Investigation of various charge stabilizers on the synthesis and characterization of SiAlON ceramics

Abstract

SiAlON ceramics stabilized with various charge stabilizers having diversified thermal and mechanical properties are utilized for products requiring high contact resistance such as bearings, cutting tools, and automotive brake pads. Oxygen rich SiAlON ceramics doped with various nano-sized metal oxide (MO) stabilizers were synthesised. The nanosized starting powder precursors comprising Si3N4, AlN, Al2O3, and SiO2 along with oxides of Ba, Y, Mg, La, Nd, Eu, Dy, Er, and Yb as the MO charge stabilizer were employed in developing different SiAlON samples. The initial powder precursors were homogenised using an ultrasonic probe sonication method, and the samples were then exposed to spark plasma sintering at 1500 ℃ for 30 minutes under 50 MPa pressure. According to the generic alpha SiAlON formula: Mm/vSi12-(m+n)Al(m+n)OnN16-n, the m and n values of the sample compositions employed in this investigation are 1.1 and 1.6, respectively. The synthesised samples' physical properties, microstructure and crystal structure evolution, and thermo-mechanical characteristics were investigated. The produced ceramics were studied with electron microscopy and X-ray diffraction to better understand and relate structural properties to densification, hardness, thermal conductivity, and fracture toughness. Full-densified ceramics with relative densities of 97–99 percent were created because of the SPS localised heating and the greater reactivity of the nanosized particles. Vickers hardness values were observed to vary from 12.4 to 17.0 GPa, with the particle size of the alpha SiAlON (primary) phase having a substantial impact. The samples had a fracture toughness of 4.1–6.2 𝑀𝑃𝑎. 𝑚1/2 , according to the tests. SiAlON samples synthesised using Er and Yb charge stabilisers had the largest content of the long beta phase (5.7 and 6.2 𝑀𝑃𝑎. 𝑚1/2 , respectively) to attain their highest fracture toughness values. It was concluded that scientifically selected metal oxide charge stabilizers are beneficial in developing SiAlON ceramics with properties tailored according to specific applications at lower sintering temperature of 1500 ℃.