激光冲击强化高熵合金循环变形行为的宏微观实验与本构理论研究

High entropy alloys (HEAs) break up the shackles of concept that the traditional alloys mainly contain two elements at most. A new philosophy of material design from the point of "entropy" in thermodynamics enables the excellent mechanical performances of HEAs, which are expected to break through the limits of traditional materials. Laser shock peening (LSP) is a new surface strengthening technology. It can change the microstructure of surface material and produce residual compressive stress at a thick enough depth. Therefore, the anti-fatigue performance of materials will be significantly improved by LSP. However, no researches have been done towards the cyclic deformation behavior of high entropy alloy treated with laser shock peening. This project focus on the non-equiatomic high-entropy dual-phase alloys Fe50Mn30Co10Cr10 (at%), and the macroscopic mechanical experiments, microstructural characterizations, and constitutive modeling will be systematically developed. Through this project, we will reveal the cyclic deformation features of HEAs and the evolution laws of microstructures, elaborating the relationships among microstructure, deformation mechanism and cyclic response. Finally, a constitutive model comprehensively considering multiple plastic deformation mechanisms (such as dislocation slipping, twining, phase transformation and so on) will be established, and the effect of gradient microstructures and residual compressive stress resulting from LSP on the cyclic plastic behavior of HEAs will also be considered in this model. This project will benefit the development of the research direction of material constitutive modelling in solid mechanics, and furthermore promote the engineering application of HEAs by providing the theoretical basis for the strength-ductility optimization and anti-fatigue design.

高熵合金突破了传统以“1-2种元素为主”的合金概念的束缚，从热力学"熵"的角度创新了材料的设计理念，具有优异的力学性能，有望突破传统材料的极限。激光冲击强化是一种新的表面强化技术，可显著提高结构材料在循环载荷作用下的疲劳性能，但激光冲击强化高熵合金的循环变形研究尚未见报道。本项目以非等原子比双相高熵合金Fe50Mn30Co10Cr10为研究对象，系统开展宏观力学实验、微结构表征、本构理论建模等方面的研究，揭示其变形特征及微结构演化规律，阐明高熵合金的微观组织-变形机理-循环响应之间的关联，建立综合考虑位错、孪生和相变等多种塑性变形机制以及激光冲击强化导致的梯度微结构和残余应力对高熵合金循环塑性响应影响的本构模型。本研究将促进固体力学学科材料本构关系研究领域的发展，为高熵合金的强韧化设计和抗疲劳设计提供理论基础，进而促进高熵合金的工程应用。

高熵合金材料的变形多机制和激光冲击强化的表面纳米化微结构是提升材料力学性能的重要途径，可实现材料的强塑性兼得，有必要深入揭示高熵合金材料的多机制变形机理和激光冲击强化梯度微结构对材料力学性能的调控机理，建立基于变形机制和微观结构的本构模型来进一步指导高强高塑材料的设计和安全服役。本项目系统开展了高熵合金材料的制备、表面纳米化处理、宏观力学实验、微结构表征、原子尺度模拟和本构理论建模等方面的研究，揭示材料变形特征及微结构演化规律，阐明“微观组织-变形机理-力学响应”之间的关联关系。在材料制备方面，表面纳米化处理高熵合金的屈服应力比处理前提升了32.6%，而韧性仍保持在45%以上。力学性能测试方面，发现了高熵合金具有更强的循环硬化效应和抵御塑性累积的能力。分子动力学模拟方面，揭示了激光冲击导致的弹塑性双波分离和层裂现象、以及梯度高熵合金单拉响应的额外强化机制和循环响应的包辛格现象。本构建模方面，建立了基于变形多机制的高熵合金晶体塑性本构模型，刻画了高熵合金晶粒尺寸和温度相关的单拉力学性能，以及孪生和相变相关的循环塑性棘轮现象，以及各种梯度微结构（梯度晶粒、梯度相、梯度位错）对高熵合金强韧行为的影响。在项目执行期，共发表论文42篇，培养博士毕业生1名，硕士毕业生3名，本科毕业生8名。本项目取得的研究成果丰富了对高熵合金和激光冲击强化的认识，为高强高塑材料的微结构调控、性能优化和工程服役提供了理论参考，具有重要的科学意义和潜在的工程应用前景。本研究将促进固体力学学科材料本构关系研究领域的发展，为高熵合金的强韧化设计和抗疲劳设计提供理论基础，进而促进高熵合金的工程应用。