激光成形颗粒增强镍基高温合金多相复合与梯度界面协同强韧化机理

The incorporation of ceramic reinforcing particles in Ni-based superalloys is an efficient method to improve their high-temperature mechanical performance. However, due to the limited wettability between ceramics and metals and the significant difference in coefficients of thermal expansion, the interfacial residual stress and microcracks are prone to present. Furthermore, the addition of ceramic reinforcing phase in Ni-based superalloys tends to decrease the controllability of compositions and microstructures of γ matrix phase and γ’(γ’’) reinforcing phase. The above factors are responsible for the decrease in the ductility and plasticity of laser formed parts. In the present project, the gradient interface is tailored between ceramic reinforcement and matrix via the control of laser processing parameters and components of composite materials. The interfacial residual stress, interfacial micropores and microcracks can be controlled and eliminated, hopefully resolving the contradiction between strength and ductility of laser formed composites parts. The formation mechanism, microstructure and performance of laser formed gradient interface are studied and the influencing mechanisms of material and process factors are assessed. The microstructural developments of ceramic reinforcing phase, γ’(γ’’) phase, and γ phase at different laser processing parameters are investigated and the control methods of interior metallurgical defects are proposed. The load-bearing properties and mechanical behaviors of the gradient interface under various types of loads and operating temperatures are studied and the transfer and distribution rules of internal stress inside the parts are elucidated. The stress-induced movement and propagation mechanisms of dislocations inside the materials are investigated and the interaction rules of dislocations with reinforcing phases and interfaces are studied, proposing the strengthening and toughening mechanisms of laser formed parts. This project is expected to provide the scientific basis for laser additive manufacturing of high-performance Ni superalloy based composites parts with controlled structures and properties.

在Ni基高温合金中复合陶瓷增强颗粒，是提高其高温力学性能的有效途径，但陶瓷/金属润湿性差、线膨胀系数差异大，易导致界面残余应力及裂纹，且添加陶瓷相使基体相γ和强化相γ’(γ’’)成分和组织可控性变差；这是激光成形件韧性和塑性下降的主因。本项目通过激光工艺参数和复合材料组分调控，可在陶瓷增强体与基体间形成梯度界面层，控制并消除界面残余应力、界面微孔及微裂纹，有望解决复合材料零件“强”与“韧”的矛盾。研究激光作用下梯度界面形成机制、显微结构、界面性能及材料和工艺影响机理；研究陶瓷相、γ’(γ’’)及γ相显微组织随激光工艺参数的演变规律及内部冶金缺陷控制方法；研究各种载荷和温度下梯度界面承载特性、力学行为及内应力传递与分布规律；研究应力作用下材料内部位错运动和增殖机制以及与增强相和界面作用规律，揭示激光成形件强韧化机理。本项目可为高性能Ni基高温合金复合材料零件激光控形控性增材制造提供科学基础。

陶瓷颗粒复合增强是提升镍基高温合金综合力学性能的重要途径之一，可使材料具有更高的比强度、比刚度及耐热性。选区激光熔化增材制造技术可实现高性能材料和高精度构件一体化成形，但仍存在增强相与基体间界面裂纹、多相显微组织复杂多变、强度与韧性难以协同提升等尚未解决的科学难题。本项目从陶瓷增强镍基复合材料熔池热力学、激光工艺参数调控、增强相/基体梯度界面设计、增材制造形性调控等四方面开展研究，成果如下：（1）研究了选区激光熔化陶瓷增强镍基复合材料熔池熔体及异质界面的热力学行为，揭示了粉末特性及铺放行为对介观尺度熔池热力学及粉体熔凝特性作用机制，发现了增加激光能量密度可提高增强相/基体界面温度、温度梯度及熔体流速，明晰了增强相-界面-基体间传热传质机制；（2）研究了选区激光熔化镍基复合材料冶金缺陷演变规律及工艺调控方法，发现了激光成形件致密度随激光功率、扫描间距及粉末粒径的增大呈先增后减的变化规律，揭示了激光工艺参数对熔体润湿铺展行为及成形件表面粗糙度的影响规律，基于粉体特性及工艺参数优化实现了成形致密度提升及冶金缺陷控制，并在微/纳多尺度结构下实现了构件表面超疏水特性；（3）研究了激光增材制造镍基复合材料梯度界面设计及组织和裂纹调控方法，发现了增强相/基体间梯度界面可显著改善界面润湿行为，平衡陶瓷/金属物性差异，并起到传递载荷和阻止裂纹扩展的作用，构筑了基于梯度界面设计来抑制界面缺陷、提升界面性能的普适性方法；（4）研究了激光增材制造镍基复合材料显微组织演变规律及强韧化机制，发现了基于激光工艺参数、梯度界面设计及热处理工艺调控可使成形构件强度和韧性协同提升，揭示了激光增材制造镍基梯度界面复合材料的强韧化机制及其材料和工艺影响机制。本项目提出的基于复合材料梯度界面调控实现构件强度和韧性协同提升的原理与方法，可为航空航天等领域高性能陶瓷增强镍基高温合金构件激光控形与控性增材制造提供科学指导。