高压扭转变形诱导的非均匀微观结构演化

Heterogeneous Microstructural Evolution Induced by High-pressure Torsion

高压扭转变形可以在数个吉帕的压强条件下对金属材料施加理论上无上限的应变量,可以有效地将粗晶材料细化成超细晶甚至是纳米晶材料,是迄今为止极高效的制备块体纳米金属材料的技术之一。然而,其碟形的样品设计和扭转式的应变施加方式导致了材料塑性变形时复杂且非常不均匀的微观结构演化,进而影响了变形后材料的力学性能及后续的使用和再加工。因此,深入理解高压扭转变形导致的微观结构不均匀性,对该技术的研发、变形材料的工业化应用以及后续的加工工艺设计有着重要的指导意义。本文基于双相材料中应变视觉化的实验成果,介绍并分析了金属材料的非均匀结构演化机制和约束条件下的塑性失稳现象,归纳总结了宏观应变梯度和微观应变梯度对微观结构演化和塑性失稳的决定性作用,最后对高压扭转技术制备纳米材料的应用与发展进行了展望。

High-pressure torsion(HPT)can impose a high pressure of a few gigapascal and theoretically unlimited strain to metallic materials.As a result,HPT can effectively refine the grain sizes of metallic materials to ultrafine-grained regime and even nanocrystalline regime.Therefore,HPT is considered one of the most effective methods for processing bulk nanostructured materials.However,owing to the disk-shaped specimen used and the torsional strain imposed by HPT,heterogeneous microstructural evolution is induced in the metallic materials.The microstructural heterogeneity has a direct impact on the mechanical properties of materials.Therefore,in-depth understanding about heterogeneous microstructural evolution induced by HPT is crucial for the future development of HPT related techniques and applications of the materials processed by HPT.In the review,the representative shear strain patterns induced by HPT are reassessed;microscopic heterogeneities and plastic instabilities abound in the microstructural evolution processes are discussed;the concept of strain gradient plasticity has been adopted to explain the heterogeneous microstructural evolution.Finally,we prospect the application and development of HPT related techniques for processing nanostructured and hetero-structured materials.