Tribological Behavior Of N31 Phosphatelaser Glass In Dry Air And Liquid Water

Nd-doped phosphate laser glass is an ideal gain medium for high-peak-power solid-state lasers because of its higher storage capacity for optical energy, which has therefore been widely used in high-peak-power solid-state laser systems “National Ignition Facility” manufactured in USA and “Shenguang” manufactured in China. Some optical machining methods, such as grinding, abrading and polishing, are used to obtain ideal surface of phosphate laser glass, the essence of these machining processes are the material removal/wear occurred between abrasive and glass surface under shear abrasion. However, due to the polishing solution and the cooling liquid environment, water molecules in the liquid would inevitably affect these machining processes, which further affect the material removal.In this paper, the material removal regularity and damage characteristics of phosphate laser glass against silica ball wear contrastively investigated in dry air and liquid water under various loads through some straight line reciprocating friction and wear tests. First, the friction and wear behavior of phosphate laser glass against high silica content of silicate glass ball were studied in the atmospheric environment under various load. Subsequently, the material removal regularity and damage characteristics induced by water in phosphate glass/silica ball pairs were researched. Eventually, the wear mechanism of phosphate laser glass in dry air and liquid water was discussed, and the tribochemical reaction in the wear of phosphate laser glass/silica ball pairs in liquid water was discussed emphatically. Based on the above systemic investigation, the main conclusions can be summarized as following:(1) Load is one of the most significant factors which changed the way of material removal during the friction and wear processes of phosphate laser glass in the atmospheric environment. With the increase of load, the friction coefficient of stable wear stage decreased gradually, and the wear volume of phosphate laser glass first increased sharply and then slowly. The wear mechanism transition from abrasive wear to the combined action of abrasive wear and crack initiation, and finally to material brittle exfoliation was observed by increasing the load. The tribochemical reaction is not obvious in the wear tracks in phosphate laser glass. This study provides a reference for the subsequent tests which performed in dry air and liquid water conditions.(2) The stress corrosion can not assist the material removal of phosphate glass. The wear depth and volume of phosphate glass is larger in dry air than that in liquid water, especially in relatively higher normal load. It indicates that the liquid water can not accelerate the wear of phosphate glass against silica ball, on the contrary, it will prevent the wear of phosphate glass in water.(3) In liquid water, the wear of phosphate laser glass/silica ball pairs is the combined results of the mechanical interaction and tribochemical reaction. Due to the ion exchange of the hydration reaction and structure damaged of hydrolysis reaction of phosphate laser glass in liquid water, some alkali metal cations will be leached in liquid, and these cations will further react with the production of silica and water. The tribochemical reaction production of water, silica and phosphate glass have a soft gel-like property, and they will adhere to the friction interface to prevent the wear of phosphate glass and play a lubrication role in the wear process in water.