Tribo-mechanical characterization of SPS processed, phase pure 15R-SiAlON polytype: Effect of sintering temperature

Abstract

The work reports tribo-mechanical properties of spark plasma sintering processed dense, phase pure 15R-SiAlON polytype in the absence of any external sintering additive. At low sintering temperatures (1600–1700 °C), the polytype was ~ 82–87% dense. On contrary, sintering at 1800–1900 °C under 40 MPa for only 10 min resulted in more than 98% dense material. Microstructure analyses revealed formation of inadequately grown grains at low SPS temperatures that transformed to elongated grains at 1800–1900 °C. Sintering of the 15 R polytype at 1900 °C offered Vickers hardness as high as ~ 21 and ~ 16 GPa at 0.2 and 2 kgf, respectively, presumably due to the well-known grain refining effect achieved through SPS processing. Fracture toughness at 10 kgf of the dense 15R-SiAlON was found to be ~ 4.43 MPa-m0.5. This indicated suitable self-reinforcing effect offered by elongated grains formed in the dense polytype. Indentation size effect of the polytype has been reported. Unlubricated linear scratch experiments under sharp diamond Vickers indenter revealed adequate wear resistance of the dense polytype. Wear rate and friction coefficient were found to be ~ 9.58 × 10−4 mm3/N-m and ~ 0.35, respectively, for the 1900 °C sintered 15R-SiAlON specimen under 20 N. Present tribo-mechanical results of phase pure 15R-SiAlON polytype might be useful for futuristic development of advanced ceramic matrix composites where this particular polytype can play role of a promising reinforcing phase.