Acceleration of grain boundary cracking in ni-base alloy 617 under creep-fatigue loading at 800°C

Kenta Ishihara, Yifan Luo, Hideo Miura

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

Abstract

In recent years, in order to solve the global warming issue, the operating temperature of advanced thermal power plants has attempted to improve thermal efficiency and reduce CO2emissions. Under the creep and creep-fatigue conditions at elevated temperature, however, the effective lifetime of heatresistant alloys such as Ni-base Alloy 617, which has high strength and good corrosion resistance at about 750°C, was found to decrease drastically. Main reason for this short lifetime was attributed to the change in the crack initiation and propagation paths from transgranular one to intergranular one. Therefore, it is important to understand and express the criteria for grain boundary cracking. In this study, electron back-scatter diffraction (EBSD) analysis was applied to the visualization of the degradation process of the quality of grain boundaries in the alloy. The change in the crystallinity of grains and grain boundaries were continuously monitored during creep and creep-fatigue tests. It was found that accumulation of vacancies and dislocations degraded the crystallinity of grain boundaries and thus, their strength. The accumulation occurred around the specific grain boundaries which consisted of grains with large difference of Schmid factor during creep test. On the other hand, it occurred around all grain boundaries under the creep-fatigue loading. Thus, the accumulation of defects was clearly accelerated under the creep-fatigue loading. The critical image quality (IQ) value of intergranular cracking was almost the same regardless of the loading mode. Once the IQ value of the damaged grain boundaries decreased to a critical value, intergranular cracking started to occur at the grain boundaries.

Original languageEnglish
Title of host publicationMechanics of Solids, Structures, and Fluids
PublisherAmerican Society of Mechanical Engineers (ASME)
ISBN (Electronic)9780791884607
DOIs
Publication statusPublished - 2020
EventASME 2020 International Mechanical Engineering Congress and Exposition, IMECE 2020 - Virtual, Online
Duration: 2020 Nov 162020 Nov 19

Publication series

NameASME International Mechanical Engineering Congress and Exposition, Proceedings (IMECE)
Volume12

Conference

ConferenceASME 2020 International Mechanical Engineering Congress and Exposition, IMECE 2020
CityVirtual, Online
Period20/11/1620/11/19

Keywords

  • Creep-fatigue damage
  • EBSD analysis
  • Intergranular cracking
  • Ni-based alloy 617

ASJC Scopus subject areas

  • Mechanical Engineering

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