| 研究実績の概要 |
High entropy alloys (HEAs) have attracted much academic attention, where the SFE of fcc-phase HEAs is the major factor determining the mechanical behaviors. The present study aimed to design novel HEAs with manipulated mechanical behavior via regulating the SFE, and then investigate the plastic deformation and fracture mechanisms. In FY 2019, we successfully designed various novel strong and ductile metastable fcc-phase HEAs, achieved by composition modification (reducing Fe and Ni meanwhile increasing Co content) and/or Mo-addition in fcc-phase quaternary-CoCrFeNi and quinary-CoCrMnNiFe systems with the assistance of ab initio and thermodynamics calculations. The results indicated that an increase in Co content and a decrease in Fe and Ni contents reduce the fcc phase stability and SFE, but enhance the elastic modulus, anisotropy, and lattice friction stress. A minor substitution of Co by Mo increases the lattice constant, but decreases the SFE and elastic modulus. The enhanced mechanical properties are due to the Mo-addition-induced strengthening accompanied with a low-SFE-induced restriction of planar behavior of dislocations, mechanical twinning, and strain-induced martensitic transformation. The research makes significant contributions to the basic understandings of the regulation of SFE and the manipulation of mechanical behaviors of HEAs, which sheds light on the development of next-generation high performance alloys.
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| 現在までの達成度 (区分) |
現在までの達成度 (区分)
2: おおむね順調に進展している
理由
The applicant proposed and conducted the researches based on previous study related to the strain-induced martensitic transformation behaviors in Cobalt-based alloys, where the Fe and Ni are fcc-phase stabilizers but Cr is the hcp-phase stabilizer. For the present study, we firstly conduced high-throughput ab initio and thermodynamics calculations, in order to obtain the guidelines for regulating phase stability and stacking fault energy. Then, we designed the high entropy alloys with enhanced mechanical properties and regulated plastic deformation behaviors, under the guidelines of calculations. The research was conducted with the combination of condensed matter theory and experimental, therefore, the research is progressing smoothly.
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| 今後の研究の推進方策 |
In the FY 2020, the following research will be conducted: 1. Investigate the influence of temperature on the value of stacking fault energies and the deformation behaviors of the novel designed alloys, by means of combining the theoretical calculations and experiments. 2. Investigate the detwinning and reverse martensitic transformation behaviors of the pre-deformed alloys, by in-situ TEM annealing and STEM-EDS/EELS analysis. 3. Investigate the effect of restoration of pre-deformed microstructures on the mechanical properties, where tensile test of the samples after de-twinning or reverse martensitic transformation will be conducted. Those studies make important contributions to the consummation of the phase transformation theories, which have significant potential impact on the development of the basic theories and applications of high entropy alloys.
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