基于局域应变分布分析的Ti/Al层状金属复合材料变形特性与强韧化机制研究

Strengthening metallic materials is the endless goal for materials science researchers. However, in most cases plasticity and toughness of metals decrease with increasing their strengths, and strength – plasticity (toughness) exhibits inverted relationship. Low plasticity and low toughness of high-strength metals weaken their industrial applications, and it becomes the bottleneck of development of materials science. Laminated architecture design of metals and their microstructures is an approach to solve the inverted relationship between strength and plasticity. Accordingly, strengthening and toughening of laminated metals will be achieved by controlling local strain concentration which will induce the plastic instability. In this project the Ti/Al laminated composite is used as the model to study the relationship of local strain distribution, deformed microstructure and macroscopic deformation behavior based on the measurement of local strain distribution and the characterization of deformed microstructure during plastic flow process. The laminated architecture and microstructure of the composite will be tailored by adjusting processing parameters (laminated parameter, rolling process and annealing, etc.) to fabricate some different composites with various microstructures and laminate scales. Then, the effect of laminated parameters and microstructure of the composites on the local strain distribution and interaction mechanism during plastic flow process will be analyzed to increase plastic deformability, and the strengthening-toughening mechanism of the Ti/Al laminated metal composite will be proposed. The finding of this project will enrich the theory of strengthening and toughening by configuration design of metal composites, and provide a basis for the design of high-strength and high-tough metallic materials.

强化金属材料是材料研究者不懈追求的目标，然而，大多数情况下，随强度升高，塑性和韧性下降，强度-塑性（韧性）呈倒置关系。高强度金属的低塑性低韧性削弱了其工业应用潜力，成为金属材料科学发展的瓶颈问题。层状结构设计是解决该问题的途径之一，通过控制局域应变集中导致的塑性失稳是实现层状金属材料强韧化的关键。本项目以Ti/Al层状复合材料为研究对象，从塑性变形过程产生的局域应变分布测量入手，表征变形过程的形变微结构（位错组态、界面结构、取向等），揭示“局域应变分布-形变微结构-宏观变形特性”间的关系，构建基于局域应变分析的宏观塑性变形表征方法。通过工艺参数（层状结构参数、轧制、退火）调整，制备层状结构与微观组织可控的Ti/Al层状复合材料，研究层状结构与微观组织对局域应变分布的影响规律，提高宏观塑性变形能力，揭示Ti/Al层状复合材料强韧化机理。丰富构型强韧化基础理论，为金属材料的强韧化设计提供依据。

现代工业技术发展对材料提出了轻质、高强度、高韧性的综合性能需求，如何克服材料强度上升时的塑性下降成为亟待解决的核心问题。构型化设计为克服这一难题提供了解决的思路。本项目以Ti/Al层状复合材料为研究对象，系统研究了其制备工艺，实现了对微观组织、结构参数均可控的层状复合材料的制备。开发搭建了基于光学显微镜、扫描电子显微镜、原子力显微镜的原位局域应变分布表征平台，并深入研究了Ti/Al层状复合材料变形过程中的应变演化规律，指出抑制应变局域化是层状结构材料强韧化的原因。搭建了基于同步辐射断层扫描技术的微裂纹表征平台，定量化统计分析了Ti/Al层状复合材料的微裂纹萌生和扩展行为，结果显示层状结构对于裂纹的扩展具有抑制作用，较高的裂纹容忍能力不仅增强了材料的韧性，更提高了材料在使役过程的安全性。结合同步辐射劳厄衍射技术及高能X射线衍射技术，本项目针对性开发了可用于金属材料塑性变形研究的数据分析软件。该技术可以在微米级的空间分辨率下对材料变形过程中微观组织演化及局域应力演化进行原位研究，为材料学研究提供了有力的新方法。对Ti/Al层状复合材料的研究结果表面，层状结构会约束组元的变形行为从而影响整体的力学性能。进一步研究表明组元反常变形行为的根源是与宏观加载条件差异较大的局域应力状态。局域应力是残余应力和加载过程中应力分配的综合结果，这一结果启示我们结构设计的本质是内应力的设计，可以通过组元的性质来调控内应力的演化，为新一代高强高韧材料的设计提供了新的思路。