短程有序对不同层错能FCC高熵合金变形行为的影响

Usually, when the strength of metals increases, the plasticity decreases. In the present project, the short range ordering is used to increase the strength and plasticity of FCC high entropy alloys, since the short range ordering can improve the critical shear stress of dislocation movement and is in favor of the formation of deformation twins. In order to control and change the short range ordering and stacking fault energy of the CrMnFeCoNi and AlxCoCrFeNi alloy systems, the effect of heat treatment and alloys component on the short range ordering and stacking fault energy will be analyzed. Then, the relationship between short range ordering, stacking fault energy and the choice of deformation mechanisms including cross slipping, planar slipping and twining will be studied by using of TEM. The results can break through the limit that only stacking fault energy was considered during analyzing the deformation behavior of traditional FCC metals. In order to reveal the effect of short range ordering on the microstructure evolution of FCC high entropy alloys with different stacking fault energies during deformation process, the dislocation configuration, Burgers vector of dislocations, dislocation density, type of twin boundaries, lamellar thickness and fraction of twins, and interaction of dislocations and twin boundaries will be characterized by using of OM, ECCI, EBSD, XRD and TEM. Meanwhile, according to the results of tensile test under different temperatures, the effect of short range ordering on mechanical properties of FCC high entropy alloys with different stacking fault energies will be analyzed. The results can lay the theoretical foundation for preparing high entropy alloys with high strength and plasticity.

金属材料的强化通常以牺牲塑性来提高强度，本项申请提出利用短程有序增加位错运动的临界切应力以及促进变形孪晶形成的特性，来提高FCC高熵合金的屈服强度和塑性。研究热处理对CoCrFeMnNi和AlxCoCrFeNi两种FCC高熵合金体系短程有序的影响，考察合金组元对短程有序和层错能的影响。采用TEM等技术，分析高熵合金的短程有序、层错能与位错交滑移、平面滑移和孪生等变形机制选择的相关性。采用OM、ECCI、EBSD、XRD及TEM等技术，研究变形FCC高熵合金位错组态、柏氏矢量、位错密度、位错与孪晶的交互作用、孪晶类型、孪晶片层厚度和体积分数等，明确短程有序对不同层错能FCC高熵合金变形组织演变的影响。结合不同温度的拉伸结果，明确短程有序对不同层错能FCC高熵合金力学性能的影响规律。通过本项研究，不仅可为制备高强度、高塑性高熵合金奠定理论，还能突破传统FCC金属仅用层错能调控变形机制的局限。

金属材料的强化方式主要有第二相强化、弥散强化、形变强化、细晶强化等，但这些强化方式主要以牺牲材料的塑性来提高强度。本项提出利用短程有序增加位错运动的临界切应力以及促进变形孪晶形成的特性，来提高FCC高熵合金的屈服强度和塑性。具体内容包括明确热处理和合金组元对FCC高熵合金短程有序的影响规律，揭示合金成分与层错能之间的关系，系统分析高熵合金的微观变形组织，深入研究短程有序对不同层错能FCC高熵合金变形机制和力学性能影响的微观机理。取得的重要成果如下：.（a）明确了C对CoCrFeMnNi高熵合金组织和性能的影响规律。C含量低时，随着C含量的增加，合金晶粒尺寸越小，晶格常数越大，强度和塑性同步提高，主要是固溶强化；针对非等原子比Fe50Mn30Co10Cr10高熵合金进行C和Mo原子合金化，调控合金的层错能，得到TWIP/TRIP高熵合金。.（b）针对CoCrFeMnNi高熵合金，添加Al，且取缔易与C和B易形成陶瓷相的Cr，Mn元素，使得合金形成固溶体。添加B至CoFeNiAlBx合金中，其枝晶组织逐渐减少，枝晶间组织逐渐增多。枝晶间组织逐渐由“细长条状FCC及其上分布的颗粒状”变为由富Fe的FCC1和富Fe、Co和B的FCC2结构组成的共晶组织，而合金枝晶组织为富Al和Ni元素的短程有序B2结构。.（c）调控高熵合金成分形成延塑性较好的FCC基高熵合金Al-Co-Fe-Ni-C。形成高体积分数的短程有序强化相(κ′相)，合金强度显著提高。变形主由孪晶和平面滑移协调变形，转变为位错切过短程有序相以及平面滑移。由于短程有序相的形成发生在凝固阶段，合金通过直接凝固就能形成单峰分布的纳米共格高温强化相。.这些问题的解决不仅可为制备高强度、高塑性高熵合金奠定理论基础，还能进一步丰富塑性变形理论，本项研究具有重要的科学理论意义和工程实用价值。