Tougher Ceramics in Solid Solution

Significance 

Recently, carbonitrides are used in numerous applications such as lithium-ion batteries, heat conductors and soft magnetic materials owing to their excellent physical, mechanical and chemical properties. Consequently, it is easy to control the above-mentioned properties by controlling nitrogen and carbon concentrations thus attracting significant attention of researchers. Among the available carbonitrides, silicon carbonitrides is widely preferred. Presently, several methods for preparing silicon carbonitrides like pyrolysis, physical and chemical vapor deposition have been developed. Unfortunately, these methods result in the production of amorphous silicon carbonitrides that further crystallize to form nanocomposites with limited applications due to their high-density grain and phase boundaries. Alternatively, recent studies showed that despite the potential of using low-density ß-SiN4 as a promising solution, some of their properties such as low thermal expansion coefficient still impede their acceptance. Therefore, researchers have been looking for effective alternatives and have identified silicon carbonitrides as a promising solution.

Jiangsu University researchers led by Associate Professor Guomin Hua from School of Materials Science and Engineering in collaboration with Professor Yang Qi at Northeastern University investigated the influence of carbon concentration on the mechanical property, stability lattice dynamics and electronic structure of silicon carbonitrides base on the first principles calculations. Particularly, they purposed to examine the feasibility of utilizing silicon carbonitride in fabricating high-speed ceramic bearings. Their work is currently published in the research journal, Journal of The American Ceramic Society.

Briefly, the research team cross-examined the solubility of carbon in silicon carbonitride. Next, ß-Si3(Cx,N1-x)4 was fabricated due to its potential for use as high temperature and high-speed applications. The research team also investigated the influence of carbon concentration on different properties of silicon carbonitride solid solution. Eventually, the obtained results were compared to those obtained through first principles calculations.

The authors observed that the solubility of carbon in ß-Si3(Cx,N1-x)4 was recorded at approximately 15%. Consequently, within the allowable solubility limits, increase in carbon concentration resulted in a corresponding decrease in density and Young’s modulus and an increase in the Poison’s ratio of the material. However, carbon concentration could be modified to optimize the ductility and fracture toughness properties attributed to the formation of metallic bonds. In addition, it was worth noting that two criteria were responsible for controlling the structural stability of the silicon carbonitride, that is, elastic stability for a stressed state and energy stability criteria for an unstressed state.

In summary, the study by Guomin Hua and colleagues successfully investigated the influence of carbon on the dynamics and properties of silicon carbonitride. To actualize their study, the solid solutions of ß-Si3(Cx,N1-x)4 was prepared through self-propagating high-temperature synthesis and its contribution to enhancing the ceramic toughening and phase transition evaluated. Due to the excellent results, ß-Si3(Cx,N1-x)4 solid solution will pave way for the fabrication of high-speed ceramic bearings with applications in numerous fields.

In our recent work, we try to emphasize that role of solid solution in the ceramic toughening, because it is different from the traditional toughening mechanism of ceramics, such as transformation toughening or crack bridging” said Guomin Hua, first author in a statement to Advances in Engineering.

Reference

Hua, G., Zhong, J., Qi, Y., & Cheng, X. (2018). Influence of carbon on stability, mechanical property, electronic structure, and lattice dynamics of silicon carbonitride. Journal of The American Ceramic Society, 101(12), 5717-5731.

Go To Journal of The American Ceramic Society

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