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

• Applicants: Professor Dr.-Ing. Bernd Kieback; Professor Dr.-Ing. Thomas Wallmersperger
• Subject Area: Glass, Ceramics and Derived Composites
• Term: from 2014 to 2020
• Project identifier: Deutsche Forschungsgemeinschaft (DFG) - Project number 262396337

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.

• DFG Programme: Research Grants