超细晶CoFeCrMnNi高熵合金高温变形与断裂行为

The novel multi-component high-entropy alloys (HEAs) break through the shackles of the design concept for traditional alloys and open a new alloy world. The high mixing or configuration entropy in HEAs under a random mutually-miscible state can expand the solubility ranges of terminal solid solutions, resulting in a simple face-centered cubic (fcc) or body-centered cubic (bcc) crystal structure or their mixture. HEAs exhibits exhibit many superior properties to conventional alloys, and therefore have received increasing considerable attentions in recent decade. In this project, the optimal choice and match of principal elements, microstructural control and combination of strength and toughness will be firstly achieved for the single-phase CrMnFeCoNi high-entropy alloy on the basis of the empirical formation condition of HEAs and by thermomechanical treatments. The deformation characteristics of CrMnFeCoNi allys under tensile conditions with wide ranges of both strain rate and temperature will be examined to demonstrate the strain rate- and temperature-dependent strengthening mechanisms and their individual contribution to the strength and plasticity. The physical essence of component- and structure-dependent mechanisms for high temperature creep deformation will be elucidated for CrMnFeCoNi allys with a severe lattice distortion. Creep equations will be established to clearly characterize the dependence. Theoretical understandings and fundamentals are expected to be provided for improvement in both the high temperature tensile properties and creep resistance and the potential practical applications in near future for HEAs.

高熵合金作为新型多主元合金突破了传统合金设计理念的束缚, 开辟了合金新世界。随机互溶状态下高熵合金较高的混合熵可扩展端际固溶体的溶解范围, 从而形成简单的单相或复相固溶体结构。这种特殊的合金结构使得高熵合金具有优于传统合金的诸多性能和工业应用潜力而在近年来日益受到广泛关注。本项目基于高熵合金形成条件与热机处理，实现对单相固溶体CrMnFeCoNi高熵合金主元优化选配、微结构调控和较佳强韧配合。在此基础上，揭示多主元、不同晶粒尺寸合金高温拉伸变形特性，阐明各类应变率/温度依赖性强化机制及其对强韧性的贡献。澄清含晶格畸变超晶格单相高熵合金高温蠕变变形行为对主元和微结构依赖性的物理本质，建立能够清晰反映这种依赖性的蠕变方程。通过本项目研究，期望为高熵合金的高温拉伸力学性能和蠕变抗力的改善及其工程实际应用提供理论基础。

多主元高熵合金作为一种新型的合金材料，因其特殊结构引起的固溶强化、析出强化效应而表现出优异力学性能，具有重要的应用前景。 本项目系统研究了多主元AlxFeMnCrCoNi系单相及双相高熵合金的热机处理工艺、准静态/动态拉伸变形特性、高温蠕变与断裂机理。研究表明：.1. 经热轧退火处理，合金组织由偏析枝晶转变为晶粒尺寸可控的均匀等轴晶，其中细晶合金强度提高显著，合金强度的提高归因于固溶强化、晶界强化和沉淀强化等作用。.2. 合金在中温区的拉伸曲线出现依赖于变形温度和变形速率的锯齿流变特征，源于溶质原子对位错的“钉扎”，且作用机制与温度有关。.3. 该系合金表现出明显的动态拉伸应变速率响应特性，并可采用修正Johnson-Cook 本构方程予以描述和预测；高密度位错及其交互作用为动态变形微观结构的主要特征；随应变率和bcc相增加，合金断裂模式表现出由塑性到准解理转变。.4. 合金高温蠕变变形过程中的应力指数与激活能依赖于应力水平和Al含量，蠕变机制与变形微结构的演化和位错精细结构密切相关; 含铝合金蠕变行为对应不同温度区间表现出不同变形机制。. 上述结果有利于该类高熵合金的进一步强韧化与变形机理探索，为其工程应用提供有益参考。