放电等离子烧结脉冲电流加速的快速致密化动力学研究

The excellent sintering performance and rapid densification feature of spark plasma sintering (SPS) stems from the remarkably accelerated densification kinetics by pulse current. However, the mechanism of the enhanced densification by pulse current and the kinetics model are still unclear, which becomes a barrier to the understanding of sintering mechanism for a long time in academia. Our previous study on the non-thermal mechanisms of electric current demonstrated that the atomic diffusion and plasticity of metals. Nevertheless, the relatedness between the non-thermal effect and rapid densification is not clear. Based on this, the following scientific questions thus be proposed: first, atomic diffusion kinetics accelerated by pulse current; second, influences of electromigration on densification and the modeling of densification kinetics enhanced by electromigration; third, influence of electroplastic effect on the densification andthequantitative characterization of contribution of electroplastic; fourth, exactly modeling of densification kinetics by considering the electromigration and electroplastic effects of electric current and their weightinesses; simultaneously considering the difference between metal and ceramics. Based on the instruction of thermodynamic-kinetics theory of atomic diffusion, and the theory of electromigration and electroplastic, this project plans to take comprehensive research work on experiments and modeling of the non-thermal effect of current, so as to dissolve these scientific problems. Finally, this project is expected to obtain a quantitative densification kinetics model which synthetically incorporates the contribution of temperature, pressure and electric current, which providing a theoretical foundation for SPS application.

放电等离子烧结（Spark Plasma Sintering, SPS）优异高效的快速烧结特性，源于脉冲电流对致密化动力学的极大加速。然而，脉冲电流如何加速致密化的科学机制、动力学模型尚不清楚，长期困扰学术界对其深入认识，成为技术创新的瓶颈。申请人前期从SPS脉冲电流的非热效应出发，研究发现SPS电流极大加速原子扩散并提升塑性，然而非热效应的机制，与快速致密化的关联尚不明确。基于此，本项目拟解决以下科学问题：(1) 脉冲直流电加速原子扩散动力学；(2) SPS烧结电迁移效应及对致密化的影响机制；(3) SPS烧结电致塑性及对致密化影响的定量表征；(4) 考虑电迁移和电致塑性效应及其权重、及金属与陶瓷差异的致密化动力学模型。本课题以扩散动力学、电迁移和电致塑性等理论为指导，系统开展非热效应加速的SPS致密化动力学研究，获得综合考虑温度、压力、电流因素的精确致密化动力学模型，为SPS技术创新提供理论支撑。

本项目围绕以下四个方面对放电等离子烧结脉冲电流加速的快速致密化动力学展开了深入研究，建立相关模型，为材料的设计及研发提供了坚实的理论基础。.（1）直流/脉冲电场作用下电迁移加速的原子快速扩散动力学研究.项目通过热压烧结与SPS烧结纵向对比，SPS烧结参数中调解脉冲参数，研究不同烧结方式、不同电流模式作用下金属、合金、陶瓷等材料在致密化过程中的原子扩散行为及扩散动力学。发现对于置换扩散类型，流加速扩散的机制为电流的电迁移效应；对于反应扩散体系，电场可以提高原子互扩散系数而互扩散激活能显著降低。.（2）电迁移对快速致密化的影响行为及定量表征.项目以蠕变理论为基础，结合成熟的电迁移理论，建立了粉末SPS中后期的致密化动力学模型。该模型将温度、压力和电流视为致密化主要的三大驱动力，其中电流对致密化的主要作用机制为电迁移。.（3）电致塑性效应规律及对对致密化加速机制.项目研究了不同电流模式，即连续直流模式（DC）和脉冲直流（PC），对金属及合金的致密化行为的影响。发现相同烧结条件下，在扩散控制致密化阶段（stage 1），DC的致密化速率高于PC的致密化速率；而在位错控制致密化阶段stage 2， DC烧结的样品的致密化率小于PC。对于位错控制阶段（stage 2），电迁移并不是电流唯一的非热作用机制。.（4）基于电迁移、电致塑性效应的统一的SPS 快速致密化动力学模型建立及实证.项目以蠕变和电迁移理论为框架，建立了粉末烧结中后期温度、压力和电流多场耦合作用的致密化动力学模型。并以该模型为基础，揭示了SPS粉末致密化过程的动力学行为。通过对致密化动力学模型的计算发现，温度和压力对SPS过程的致密化起到了主要的贡献，而电流对致密化贡献相对较小。SPS烧结过程中，三大驱动力对致密化贡献大小的主次关系分别为压力˃温度˃电流。致密化中后期的恒温阶段，温度压力升高对致密化速率提高没有贡献，电流是致密化唯一的正驱动力。