Producing high performace porous materials by Pulsed Electric Current Sintering
Homogeneity in sintering of fine Ni-20Cr powder by PECS process
Pulsed Electric Current Sintering (PECS), also known as spark plasma sintering (SPS) or plasma activation sintering (PAS) is technique used for densifying power compacts or materials such as metals and ceramics and combination thereof. The attractive features of the process are that it allows compaction and sintering in a single stage and the process itself is quite rapid.
PECS also shows promise in being able to produce high performance porous materials. The difficulty in producing such porous materials is the ability to produce a homogenous microstructure.
In this paper, Japanese researchers, Manabu Sato, Makoto Nanko, Koji Matsumaru and Kozo Ishizaki, from the Nagaoka University of Technology examine density homogeneity in partially–sintered metallic bodies produced using PECS. In order to obtain homogeneous microstructure the effects of geometry of the graphite die is also investigated. Fine Ni-20Cr powder with particle size of 5 µm and coarse powder with 70 µm in particle size were used in order to discuss effects of powder size.
The researchers successfully produced porous bodies using the PECS technology. They found that sintering rates were faster for finer starting powders when compared to coarser powders, with differing dies sizes and geometries making no significant difference. Coarser powders, despite their slower rates of densification produced homogenous microstructures. Finer powders in contrast, were found to be significantly denser on the inside compared to the outside. This was attributed to temperature gradients from Joule heating and heat transfer during the sintering process. The use of die with thicker walls was found to resolve this issue and at the same time improved reproducibility.