Effect of humidity on friction, wear, and plastic deformation during nanoscratch of soda lime silica glass

Physical flaws and defects on glass surfaces are known to reduce the mechanical strength and chemical durability of glass. The formation of surface defects depends not only on the mechanical conditions of the physical contact but also on the environment in which the contact is made. In this study, the nanoscratch behavior of soda lime silica (SLS) glass was investigated in 10% and 60% relative humidity (RH) conditions. Based on the evolution of friction and scratch depth, the deformation of SLS glass surface could be divided into four regimes: elastic deformation and recovery (E), RH-independent mild plastic deformation (P-1), RH-dependent intermediate plastic deformation (P-2), and RH-independent severe plastic formation (P-3). It is quite surprising to observe that plastic deformation of the glass surface has dependence on RH of the environment (outside the glass) because plastic deformation is the process occurring below the surface (inside the glass) by the externally applied load. From this result, it can be inferred that frictional energy dissipation mode at the sliding interface, which is a function of adsorbed water molecules, influences the subsurface deformation mode. Although friction, wear, and subsurface deformation/damage are all coupled, there is no direct one-on-one correlation among them.