Abstract
Realizing high work hardening and thus elevated strength-ductility synergy are prerequisites for the practical usage of body-centered-cubic high entropy alloys(BCC-HEAs).In this study,we report a novel dynamic strengthening mechanism,martensitic twinning transformation mechanism in a metastable re-fractory element-based BCC-HEA(TiZrHf)87Ta13(at.％)that can profoundly enhance the work hardening capability,leading to a large uniform ductility and high strength simultaneously.Different from con-ventional transformation induced plasticity(TRIP)and twinning induced plasticity(TWIP)strengthen-ing mechanisms,the martensitic twinning transformation strengthening mechanism combines the best characteristics of both TRIP and TWIP strengthening mechanisms,which greatly alleviates the strength-ductility trade-off that ubiquitously observed in BCC structural alloys.Microstructure characterization,carried out using X-ray diffraction(XRD)and electron back-scatter diffraction(EBSD)shows that,upon straining,α"(orthorhombic)martensite transformation,self-accommodation(SA)α"twinning and me-chanical α"twinning were activated sequentially.Transmission electron microscopy(TEM)analyses re-veal that continuous twinning activation is inherited from nucleating mechanical{351}α"type Ⅰ twins within SA"{351}"<(2)11>α"type Ⅱ twinned α"variants on[351}α"twinning plane by twinning transfor-mation through simple shear,thereby accommodating the excessive plastic strain through the twinning shear while concurrently refining the grain structure.Consequently,consistent high work hardening rates of 2-12.5 GPa were achieved during the entire plastic deformation,leading to a high tensile strength of 1.3 GPa and uniform elongation of 24％.Alloy development guidelines for activating such martensitic twinning transformation strengthening mechanism were proposed,which could be important in devel-oping new BCC-HEAs with optimal mechanical performance.
维普
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