放电等离子烧结块体纳米金属内部三维应力场分布研究

Spark plasma sintering (SPS) is a recently developed novel method for synthesizing bulk nano metals. However, the macro-micro internal stresses in the bulk nano metals synthesized by SPS process are relatively large due to the special characteristics of the SPS method (such as high heating rate, high cooling rate, high sintering pressure, and comparatively high nonuniform temperature distribution in the sintered materials), which may deteriorate the mechanical properties and reduce the service performances of the bulk nano metals. In the present study, the neutron diffraction method will be used to quantitatively measure the 3D stress fields in the bulk nano metals prepared by SPS process with different sintering parameters. Based on the measuring results, 3D stress distribution theory in the bulk nano metals will be established. An advanced micro self-consistent model used to anticipate the micro lattice strain and the macro stress-strain in the bulk nano metals will be developed and induced to the finite element program. Then the multiscale finite element method (MsFEM) will be employed to simulate the residual stress field in the bulk nano metals. Accordingly, the relation between the SPS parameters and the macro-micro internal stresses in the bulk nano metals will be revealed and an optimization design for the SPS parameters will be carried out. In addition, the action mechanism between the macro-micro internal stresses in the bulk nano metals and the micro defects of the bulk nano metals will be revealed based on investigating the stress of the third kind and the microstructure by XRD, SEM, TEM, and HRTEM analysis.

放电等离子烧结技术（SPS）是一种新型的块体纳米金属制备技术，但采用SPS技术制备得到的纳米金属中，存在很大的宏微观内应力，而这些内应力的大小、存在方式以及它们之间的相互作用对材料的力学性能及使用性能影响显著。本项目拟通过先进的中子衍射技术，对不同工艺参数条件下放电等离子烧结纳米金属内部的宏微观三维应力场进行定量测试与表征，建立纳米金属中包含宏微观应力场交互作用的三维应力场分布理论；在此基础上，构建能够预测微观点阵应变及宏观应力应变的先进自洽微观模拟模型，并将其引入有限元程序，对块体纳米金属内部的残余应力场进行跨尺度模拟，最终揭示块体纳米金属内部各种宏微观应力同SPS烧结工艺参数之间的关系，实现SPS工艺参数的优化设计。同时研究与各种缺陷相关的第三类应力分布及演化规律，并辅以XRD、SEM、TEM、HRTEM分析技术，揭示纳米金属内部宏微观应力场与材料内部各类微观缺陷的相互作用机制。

放电等离子烧结（Spark Plasma Sintering，简称SPS）技术，突破了传统的辐射加热方式，实现了粉体材料的内部发热与外部加热相结合，使烧结体的升温速率和降温速率均大幅度提高，极大地缩短了烧结时间，非常适合于纳米金属材料的制备。然而在采用SPS技术制备块体纳米金属的过程中，如果烧结工艺控制不当，将导致纳米金属制品中出现很大的宏微观残余应力，势必会对材料力学性能产生显著影响。针对这一问题，本项目通过对SPS制备三维块体纳米金属内部宏微观应力场进行定量测试与表征研究，建立了纳米金属中包含宏微观应力场交互作用的三维应力场分布理论，构建了纳米金属的微观力学本构关系，建立了纳米金属内部三维残余应力场的跨尺度模拟方法，实现了纳米金属微观力学行为与制备工艺参数及宏观力学行为之间关系的定量化研究，在此基础上揭示了纳米金属内部三维宏微观应力场与SPS各种关键制备工艺参数及材料内部各类微观缺陷的内在关系，最终实现了SPS工艺参数的优化设计，改善了块体纳米金属材料内部的残余应力场分布，提高了纳米金属的力学性能和使用性能。项目取得的研究成果将推动块体纳米金属制备技术相关基础理论研究工作的深入进展，并为三维纳米金属块体材料的工业化生产和应用打下了一定基础。