2022 Fiscal Year Research-status Report
Enhancement of strength-ductility trade-off by microstructure control of C-doped FeNiCoCr HEA.
| Project/Area Number |
22K20478
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| Research Institution | Yokohama National University |
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Principal Investigator |
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| Project Period (FY) |
2022-08-31 – 2024-03-31
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| Keywords | High entropy alloys / Microstructure / Neutron diffraction / Heat treatment / Plastic deformation / Mechanical properties |
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| Outline of Annual Research Achievements |
The 1%C-doped CoCrFeNi HEA performed high deformability by larger 60% thickness reduction of cold-rolling without macroscopic crack. As-rolled sample obtained high dislocation density resulting in the microhardness of 398 HV. The microstructure evolution of as-rolled samples was studied during isochronal annealing (1 hour) at 978, 1078 and 1178 K in terms of grain morphology, dislocation density and carbide precipitation. The solute drag effect and carbide precipitations due to carbon addition delayed the recrystallization process. In the fully recrystallized microstructure after 1178 K heat-treatment, the average grain size is about 4 microns and the microhardness is about 228 HV. The fine recrystallized grains were resulted by large dislocation density of as-rolled sample.
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| Current Status of Research Progress |
Current Status of Research Progress
2: Research has progressed on the whole more than it was originally planned.
Reason
After obtaining the relationship between microstructure and annealing temperature, the larger size samples have been fabricated by 70% thickness reduction of cold rolling for further study on the effect of annealing temperature and plastic deformation. The samples were completely conducted in the in-situ neutron diffraction study during heat-treatment and tensile deformation. Currently, the neutron diffraction data are being analyzed for the fraction of carbide precipitation, dislocation density and texture. The analysis result will be correlated to tensile properties. The recent result showed that, in a microstructure after 1178K, 1h annealing, the yield strength reached 481 MPa larger than that of C-undoped CoCrFeNi HEA (~200 MPa). The tensile ductility was also as large as ~45%.
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| Strategy for Future Research Activity |
The result indicated that an addition of interstitial C atoms and multiple-component solid solution led to large number of recrystallized grains and an inhibition of grain growth. Therefore, on the next research plan, the fabrication of nano-scaled structure for 1%C-doped CoCrFeNi HEA will be conducted by conventional thermo-mechanical process. Furthermore, the different type of carbide precipitation will be studied on the microstructure control of (CoCrFeNi)96Mo3C1 (at%). The addition of Mo is expected to increase a solid solution hardening and precipitation hardening with different carbide type.
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| Causes of Carryover |
The budget for Year 2022 was incurred in dealing with the cost of metallic alloy ingot production.
The incurring amount will be used for the consumable products for the experiment. On next fiscal year (Year 2023) the half of the budget will be spent for travel fee and conference fee. Therefore, the incurring amount can top up to other type of amount for conducting experiment.
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