Committee Members: 

Dr. Robert Speyer, Advisor, MSE

Dr. Rosario Gerhart, MSE

Dr. Naresh Thadhani, MSE

Dr. Arun Gokhale, MSE

Dr. Richard Neu, ME

SINTERING METHODOLOGIES FOR SILICON CARBIDE CERAMICS

ABSTRACT: Silicon carbide (SiC) ceramics are known for their outstanding properties like high hardness, low density, high strength, high oxidation resistance, high thermal shock resistance, low high-temperature creep, and chemical inertness. This makes SiC a leading candidate for a wide range of commercial applications. Sintering of SiC can be divided into solid-state sintering and liquid-phase sintering. Coventional solid-state sintering of silicon carbide includes using boron/boron carbide and carbon as sintering aids. Liquid-phase sintering of silicon carbide has shown great potential to prepare highly densified SiC while sintering at relatively lower temperatures. To better understand the mechanism of solid-state sintering of SiC, this proposal has investigated how varying amounts of B4C and C affects the relative densities, microstructures and mechanical properties of SiC. The results has shown that the critical amount of B4C needed is around 0.26 wt%, which is related to the solubility of B4C in SiC. The Vickers hardness and Vickers indentation fracture toughness (VIF) of SiC with varying B4C and C are 23.69-25.83 MPa· m1/2 and 3.18-3.85 GPa, respectively. To investigate the liquid-phase sintering methodologies of silicon carbide, different atmospheres and powder beds have been used. The results show that different sintering temperatures are required for different atmospheres, with nitrogen requiring the highest sintering temperature (1950°C), and helium requiring the lowest (1700°C). The objective

of this study is to investigate the transition between solid-state sintering and liquid-phase sintering and its potential merits. An additive combination of AlN and Y2O3 has been selected. AlN on its own is known to form a solid solution with SiC, while in combination with Y2O3, forms a eutectic liquid phase. By varying the amounts of AlN and Y2O3, a study on its effect on the relative densities, microstructures, and mechanical densities will be conducted. This research will also construct a 2-D computer model of sintering using MATLAB. The green microstructure will be constructed with random number generator and a fall-and-roll algorithm. The movement of atoms will be based on prejudices representing thermodynamic favorability.