微纳结构CoCrFeNi基高熵合金粉末冶金制备及强韧化机理研究

Strengthening and Toughening Mechanism of Heterogeneous Structured CoCrFeNi Based High Entropy Alloy Prepared by Powder Metallurgy

针对CoCrFeNi基高熵合金强塑性失配问题,提出了基于高能球磨、放电等离子体烧结和热挤压相结合的粉末冶金制备方法,探究了制备工艺参数对晶粒尺寸、第二相颗粒和孪晶组织演变的影响规律,分别制备出由粗晶、细晶和纳米颗粒构成的多尺度异构CoCrFeNiMnTi_(0.2)高熵合金,以及包含超细晶、纳米颗粒和纳米孪晶的CoCrFeNiMnTi_(0.2)高熵合金。拉伸力学性能显示,两种高熵合金屈服强度和断后伸长率分别高达1298 MPa和13%,以及1507MPa和7%,均实现了较好的强塑性均衡。最后,基于对霍尔佩奇系数修订,建立了纳米颗粒增强超细晶CoCrFeNi基高熵合金强化模型,揭示了纳米颗粒与微纳异构组织耦合强韧化机制,以及超细晶、纳米颗粒与纳米孪晶协同强韧化机理,并进一步发现纳米孪晶能够增加高熵合金流变应力,使新的变形孪晶形核,从而诱发多级变形行为。

In this study,a microstructure control strategy by combining powder high-energy ball milling,spark plasma sintering and hot extrusion was proposed.The influence of preparation process parameters on the evolution of grain size,second phase particles and twins was investigated.A CoCrFeNiMnTi_(0.2) high entropy alloy with multi-scale heterogeneous microstructure containing coarse grains,fine grains and nanoparticles,and a CoCrFeNiMnTi_(0.2) high entropy alloy consisting of ultrafine grains,nanoparticles and nano-twins were prepared.The tensile mechanical properties showed that the yield strength and elongation to fracture of the high entropy alloys were up to 1298 MPa and 13%,and 1507 MPa and 7%,respectively,achieving a good trade-off between strength and plasticity.Lastly,based on the revision of the Holpage coefficient,a strengthening model for nanoparticle reinforced ultrafine grain CoCrFeNi-based high entropy alloy was established.A new coupling mechanism between nanoparticles and heterogeneous structure,as well as a synergetic mechanism of ultrafine grains,nanoparticles and nano-twins were discussed.It was also found that nano-twins could increase the flow stress of high entropy alloy,resulting in multi-level deformation behavior by inducing nucleation of new deformation twins.