Hot pressed Si3N4 ceramics using MgO–Al<sub>2</sub>O<sub>3</sub> as sintering additive for vehicles engine parts

Abstract

In an attempt to optimize a qualified ceramic material with enhanced and outstanding characteristics, the current work aims to study the processing of dense Si 3 N 4 based ceramic composites by hot pressing method. The proposed material consists of an equimolecular mixture of α and β-Si 3 N 4 with adding of variant amounts of MgO‒Al 2 O 3 spinel as sintering additive. Investigation of the different characteristics of the obtained ceramics with respect to densification parameters, hardness, fracture toughness, bending strength and cold crushing strength was performed and correlated to their microstructure behavior. Results indicated that dense well distributed structure of silicon nitride ceramics was attained by adding of variant amounts of the magnesium aluminate spinel structure. Moreover, insertion of MgO‒ Al 2 O 3 mixtures to Si 3 N 4 ceramics was established to enhance their grains growth demeanor, increased the elongated β-Si 3 N 4 grains and their aspect ratio. Furthermore, it was revealed that, increasing MgO ratio relative to Al 2 O 3 one in the spinel structure was responsible for enhancing the different properties of the produced nitride ceramics. Results suggested that the obtained hot pressed Si 3 N 4 ceramics seeded with β-Si 3 N 4 particles can be a successful candidate in automotive industry as alternative parts for the vehicle engines.