Field-activated sintering of metallic materials - experimental study and simulation of mechanisms of matter transport

提出的研究项目旨在准确阐明和描述金属粉末在场激活烧结（FAST）过程中发生的烧结过程。在这个项目中，温度、压力、温度梯度、电场和电流密度对材料输运过程的影响将被研究。为了做到这一点，进行了大量协调的理论/数值和实验研究。所提出的项目以批判性的方式审查文献中关于热扩散和电迁移的常见假设。在第一个项目阶段取得相当大进展的基础上，第二个项目阶段的目标是开发和彻底描述FAST过程。该描述将能够捕获FAST过程中依赖于当前环境条件的相关材料和粉末特性的传输机制。因此，需要明确地解决烧结过程中的材料传输问题，并将其包含在电热-热力模型中。该项目实验部分的主要工作包包括烧结实验，采用针对所研究金属材料的工艺参数的系统变化。数值模型的开发将在固体力学研究所（IFKM）完成，实验将在德累斯顿工业大学材料科学研究所（IfWW）进行。主要目标是开发和实现能够模拟FAST过程中颗粒接触增长和致密化的有限元模型。这必须考虑到曲面和外部压力以及温度和电势的梯度，它们是物质传输过程的驱动力。通过将数值模拟结果与专门设计的实验结果进行比较，验证了有限元模拟结果，进而预测了相关输运机制，从而实现了FAST工艺参数的优化。特别是对任意导电材料的场辅助烧结有较好的认识。在项目预期结果的基础上，将首次全面描述金属粉末系统在FAST过程中发生的致密化过程，包括材料、粒度、表面质量、压力、温度和电气制度的影响。将模型系统的假设转移到实际粉末系统中，可以更可靠地设计致密化和微观结构的演变。此外，对FAST过程的科学合理描述应取代既没有数值证据也没有实验证据支持的猜测。

The proposed research project aims at the accurate elucidation and description of the sintering processes occurring during field activated sintering (FAST) of metallic powders. Within this project, the influence of temperature, pressure, temperature gradient, electric field and electric current density on the material-transport processes will be investigated. In order to do this, a multitude of coordinated theoretical/numerical and experimental investigations is conducted. The proposed project serves to review common hypotheses given in literature concerning e.g. thermodiffusion and electromigration in a critical manner.On the basis of the considerable progress made during the first project phase, the second project phase aims at developing and thoroughly describing the FAST process. This description will be capable of capturing the transport mechanisms during the FAST process for relevant material and powder properties in dependence of the present ambient conditions. As a result of this, the material transport during the sintering needs to be addressed explicitly, and will be included in the electro-thermo-mechanical model. The major work package of the experimental part of the project consists of sintering experiments employing systematic variations of the process parameters which are adapted regarding the investigated metallic materials. The development of the numerical model will be done at the Institute of Solid Mechanics (IFKM) and the experiments will be conducted at the Institute of Materials Science (IfWW) at TU Dresden. A major goal is the development and implementation of a finite-element model capable of modeling the growth of the particle contact and the densification during the FAST process. This has to be done under consideration of curved surfaces and external pressure as well as gradients of temperature and of electric potential, which are the driving forces of the material transport processes. By comparing the results of the numerical simulation with the specifically designed experiments the finite-element simulation is verified and subsequently the prediction of the relevant transport mechanisms and hence the optimization of the FAST process parameters is enabled. In particular a sound knowledge of field assisted sintering for arbitrary electrically conducting materials is gained.On the basis of the expected results of the project, for the first time a comprehensive description of the densification process occurring during FAST of metallic powder systems - which includes the influence of the material, particle size, surface quality, pressure, temperature and electric regimes - will be given. Transferring the assumptions made for the model systems on to real powder systems enables a more reliable design of the densification and the evolution of the microstructure. Furthermore, the scientifically sound description of the FAST process shall replace guesses not supported neither by numerical nor experimental evidence.