2023 Fiscal Year Research-status Report
Microstructure control of biocompatible BCC high entropy alloys for achieving bone-like Young's modulus
| Project/Area Number |
23K13574
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| Research Institution | Yokohama National University |
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Principal Investigator |
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| Project Period (FY) |
2023-04-01 – 2025-03-31
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| Keywords | High entropy alloy / Medium entropy alloy / Texture / Biomedical material / Hot deformation / Elastic modulus / Microstructure |
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| Outline of Annual Research Achievements |
A new single-BCC NbTiZr-based medium entropy alloy with additions of Cr and Mo was developed for biomedical implants. The alloy presents low density (~6.6 g/cm^3), high yield strength (~950 MPa) as well as non-cytotoxic based on a study of cell viability. A further reduction of Young’s modulus close to human bone is controlled by a development of <001> preferential dynamic grain growth via a high temperature uniaxial compression. Based on current result, the dynamic grain growth was observed, but texture was not distinctively developed. The larger volume fraction of <001> texture leads to lower Young's modulus. The alloy could be fabricated to have the lowest Young’s modulus at ~70 GPa. The result indicates that the alloy can be potentially developed for the biomedical applications.
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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
The microstructure and texture development of NbTiZr-based MEA with additions of Cr and Mo through hot deformation was successfully characterized and understood. Although the Young's modulus could be reduced, the <001> preferential dynamic grain growth was not sharply developed for significantly reducing the Young's modulus. It indicates that grain boundary migration and <001> preferential dynamic grain growth were not highly activated under current process conditions. Moreover, the sluggish diffusion resulted from mutual interactions of compositional elements is considered to retard the grain growth. The results and outcomes can provide a key solution for designing new process conditions and alloy compositions in order to achieving bone-like Young's modulus.
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| Strategy for Future Research Activity |
To drive the <001> preferential dynamic grain growth in BCC medium-high entropy alloys, the new alloy compositions with new trace element (Ta) will be conducted with hot uniaxial compression under potential process conditions. The addition of new trace element (Ta) is expected to increase grain boundary migration and enable the <001> preferential dynamic grain growth. The process conditions should be properly designed for driving the distinctive texture development. Moreover, the biocompatibility examinations will be conducted on the new alloys. The best alloy composition and process conditions can be suggested for being used as biomedical implant.
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