Performance Research On Two-Step Ion Exchange Enhanced Ultra-Thin High-Alumina Silicate Glass

With the popularization of smart phones,smart artificial wear products and ultra-thin liquid crystal displays,the cover glass of these electronic products has also developed toward the direction of ultra-thin,lightweight,and high-strength.Among the common glass materials,aluminosilicate glass becomes the preferred choice for tempered glass panels due to its high hardness,high strength,good mechanical properties,and excellent optical performance.Corning ultra-thin high-alumina silicate glass were treated through three different two-step ion exchange process,and the bending strength（σb）,microhardness（Hv）,surface stress,combining mechanical properties test methods such as CS,DOL and impact strength with EDS microscopic test methods.Two-step ion exchange molten salt formulations and exchange process systems were systematically studied,and one-step ion exchange and two-step comparison of the effect of ion exchange enhancement was compared.Finally,the the structural characteristics of the composite stress-layer glass and the effect of K⁺ion migration on the surface often the enhancement of chemical was discussed.The results indicate:（1）Two-step ion exchange under pure potassium nitrate molten salt conditions.The two-step ion exchange-strengthened high-alumina silicate glass has a bending strength of 746.3MPa and a microhardness of 877.3Hv,which has a certain increase relative to 699.8MPa and 831.7Hv of the one-step ion-exchanged glass.The stability of the mechanical properties of the high-alumina silicate glass after the two-step ion exchange has been significantly improved,the surface stress of the glass is low in dispersion,and the distribution uniformity is good.（2）Two-step ion exchange under sodium and potassium mixed molten salt conditions.Through the exploration of different proportions of molten salt formulations,it was determined that the one-step of ion exchange was performed using a sodium-potassium mixed molten salt with a mass ratio（wt%）of Na NO₃:KNO₃=3:7 for tempering,followed by pure potassium nitrate molten salt for the second step ion exchange treatment.The flexural strength of the glass after tempering reached 925.3MPa and 875.1Hv,which was significantly improved with respect to the mechanical properties of the two-step ion-exchanged glass under pure potassium nitrate molten salt.Through the EDS test can be found that the glass surface stress layer curve has a special distribution,the highest peak of K⁺concentration shifts the maximum stress value of the glass to increase the impact resistance of the glass,reducing the internal tensile stress value of the glass and enhance the safety factor of tempered glass.（3）Effect of high temperature heat treatment on the depth of stress layer in the middle zone.In the case of using pure potassium nitrate molten salt,adding a certain period of high temperature heat preservation process between the first step of ion exchange and the second step of ion exchange.Finally,it found that the glass passes the two-step ion exchange process under the condition of a heat preservation system of 520℃/2h,the depth of the surface stress layer reached58.1μm,which is 32μm higher than that of the pure potassium nitrate two-step ion exchange glass surface stress layer without high temperature heat preservation process.The result shows that K⁺can move to the inside of the glass surface along the concentration gradient under high temperature conditions,and“ion migration phenomenon”occurs,thereby increasing the depth of the stress layer of the glass surface and making the glass impact resistance and mechanical stability.