Mo微合金化与原位石墨烯协同强韧镍基复合材料的界面特性及相关力学行为

Owing to the agglomeration of graphene, and the poor interfacial bonding between the graphene reinforcements and nickel matrix, the strength-ductility trade-off has restricted the development of the graphene/Ni composite. This project puts forward a research idea to improve the strength and ductility of the graphene/Ni composite by the synergy between the micro-alloying in metal matrix and in-situ grown graphene. The molybdenum (Mo) element, which can significantly reduce the stacking fault energy of pure nickel, will be selected to the micro-alloying of nickel powders. The graphene will grow on the nickel particles by an in-situ method, then the bulk graphene/Ni composites will be fabricated by the spark plasma sintering process. First, the dependency of the phase compositions, microstructures, and interfacial structure of the composites on the Mo concentration will be investigated. The change regulation of the interfacial bonds and characteristics between the graphene and nickel matrix after the addition of Mo element will be explored. The influences and mechanism of Mo content on the interface binding of the graphene-Ni interfaces will be revealed. Second, the corresponding relations of contents, structure, tensile mechanical properties and fracture characteristics of the composites will be clarified. Then based on the plastic deformation behaviors and failure mechanisms, the effects and mechanisms of Mo element on the strength and ductility of the in-situ graphene/Ni composites will be discussed. At last, a matching criterion of the constituents and microstructures in graphene/nickel composites with high strength and good ductility will be proposed. The results can provide a guide to design and fabricate high-performance nickel matrix based composites.

目前石墨烯增强镍基复合材料的研究中存在着由于石墨烯分散性差和石墨烯/镍界面结合强度低引起的强度-塑性倒置关系突出问题。为此，本项目提出利用微合金化与原位石墨烯协同作用来强韧镍基复合材料的思想，拟选取能显著降低镍基体层错能的Mo元素对镍颗粒进行微合金化处理后原位生长石墨烯，再将复合颗粒通过放电等离子烧结获得石墨烯/镍复合材料；研究复合材料物相、显微组织、界面结构与Mo含量的关联性，考察Mo元素作用下石墨烯与镍基体间界面结合状态及特征的演变规律，明确Mo元素对原位石墨烯/镍复合材料界面结合行为的影响及作用机制；研究复合材料组分、微观结构、力学性能及断裂特征的对应关系，结合复合材料的塑性变形行为和失效机理分析，探讨Mo元素对原位石墨烯/镍复合材料增韧补强的作用效果与机制，提出具有高强度、高韧性的石墨烯/镍复合材料的组分与结构设计原则，为发展高性能的镍基复合材料提供理论基础和参考依据。

本项目在明确镍合金颗粒表面高质量石墨烯增强相的生长条件与形成机理、原位自生石墨烯增强相影响镍基复合材料力学性能的规律及其强韧化机理的基础上，通过Mo元素对原位石墨烯/镍复合材料进行微合金化处理，系统研究了Mo元素含量对复合材料显微组织、界面结构和力学性能的影响规律，揭示出Mo元素作用下原位石墨烯/镍复合材料的塑性变形机制和失效机理。研究发现随着Mo元素添加量（0.1 wt.%～1.0 wt.%）的增加，镍基体中因层错能降低而形成的退火孪晶比例逐渐增大。同时，Mo元素的晶界偏析也导致石墨烯/镍界面区生成钼碳化物，复合材料界面由机械结合机制向化学结合机制转变。与原位石墨烯/镍复合材料中位错滑移主导的塑性变形机制不同，在Mo元素的影响下，复合材料呈现出位错滑移和孪生变形共同作用的特征，并在拉伸过程中以韧性断裂方式失效。总体来看，Mo元素添加后原位石墨烯/镍复合材料的强度和塑性均得以改善，并在Mo含量0.2 wt.%时表现出最佳的强度-塑性匹配。这主要归因于：（1）Mo元素能够通过降低镍基体层错能来提高石墨烯/镍复合材料的加工硬化能力。一方面，层错能的降低可以增加位错平面滑移能力，降低位错交滑移倾向及湮灭距离，实现晶界区高位错密度的存储；另一方面，低层错能镍晶粒具有更高的层错和孪晶萌生能力，使得塑性变形过程中镍基体中层错与孪晶变形加强，产生孪生诱发塑性及动态Hall-Petch效应。（2）适量的Mo元素可以通过向晶界偏析来形成界面反应层，在不损伤石墨烯结构的前提下，提高其与镍基体之间的界面结合强度。在拉伸过程中，适宜强度的界面能够将载荷有效传递至石墨烯增强相承载，提高复合材料的强度。（3）原位石墨烯/镍复合材料中超大比表面积的石墨烯增强体可以在材料断裂过程中形成裂纹桥联和拔出效应，孪晶则能够钝化裂纹尖端，阻止裂纹扩展，提高其断裂韧性。项目研究探明了Mo元素作用下原位石墨烯/镍复合材料化学组分-微观组织-界面结构-力学性能的映射关系，阐明了Mo元素微合金化对原位石墨烯/镍复合材料增强补韧的作用效果与机制，能够为高强度高韧性镍基复合材料的开发提供理论依据和实验参考。