Spark Plasma Sintering of Monolithic Silicon Carbide and Silicon Carbide-Graphene Composite

Abstract

Ball milled α - SiC (2.73 μm) was consolidated rapidly using spark plasma sintering at 1800, 1900, and 2000 ̊C under 90 MPa pressure and 20 min of soaking time. Relatively high densification (>90% relative density) was achieved at 2000 ̊C. The densification stages were identified, and a three stage densification process was proposed. The formal densification study was performed using the model proposed by Ashby, and the dominant mechanism for densification was determined to be grain boundary accommodated diffusion controlled creep. The formal grain growth mechanism was also investigated, and similar result was found. The value of stress exponent was calculated as 1.1, and the activation energy needed for final stage densification was found to be ≈ 427 - 500 KJ/mol. Also, nano-grain clustering was identified as an auxiliary mechanism from microstructural analysis.The reinforcement of SiC was done with 1, 2, and 3 vol.% graphene. Mechanical characterizations were performed on the reinforced ceramics, and inter-granular fracture was seen. Graphene didn't cause any improvement in hardness of SiC, but showed substantial improvement in flexural strength. Graphene proved to be very useful in restraining grain growth, but decreased the density of monolithic SiC.