19th meeting of the FAST/SPS expert group held successfully

The 19th meeting of the expert committee "Field Assisted Sintering Technique/Spark Plasma Sintering" (chaired by Prof. Olivier Guillon, Forschungszentrum Jülich) took place on December 01st, 2021. The meeting was held at Atelier Auer, Mercedesstr. 3, Stuttgart. Afterwards, there was a possibility to visit Dr. Fritsch in Stuttgart-Fellbach. About 40 national and international participants from industry, research institutes and universities actively participated in the meeting.

There were 8 presentations, which are shortly summarized:

1) Introduction of Dr. Fritsch GmbH (Jens Huber, Dr. Fritsch GmbH)

The company Dr. Fritsch was founded in 1953 and moved to Stuttgart Fellbach in 1969. It is family owned, has around 100 employees and two additional subsidiaries in Bangalore, India and Danyang, China. Portfolio of Dr. Fritsch contains FAST/SPS devices (more than 1000 are operated in industry, amongst others for diamond reinforced materials), as well as devices for dosing, mixing, granulating and cold pressing. A special focus lies on automation of FAST/SPS related processing steps. Furthermore, Dr. Fritsch delivers powders for diamond reinforced materials.

2) Machine science – transformer technique (Gerhard Weber, Dr. Fritsch GmbH)

Gerhard Weber explained the different possibilities to design a FAST/SPS device with a special focus on the transformer. In general, it is targeted to improve efficiency of the cycle time and energy consumption by optimizing the mould set-up and the electrical conditions of the process. 4 concepts of resistance heating are usual in FAST/SPS technology i.) AC with two phases ii.) DC with 3 phases iii.) AC with 3 phases (P+) iv.) pulsed DC – 3 phases. All concepts were discussed with respect to energy efficiency and robustness. Furthermore, the importance of mould design and resistance of mould materials were introduced.

3) Powder material: Preparation for SPS sintering (Christian Weiss, Dr. Fritsch GmbH)

Dr. Fritsch distributes materials and develops related processes for diamond reinforced materials ranging from raw materials, ready to use powder mixtures, customized mixtures, industrial diamonds, cubic BN, granules, pressing and release agents, binder for granulation, “alloys” by high energy milling and related comprehensive technical support. It was discussed how particle size influences further processing and properties.

4) Industrial production of honing tools using FAST/SPS (Klaus Fleckenstein, DIATO GmbH + Co. KG)

DIATO GmbH + Co. KG manufactures tools for honing of high performing parts, which are applied e.g. in power trains, defence, aerospace and heavy duty vehicles. The wear resistant part of the tools (mostly bar shaped, diamond reinforced parts) is made by FAST/SPS in graphite tools. Honing is often the last manufacturing step of complex parts, so it requires high quality tools and quality assurance. Due to high demands of homogeneously filling related cavities in the FAST/SPS moulds and large number of powder compositions, automation of the FAST/SPS step is still low.

5) Discrete element model of powder sintering and its extension to the SPS/FAST process (Prof. Jerzy Rojek, Polish Academy of Science, Warsaw)

Jerzy Rojek introduced the general principles of discrete element model (DEM) of powder sintering processes including i.) sintering mechanisms at microscopic level ii.) formulation of the DEM sintering model and iii.) simulation of a sintering process as an example. Then he explained how to transfer this model to develop DEM for FAST/SPS, giving basic assumptions and then presenting DEM simulation of the electrical current flow through a granular material.

6) Segregation controlled densification and grain growth during FAST/SPS of Y2O3 ceramics (Dr. Moritz Kindelmann, Forschungszentrum Jülich GmbH)

Cation doping of Y2O3 is an established approach for tailoring densification and grain growth during the sintering of ceramic materials. Doping with two isovalent dopants (La3+ and Gd3+) was investigated with respect to densification behavior and grain growth. Structure and chemistry at the grain boundaries was observed by aberration corrected TEM.

7) Examples of densification of multimaterials using FAST/SPS (Dr. Erich Neubauer, RHP-Technology GmbH)

At RHP-Technology, several devices for pressure and field assisted sintering are operated: i.) conventional hot pressing ii.) FAST/SPS iii.) Electro sinter forging/rapid sinter pressing in preheated tools. Erich Neubauer gave an overview about current topics of research and application of these technologies comprehending recycling of Si from photovoltaics, bonding of materials with large difference in physical properties, fiber reinforced materials, ceramic- refractory metal composites, Cu-Ag composites and tiger metals (Au – Ti/Ag composites) for jewelry.

8) Introduction of new member: Materials Research Institute Aalen – Batteries and more (Dr. Stefan Kreißl, Hochschule Aalen)

Stefan Kreißl introduced the Materials Research Institute Aalen and announced that there will be activities in the field of FAST/SPS of battery materials.

Prof. Olivier Guillon closed the meeting discussing some topics of common interest and announced the 10th anniversary of the expert group meetings to be celebrated on 15th – 17th May 2022 in Erfurt as a two day conference.

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