Research On Surface/Subsurface Damage Of Glass-Ceramics Induced By Ultra-precision Grinding

Glass-ceramics is a polycrystalline brittle material consisting of glass phase and crystalline phase. Glass-ceramics with low thermal expansion coefficient is widely used in aerospace industry, defense industry and other fields, owing to its good physical properties, excellent mechanical property and favorable chemical stability, especially for its extraordinary low thermal expansion coefficient. As an important processing method for brittle materials, grinding inevitably induces the surface and subsurface damage. The surface and subsurface damage will reduce the strength of the glass-ceramics components and the long term stability, affect the image quality, and finally reduce the service life of the optical element. In consequence, that efficiently machining glass-ceramics with low surface and subsurface damage has become the focus of the glass-ceramics machining.In this study, the surface topography, surface and subsurface damage characteristics and material removal mechanism of glass-ceramics ground by diamond wheels with different abrasive sizes of #500,#1500,#2000 and #5000 are investigated. The relationship between the subsurface damage depth and surface roughness of ground glass-ceramics is also established. Main research content of this study is as following:(1) Glass-ceramics were ground by diamond wheels with different abrasive sizes of #500,#1500,#2000 and #5000, and the surface topography, surface roughness, and surface damage characteristics of ground glass-ceramics were investigated. With the decrease of abrasive sizes of the diamond wheels, the surface of the glass-ceramics became more and more smooth, the surface roughness of the glass-ceramics decreased, and the surface damage form transforms from pits and microcracks which caused by brittle fracture to micro-scratches which caused by plastic flow of glass-ceramics gradually.(2) To investigate the subsurface damage of the glass-ceramics ground by diamond wheels with different abrasive sizes, many detection methods including cross-section microscopic observation method, angle cross-section microscopic observation method and transmission electron microscopy were taken. With the decrease of abrasive sizes of the diamond wheels, the subsurface damage depth of the glass-ceramics decreased, and the subsurface damage form transforms from microcracks in the subsurface layer to plastic flow of glass-ceramics closing to the material grinding surface. With the decrease of abrasive sizes of the diamond wheels, glass-ceramics removed in brittle-mode grinding changed to removed in ductile-mode grinding.(3) Based on the related theory of indentation fracture mechanics, the relationship between the subsurface damage depth and surface roughness of ground glass-ceramics was established when the subsurface damage was microcracks. To verify the correctness of the relationship, glass-ceramics was ground by #500 diamond wheel with different feed rates and the subsurface damage depth and surface roughness of the ground glass-ceramics were measured.