Tribological Behavior Of Phosphate Laser Glass Under Various Humidity Conditions

Nd-doped phosphate laser glass has been widely applied for high-peak-power laser system as an ideal gain medium all over the world,because of its superior optical property. However, the ultra-high surface quality with ultra-smooth and low-defect is required for its application. Generally,surface planarization of phosphate laser glass is accomplished by the magnetorheological finishing, where the material removal is achieved by the shear abrasion between the abrasive particle and the surface of the glass. Due to the polishing process is usually exposed into the water environment, the water molecules will be involved in the processing, thus it is of importance to understand the role of water on the material removal of phosphate laser glass surface.In this thesis, the silica glass ball was selected as the counter-surface, while the relative humidity was set as 55% ~ 60%, then the effect of water on the material removal behavior of phosphate laser glass materials was systemically studied. Based on these results, the friction and wear behavior of phosphate laser glass were investigated unders various humidty conditions; Eventually, according to the Raman and Nano-indentation results, the wear mechanism of phosphate laser glass were analyzed when gaseous water is involved. Based on the above investigation, the main conclusions can be summarized as following:(1) It was found that under the same contact load condition, the wear depth and volume of the phosphate laser glass in the humid air is much lower than that in dry air, while the wear depth and volume of the silica glass ball in the humid air are much higher than that of the dry air. These results suggest that water-induced stress corrosion can not accelerate the material removal of phosphate laser glass surface, but it can accelerate the material removal of silica glass ball.(2) The wear of the phosphate laser glass was decreased as the humidity increased. When rubbing against alumina and zirconia ceramic ball, it can be also found that the wear of phosphate glass decreased when gaseous water is involved.Based on the analysis results, it was believed that the superior wear resistance ofphosphate glass surface in humid air must be the consequence of tribochemical reactions occured in glass interface, the adhesive wear debris of the surface, and strengthening mechanical properties of the glass surface, and the tribochemical reactions may play a predominate role.(3) It was also deduced that the tribochemicall reactions during the wear of phosphate glass in humid condition was due to water molecules in the humid air can be adsorbed at the surface of glass. As a result, a hydration layer can be formed at glass surface. During the wear process, the stress-induced hydrolysis reaction can make the long chain of phosphate network depolymerized to short chain, and these phosphate short chains of phosphate glass network will exist at the glass surface, and participate the shear abrasion at the surface of the glass. As a result, so as to the wear of phosphate glass was suppressed compared to that in dry air.