Microstructural variations and machining characteristics of silicon nitride ceramics from increasing the temperature in laser assisted machining

Abstract

Industrial ceramics is one of the new materials that have advantages like high strength characteristics, wear-resistance, chemical stability and corrosion-resistance. In general, the production of high strength ceramic requires finishing processes because of the sintering processes, but the machining of ceramic is difficult due to its high strength and brittleness. If such disadvantages are complemented, the engineering ceramics will probably be applied in more diverse fields. Therefore, as a way to overcome such weaknesses, laser assisted machining that locally heats, softens and cuts materials was studied intensely by using laser beams as a heat source. In this paper, material changes by difference of a laser power and the structural changes of the material surface when it was heated by laser beam were observed. When the temperature increased, the Si and N which are comprised the silicon nitride decomposed and turned to gas, eventually erupting outside or forming porosity inside to induce micro-cracks. In addition, as YSiAlON, which surrounded β-Si₃N₄, softened at 1,000°C or above, cutting was enable due to plastic deformation. In particular, the surface of the specimen oxidized at a high temperature formed an amorphous silicate, and subsequently experienced deterioration of hardness compared to silicon nitride.