B4C/Al(Al2O3)微纳分级复合材料的微区变形行为及细观力学原理

Particle-reinforced metal matrix composites (PRMMCs) with medium or high volume fraction (>30vol.%) are a kind of crucial engineering materials due to the combination of the structure and functional properties. However, the low ductility resulting from the addition of particles restricted the development and application of PRMMCs. Micro-/nano- dual-scale distribution of the reinforcement particles has been proven to be effective to achieve the balance between strength and ductility. The nanoparticles dispersed in the matrix can effectively relieve the stress concentration, and enhance the work hardening capability of the matrix, which allow us to tailor the strain partition and resist strain localization. However, due to the shortage of the fabrication techniques, the deformation behavior and the underlying mechanism still remain unclear for the micro-/nano- hierarchical PRMMCs. Based on the idea of module self-assembly, we have developed the flake powder metallurgy, and successfully fabricated the micro-/nano- hierarchical B4C/Al(Al2O3) composites with the effective balance between strength and ductility. Based on the previous study, this project intends to tailor the contents, particle size and distribution of micro/nanoparticles in B4C/Al(Al2O3) composites, investigate the impact of microstructural parameters on the stress transfer, strain partition, structure evolution and deformation behavior of the micro-/nano- hierarchical architecture, and reveal the micromechanics principle and related coupling mechanism in the micro/nano- hierarchical PRMMCs. This present project will provide the theoretical basis and technical routes for further investigation and optimization of strength and ductility in PRMMCs.

中高体积含量(>30vol.%)颗粒增强金属基复合材料(PRMMCs)是工业技术发展不可或缺的一类结构-功能一体化材料，但颗粒导致的低塑性已成为限制其发展应用的瓶颈。微纳双尺度颗粒分级复合构型可有效改善PRMMCs的强塑性平衡：纳米弥散相可有效缓解微米颗粒近界面微区的应力集中，并提高基体加工硬化能力，调控基体应变分配、抑制应变局域化。但限于现有技术制备分级结构的可调控性差，微纳颗粒协同作用下的微区变形行为和变形机理尚未得到揭示。为此，本项目提出了分级制备的思想，拟采用“片状粉末冶金”技术制备B4C/Al(Al2O3)微纳分级复合材料，通过对纳米和微米颗粒的含量、尺寸和分布等进行分级、精细调控，研究微结构参量对微区的应力-应变分配、位错演化和变形行为的影响规律，揭示微纳分级复合构型的耦合响应机制和细观力学原理，为PRMMCs的强塑性研究提供理论基础和技术途径。

本项目针对微米颗粒增强复合材料的低塑性问题，通过借鉴贝壳中高强韧、高模量的多级叠层复合构型效应，提出仿生复合/多级建构的新理念，将现有的“叠片粉末冶金”技术原型向基体合金化、复合多元化、构型多级化发展。实验与模拟结果表明，多峰晶粒结构设计能够有效的缓解应力和应变集中，从而防止裂纹过早萌生，使得多峰晶粒结构高的加工硬化率得以充分发挥。在多峰晶粒结构设计中，更加复杂的三峰晶粒结构比双峰晶粒结构具有更好的缓解应力和应变集中效果。纳米增强体的晶内化分布可以大幅提高超细晶的位错存储与增值能力，改善变形的均匀性从而同时提高强度和延展性。在微米增强体界面微区调控方面，引入具有仿矿物桥界面微凸起结构特征的界面，可以使增强体的载荷传递方式从单一的剪切应力传递向剪切应力与正应力相结合的方式转变，大幅提高其载荷传递能力，使得界面微区的塑性变形能力大幅提升。在上述研究的基础上，通过粉末基元组装技术研发出了具有UFG/CG基体异构、微纳混杂增强体异构的复合材料，相比同类型复合材料具有更优异的强度和延展性组合。这种新颖的多重构型化复合材料具有内在增韧和外在增韧的特点。作为内在增韧机制中，发现了UFG区域的位错储存能力增强、孪晶和异质变形诱导增韧。此外，纳米分散体引起的裂纹偏转和UFG/CG区域的裂纹抗性被认为是主要的外在增韧机制。本项目在解决基元组装-分级建构调控原理、复合组织和复合界面的形成演变规律、多尺度构型的构效关系和强韧化机理等关键科学技术问题的同时，初步建立了可工程化的复合制备与变形加工技术原型，具有重要的科学意义与实用价值。