Mechanical properties of chromium–chromium sulfide cermets fabricated by self-propagating high-temperature synthesis

Metal sulfides are widely used in a variety of applications requiring high hardness and toughness. In this study, the microstructure and mechanical properties of chromium–chromium sulfide cermets are investigated. The chromium–chromium sulfide cermet was manufactured using self-propagating high-temperature synthesis, a process where the material is created under a self-sustaining combustion reaction between the chromium and sulfur. This type of synthesis allows the creation of near-net shape structures and offers the possibility of tuning material properties and material behavior by changing the composition of the reactant. Microstructural characterization was performed using optical microscopy, scanning electron microscopy, and energy dispersive spectroscopy. The mechanical properties of the cermet (Young’s modulus, fracture toughness, flexural strength, and microhardness) have been measured and related to morphology and chemical composition of the samples. Results show that dense cermets (about 7 % porosity) with specific structure have been obtained. Pure CrS has a significant hardness, but its toughness was insufficient for tool applications. However, we found that the density and fracture toughness of the cermets increase with the addition of Cr. The addition of Cr also improved the flexural strength and hardness of the cermet by 60 % and almost 38 %, respectively. Introduction Engineering ceramics are attractive materials because of their low density, high compressive strength, and hardness. However, their use in actual applications is currently limited by their brittleness, fragility, and poor toughness. A possible approach to toughen ceramics is the inclusion of a metallic ductile phase. Such ceramic–metal compounds, called cermets, combine the hardness and stiffness of ceramics with the toughness and ductility of metals [1–5]. Among cermets, metal sulfide composites are in high demand in the chemical, metallurgical, and electrical industries because of their valuable characteristics such as hardness, semi-conductivity, electroluminescence, infrared transparency, catalytic, and magnetic properties [6–9]. Currently, metal sulfides are used for cathodes in batteries, additives in steel production, high-temperature lubricants, catalytic material for hydro-desulfurization, electrodes for hydrogen fuel cells, and solar energy conversion into electric and chemical energy [7, 10–16]. There is currently no bulk production of chromium sulfide, however, we know from the literature that chromium sulfide has magnetic properties, and already is used as a catalyst in chemical processes, and as a solid lubricant [7, 17–19]. Metalsulfur compositions, such as CrS are attractive in that they offer the possibility of fabrication using the selfpropagating high-temperature synthesis (SHS) technique. In a previous study, we used a new method for the preparation of the metal-sulfur precursor charge based on the ability to melt-cast the precursor mixture [20]. We used SHS to produce a chromium–chromium sulfide cermet, using the ability of the metal–sulfur mixture to support the propagation of reactive waves. This ability, with the properties of the reaction products (i.e., low gas evolution Electronic supplementary material The online version of this article (doi:10.1007/s10853-015-8902-7) contains supplementary material, which is available to authorized users. A. Nabavi S. Goroshin D. L. Frost (&) F. Barthelat (&) Department of Mechanical Engineering, McGill University, 817 Sherbrook Street West, Montreal, QC H3A 0C3, Canada e-mail: [email protected] F. Barthelat e-mail: [email protected] 123 J Mater Sci (2015) 50:3434–3446 DOI 10.1007/s10853-015-8902-7