Effect of water on wear of phosphate laser glass and BK7 glass

Using a reciprocating ball-on-flat tribometer, the friction and wear behaviors of phosphate laser (PL) glass and BK7 borosilicate glass were investigated by rubbing against Al2O3 ball in dry air and liquid water to reveal the effect of water on the wear of the two glasses. In dry air, the wear of PL glass and BK7 glass shows a typical characteristic of mechanical wear. The damage of PL glass dominates by the formation and extension of Hertzian crack, and the damage of BK7 glass dominates by exfoliation-in-chips and three-body abrasive wear. Water affects both the subsurface fracture and material removal for the two glasses. On the one hand, the subsurface fracture is suppressed greatly for both the PL glass and BK7 glass when they are rubbed in water. The lower shear stress caused by water film at friction interface is considered as the main reason of weakened subsurface cracking for the two glasses. On the other hand, compared with dry air, water promotes the material removal of PL glass but reduces the material removal of BK7 glass. It suggests that the material removal of glass in water depends on the combined effect of the chemical stability of glass and the contribution of water lubrication.