Design of mechanically advantaged glasses with hydration‐induced stress profiles

Abstract

The glass composition design work leading to the discovery of highly crack resistant glasses exhibiting hydration‐induced stress profiles is described. Initial hydration studies on ternary aluminosilicate glasses show the importance of potassium for facilitating hydration. Further modification of the glass composition through the incorporation of P2O5 increased the hydration rate such that a specimen with a 29‐µm hydration depth was prepared by holding in an 85°C 85% relative humidity chamber for 65 days. Not only did this glass have a high Vickers indentation crack resistance of >20 kgf, but the sample also displayed considerable stored energy at failure. This indication of a stress profile was subsequently measured and a compressive stress (CS) of 400 MPa with a compressive depth of layer of 29 µm was found. The initially long process times were shortened using pressurized steam vessels. When held at 250°C and .3 MPa, samples can be prepared with surface CSs >300 MPa and compressive depths >30 µm in less than 8 h.

On the structure and properties of hydrothermally toughened soda–lime silicate float glass

“…As H 2 O (and H 3 O + ) is larger than Na + this results in an apparent densification of the network detected by the drop in S . These results provide the first clear observation of a reduction of the free volume on the glass surface during HT and are consistent with the build‐up of compressive residual stresses, already spotted in previous works, 27,30,40 that can partially explain the water‐induced toughening (Figure 1).…”

“…A few papers appeared describing the effect of hydrothermal treatments (HT) on increasing the glass resistance on flaw formation after Vickers indentation. 25,26 In the case of specifically designed glasses subjected to HT, the critical load can be as high as 20 kgf 27 (about two orders of magnitude larger than normal SLS). These studies confirmed that the hydrated glass surfaces are more resistant to crack formation.…”

“…Finally, since H 3 O + is larger than Na + it is expected to build up intense compressive stresses (≈2 GPa) close to the surface which prevents crack nucleation. 27,30,40 It is worth noting that this strengthening approach requires more complex equipment than that of the usual K + → Na + ion exchange as it requires a closed vessel sustaining internal pressure (≈18-19 bar at 200 • C). However, it operates at significantly lower temperatures and provides a substantial toughening of the structure which is not achievable with other approaches.…”

“…Note that the structural densification is also expected to relax the indentation stresses providing an additional toughening effect. Finally, since H 3 O + is larger than Na + it is expected to build up intense compressive stresses (≈2 GPa) close to the surface which prevents crack nucleation 27,30,40 . It is worth noting that this strengthening approach requires more complex equipment than that of the usual K + → Na + ion exchange as it requires a closed vessel sustaining internal pressure (≈18–19 bar at 200°C).…”

Surface Hardness and Abrasion Threshold of Chemically Strengthened Soda-Lime Silicate Glasses After Steam Processing

“…For example, it was shown that H 2 O vapor treatments can be used to modify the surface mechanics of various silicate glasses in very short treatment times [29]. Similar to IOX, the incorporation of water into the glass surface is thought to enable the generation of persistent layers of compressive stress [30], [31], while also affecting material plasticity, elastic properties and fracture characteristics [32], [33].…”