2022 Fiscal Year Annual Research Report
Quantitative evaluation of the effect of process-induced defects on the fatigue limit of additively manufactured Ni-based superalloy in a hydrogen environment
| Project/Area Number |
22J12181
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| Research Institution | Kyushu University |
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Principal Investigator |
PARK SUNGCHEOL 九州大学, 工学府, 特別研究員(DC2)
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| Project Period (FY) |
2022-04-22 – 2023-03-31
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| Keywords | Additive manufacturing / Ni-based superalloy 718 / Fatigue limit / Small crack / Fatigue threshold |
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| Outline of Annual Research Achievements |
During this year, I have examined the fatigue limit of an additively-manufactured, Ni-based superalloy 718 in terms of the small, fatigue-crack growth-threshold, using samples with various small defects and microstructures. Based on the macro- and microscopic analyses, the determining mechanism of the fatigue limit, the effects of small defects and the factors impacting fatigue resistance were all thoroughly explored. The principal conclusions are summarized as follows:
1) Fatigue tests revealed that small-crack behavior was governed by maximum shear stress under both cyclic torsional loading and push-pull loading. This implied that the fatigue limit of all the samples was the threshold condition of a shear-mode, small fatigue-crack propagation, similar to the findings related to wrought materials.
2) In each case, the shear-mode, small fatigue-crack growth-threshold was estimated to quantify the effects of small defects. As a result, the relationship between the fatigue threshold and defect size was acquired, showing not only a crack-size dependence consistent with the results of wrought materials, but also a substantially low fatigue resistance of additively-manufactured materials.
3) Through the comprehensive examination of the effects of potential determining factors on small fatigue crack-growth resistance, it was concluded that the twist angle between two favorable slip planes in neighboring grains was the most influential factor in the inferior fatigue threshold of the additively-manufactured material.
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| Research Progress Status |
令和4年度が最終年度であるため、記入しない。
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| Strategy for Future Research Activity |
令和4年度が最終年度であるため、記入しない。
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