Differences in surface failure modes of soda lime silica glass under normal indentation versus tangential shear: A comparative study on Na⁺/K⁺‐ion exchange effects

Abstract

The effects of exchanging Na+ with K+ on the mechanical and mechanochemical properties of a soda lime silica (SLS) glass were investigated. It is known that replacing smaller modifier ions with bigger ions in the silicate glass network, at temperatures below the glass transition (Tg), produces a compressive stress in the subsurface region that enhances resistance to mechanical damages. This study found that when Na+ ions in SLS are exchanged with K+ ions at 400°C, the hardness, indentation fracture toughness, and crack initiation load of the surface are increased, which is consistent with the chemical strengthening effect. However, the resistance to mechanochemical wear in a near‐saturation humidity condition (relative humidity RH = 90%) is deteriorated. When K+ ions are exchanged back with Na+ ions at 350°C, the wear resistance in high humidity conditions is recovered. These results indicate that the improvement of mechanical properties under indentation normal to the surface is irrelevant with the resistance to mechanochemical wear under tangential shear at the surface. Based on the analysis of the surface chemical composition, silicate network structure, and hydrogen‐bonding interactions of hydrous species in the subsurface region, it is proposed that the leachable Na+ associated with non‐bridging oxygen and subsurface hydrous species in the silicate network play more important roles in the mechanochemical wear of SLS at high RH.

Effects of tempering and heat strengthening on hardness, indentation fracture resistance, and wear of soda lime float glass

“…Previous studies have shown that the ν Si‐O, as red‐shift after chemical tempering (K + ion‐exchanged SLS) is due to an increase in the Si‐O bond length, but that the wear resistance deceases for such glasses . This supports the hypothesis that strained bonds may influence the mechanochemical reactions occurring at high humidity and decrease the wear resistance of the glass.…”

“…The HS process is not as controlled as the TT process and often results in asymmetric residual stress patterns . Previous works using a ball‐on‐flat tribometer showed peculiar wear behaviors of the SLS glass as a function of relative humidity (RH) of the testing environment . In dry conditions (0% RH), the materials harder than SLS mechanically abrade and scratch the glass surface which is in accordance with the Reye‐Archard‐Khrushchov wear criterion .…”

“…Also, previous studies have shown that wear resistance (mechanochemical response) could not be assumed to correlate with hardness (mechanical response). For instance, although K + ‐exchanged SLS glass has a higher hardness than SLS, it is less wear resistant at high humidity …”

“…Previous studies attributed SLS wear resistance to the presence of leachable sodium ions . It has been demonstrated that sodium in glasses with higher fictive temperatures has a greater susceptibility to leaching due to a larger free volume .…”

Surface damage resistance and yielding of chemically strengthened silicate glasses: From normal indentation to scratch loading

“…11 Such understanding is often generated by examining the initiation of well-defined defects, for example, generated using sharp Vickers or Berkovich indenter tips 3 or wedges. 12,13 Also on chemically strengthened glasses, indentation deformation and cracking, 8,[14][15][16][17][18][19][20][21] scratch resistance, [21][22][23][24] abrasive wear, 20 and the response to impact load 16,17,25,26 were extensively studied over the past years. However, sharp contact experiments such as underlying most of these studies represent rather harsh conditions, with local stress easily approaching the range of 10 GPa.…”