The mechanical properties and deformation mechanisms of a newly developed Co-free FeMnSiNiAl high entropy alloy (HEA) at room and cryogenic temperatures were systematically investigated. The initial tensile deformation at room temperature was dominated by dislocation slipping, with modest strengthening from the Transformation-Induced Plasticity (TRIP) effect due to the deformation-induced FCC → HCP martensitic transformation. Subsequently, the TRIP effect was markedly enhanced during the middle and later stages of deformation, leading to an excellent combination of yield strength (σy, 315.1 MPa), ultimate tensile strength (σu, 773.4 MPa), and fracture elongations (εf, 78.3 %). The strengthening by the TRIP effect was significantly enhanced at cryogenic temperatures as a result of enhanced FCC → HCP martensitic transformation. This resulted in a synergetic improvement in strength and ductility at 223 K, with σy of 363.6 MPa, σu of 832.1 MPa, and εf of 87.2 %. The enhanced ductility at 223 K was linked to the FCC → HCP → BCC sequential martensitic transformation during the middle and later stages of deformation, which acted as an additional way to accommodate plastic strain and delay strain localization. However, the rapid FCC → HCP transformation at the early stage of deformation at 173 K and 77 K impeded the FCC → HCP → BCC sequential martensitic transformation during subsequent deformation stages, thus remarkably enhancing strength but reducing ductility. Our findings provide new insights into the design and development of TRIP-assisted single-phase FCC HEAs for cryogenic applications.

中文翻译：

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FeMnSiNiAl 高熵合金的低温变形强化机制


系统研究了新开发的无钴 FeMnSiNiAl 高熵合金 （HEA） 在室温和低温下的力学性能和变形机制。室温下的初始拉伸变形以位错滑移为主，由于变形诱导的 FCC → HCP 马氏体相变，相变诱导塑性 （TRIP） 效应略微增强。随后，在变形的中后期，TRIP 效应显著增强，实现了屈服强度 （σy， 315.1 MPa）、极限拉伸强度 （σu， 773.4 MPa） 和断裂伸长率 （εf， 78.3 %） 的完美组合。由于增强的 FCC → HCP 马氏体转变，TRIP 效应的强化在低温下显着增强。这导致在 223 K 时强度和延展性协同提高，σy 为 363.6 MPa，σu 为 832.1 MPa，εf 为 87.2 %。在 223 K 时增强的延展性与 FCC → HCP →变形中后期的 BCC 顺序马氏体转变有关，这是适应塑性应变和延迟应变定位的另一种方式。然而，在 173 K 和 77 K 变形初期，FCC→HCP的快速转变阻碍了FCC→HCP→随后变形阶段BCC的连续马氏体转变，从而显著提高了强度，但降低了延展性。我们的研究结果为用于低温应用的 TRIP 辅助单相 FCC HEA 的设计和开发提供了新的见解。