Carbon contamination during spark plasma sintering of powder materials: A brief overview

This review aimed to determine and analyze the current understanding of the origins and mechanisms of carbonization in different materials: 1) metallic and hard alloys, 2) oxide, carbide, and nitride ceramics, and 3) transparent ceramics during spark plasma sintering (SPS). The carbon sources include the graphite mold, graphite punches, and graphite foil. These are used to reduce the gap between the sample and the inner surface of the mold. It has been shown that the carbon diffusion can strongly affect the chemical and phase composition, microstructure, and physical and mechanical properties of samples produced using SPS technology. The researchers consider two main mechanisms of carbon interaction with the materials being sintering. The diffusion of carbon into the surface layers of the material is suggested to be the primary mechanism. The characteristic scale of carbon diffusion is tens to hundreds of microns. The carbide layer is often formed on the surface of the material. The second mechanism that promotes the carbon contamination of the samples is suggested to be the condensation of carbon-containing gases, such as CO and/or CO2, inside the pores of the sample. It is proposed that the carbon-containing gases are mainly formed as a result of the interaction between graphite components of the mold and residual oxygen. The presence of CO and/or CO2 gases in the work chamber of the setup is possible during SPS. It has been shown that the addition of carbon can enhance the mechanical and performance properties of structural materials. That opens up new prospects for the fabrication of functionally gradient materials by SPS. At the same time, carbon contamination leads to the deterioration of the dielectric and optical properties of functional ceramics, which necessitates the improvement of the SPS modes.