of the microstructure and the relationship between the microstructure and its strength for assuring the stable and reliable operation of the plants and equipment. In this study, the change of the strength of a grain and a grain boundary of Ni-base superalloys caused by the change of their microstructure was measured by using a micro tensile test system in a scanning ion microscope. A creep test was applied to bulk alloys at elevated temperatures and a small test sample was cut from the bulk alloy with different microstructure caused by creep damage by using focused ion beams. The test sample was fixed to a silicon beam and a micro probe, respectively, by tungsten deposition. Finally, the test sample was thinned to 1µm and the sample was stretched to fracture at room temperature. The change of the order of atom arrangement of the sample was evaluated by applying electron back-scatter diffraction (EBSD) analysis quantitatively. In this study, the quality of grains in Ni-base superalloys was analyzed by using image quality (IQ) value calculated by using Hough transform of the observed Kikuchi pattern. It was found that the order of atom arrangement was deteriorated monotonically during the creep tests and this deterioration corresponded to the change of the microstructure clearly. Both the yield strength and the ultimate tensile strength of a grain in the alloys decreased drastically with the change of the microstructure, in other words, the IQ value of the grains. There was a clear relationship between the IQ value of a grain and its strength. Therefore, this IQ value is effective for evaluating the crystallinity of the alloys and the remained strength of the damaged alloys. The change of the microstructure was dominated by the strain-induced anisotropic accelerated diffusion of component elements of the alloys and the activation energy of the diffusion was determined quantitatively as a function of temperature and the applied stress.

Original languageEnglish
Title of host publicationMechanics of Solids, Structures and Fluids; NDE, Structural Health Monitoring and Prognosis
PublisherAmerican Society of Mechanical Engineers (ASME)
ISBN (Electronic)9780791858448
DOIs
Publication statusPublished - 2017 Jan 1
EventASME 2017 International Mechanical Engineering Congress and Exposition, IMECE 2017 - Tampa, United States
Duration: 2017 Nov 32017 Nov 9

Publication series

NameASME International Mechanical Engineering Congress and Exposition, Proceedings (IMECE)
Volume9

Other

OtherASME 2017 International Mechanical Engineering Congress and Exposition, IMECE 2017
CountryUnited States
CityTampa
Period17/11/317/11/9

ASJC Scopus subject areas

  • Mechanical Engineering

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    Sakamoto, H., Suzuki, K., & Miura, H. (2017). Creep-damage-induced deterioration of the strength of ni-base superalloy due to the change of its microstructure. In Mechanics of Solids, Structures and Fluids; NDE, Structural Health Monitoring and Prognosis (ASME International Mechanical Engineering Congress and Exposition, Proceedings (IMECE); Vol. 9). American Society of Mechanical Engineers (ASME). https://doi.org/10.1115/IMECE2017-70317