2021 Fiscal Year Annual Research Report
Explication of the degradation mechanism of the strength of heat-resistant alloys under random loading at elevated temperatures and the establishment of the prediction method of their lifetime
| Project/Area Number |
21F50350
|
|---|
| Research Institution | Tohoku University |
|---|
Principal Investigator |
三浦 英生 東北大学, 工学研究科, 教授 (90361112)
|
|---|
| Co-Investigator(Kenkyū-buntansha) |
WANG RUNZI 東北大学, 工学(系)研究科(研究院), 外国人特別研究員
|
|---|
| Project Period (FY) |
2021-11-18 – 2023-03-31
|
| Keywords | Strength of Materials / Heat-resistant Alloy / Creep-fatigue Damage / EBSD Analysis / Intergranular cracking |
|---|
| Outline of Annual Research Achievements |
The degradation process of the crystallinity of the representative heat-resistant alloy, Ni-base superalloy (GH4169), under creep-fatigue loading at elevated temperatures was monitored continuously by using our original intermittent micro tensile test method with electron microscopy. Original small dumbbell-shape specimens were manufactured for both the observation of the degradation process under the distribution of the applied load and the direct observation of the change of the local crystallinity of the alloy in a scanning electron microscope. The degradation of the strength of grain boundaries under creep-fatigue loading was validated by using a micro tensile test in a scanning electron microscope. The fracture life of the material was predicted by applying the modified Arrhenius equation. It was found that the activation energy of the generation and growth of defects such as vacancies and dislocations drastically decreased at grain boundaries under creep-fatigue loading, and the effective strength of the damaged grain boundaries was found to become lower than that of nearby grains, and thus, the fracture process was changed from transgranular one to intergranular one. The research results were published in 4 journal papers and one of them received the best poster award from the International Symposium on Structural Integrity, held in Hangzhou, China in 2021. In addition, two papers of the published 4 papers were SCOPUS top10% papers and others were top15% papers.
|
| Current Status of Research Progress |
Current Status of Research Progress
1: Research has progressed more than it was originally planned.
Reason
The degradation process of the crystallinity and strength of the grain boundaries of the target material was successfully visualized quantitatively by using the proposed intermittent creep-fatigue loading and EBSD analysis of the proposed micro specimens. Three journal papers have been published through this collaborative research project, and one of the papers was received the best poster award from the International Symposium on Structural Integrity, held in Hangzhou, China in 2021.
|
| Strategy for Future Research Activity |
The degradation process of the crystallinity and strength of the target material will be analyzed more in detail from the view point of the growth of precipitates such as delta-phase at grain boundaries. Since the crack propagation path under creep-fatigue loading was found to change from transgranular to intergranular under the creep-fatigue loading at elevated temperature, this growth of the delta-phase should play an important role on this change and thus, the drastic decrease of the fracture life. The accumulation of dislocations and vacancies around the precipitates will be explicated by applying the modified Arrhenius equation, and the drastic decreases in the strength of grain boundaries will be analyzed by the accumulation of these atomic-scale defects around the precipitates.
|
