A novel immiscible high entropy alloy strengthened via L1_(2)-nanoprecipitate

The low-cost Fe-Cu,Fe-Ni,and Cu-based high-entropy alloys exhibit a widespread utilization prospect.However,these potential applications have been limited by their low strength.In this study,a novel Fe_(31)Cu_(31)Ni_(28)Al_(4)Ti_(3)Co_(3) immiscible high-entropy alloy(HEA)was developed.After vacuum arc melting and copper mold suction casting,this HEA exhibits a unique phase separation microstructure,which consists of striped Cu-rich regions and Fe-rich region.Further magnification of the striped Cu-rich region reveals that it is composed of a Cu-rich dot-like phase and a Fe-rich region.The aging alloy is further strengthened by a L1_(2)-Ni_(3)(AlTi)nanoprecipitates,achieving excellent yield strength(1185 MPa)and uniform ductility(~8.8%).The differential distribution of the L1_(2) nanoprecipitate in the striped Cu-rich region and the external Fe-rich region increased the strength difference between these two regions,which increased the strain gradient and thus improved hetero-deformation induced(HDI)hardening.This work provides a new route to improve the HDI hardening of Fe-Cu alloys.

纳米孪晶强化合金制备技术与力学性能研究进展

近年来,纳米孪晶强化由于在提高合金强度的同时还保持良好塑性的特点而受到研究者们的广泛关注。在纳米孪晶强化中,孪晶界是位错运动的二维界面障碍,这种界面障碍能够通过减少位错平均自由程来提升合金的加工硬化率和抗拉强度。此外,孪晶片层厚度与强化效果遵循Hall-Petch关系,孪晶片层厚度越小意味着孪晶界的密度越高,孪晶界和位错的相互作用将更加频繁。纳米孪晶强化技术已经被成功应用于多种合金体系。本文重点分析研究了高熵合金、TWIP钢、铝合金、铜合金和不锈钢中纳米孪晶强化技术的应用情况。首先,围绕纳米级变形孪晶和纳米级生长孪晶介绍了纳米孪晶的形成机理与制备方法。制备纳米级变形孪晶时,通常需要驱动肖克莱不全位错的运动;制备纳米级生长孪晶则需要控制微观局部应力集中和应力松弛,应力松弛使局部应力得到释放,进而形成低能的纳米级生长孪晶。然后,归纳了层错能对纳米孪晶形成的影响,概述了几种合金元素对层错能的影响规律,总结了评估层错能的四种方法,分析了温度和应变速率协调孪生机制的一般规律,即如何协调滑移-孪生两种机制的竞争关系,因此制备纳米孪晶需要协调好合金体系、层错能、温度、应变速率与孪生应力之间的关系。最后,讨论了纳米孪晶强化在力学性能方面的研究进展,与具有常规结构的材料相比,具有纳米孪晶结构的材料通常表现出更优异的力学性能,尤其是强塑性和断裂韧性。纳米孪晶甚至有望优化其他性能,将纳米孪晶引入到合金中有望为材料性能优化提供更多的机会。