Research On Preparation And Chemical Strengthening Of Li₂O-Al₂O₃-SiO₂ Glass-Ceramics

Lithium-aluminum-silicon-based glass-ceramics is a glass-ceramic material with excellent optical and mechanical properties and low thermal expansion coefficient.At present,lithium-aluminum-silicon-based glass-ceramics have been used in many fields,especially as cover materials for touch terminals such as mobile phones,and have been widely used and show great potential for development.Statistics show that,on average,each mobile phone is dropped 7 times a year,which requires the glass cover of the mobile phone to have high mechanical properties.Although lithium aluminum silicon glass ceramics has excellent mechanical properties(hardness600～700Hv,bending strength 100～250MPa and fracture toughness 1～1.5MPam^1/2),in order to further improve the mechanical properties of lithium aluminum silicon glass ceramics,It may also need to be chemically strengthened after crystallization.Therefore,it is of great practical significance to study and prepare lithium-aluminum-silicon-based transparent glass-ceramics for mobile phone covers with excellent mechanical properties.In the experiment,Li₂O,Al₂O₃ and Si O₂ were used as the main raw materials,and the two-step integral crystallization method and the two-step chemical tempering process were used to prepare lithium aluminum silicon-based transparent glass ceramics.The results of the study are as follows:（1）By comprehensively comparing the crystallization and mechanical properties of lithium aluminum silicon transparent glass ceramics with a Mg O content of 0～3wt.%,when the Mg O content increases from 0wt.%to 3wt.%,the crystallization temperature of the base glass decreases from 771℃to At 729℃,the crystallization ability is enhanced;the crystallinity of glass-ceramics increases from 62%to 72%,and the crystal grain size increases from 29nm to 33nm.With the increase of Mg O content,β-quartz solid solution will be precipitated in the glass-ceramic,and the bending strength will increase.（2）Determine the optimal addition amount of Mg O in the glass composition as 2wt.%,optimize the crystallization treatment for the sample（M2）with the Mg O content of 2wt.%,and determine the optimal heat treatment process parameter as:535℃nucleation 4h,635Crystallize at℃for 5h.At this time,the corresponding crystal grain size of the glass-ceramic is 32nm,and the crystallinity is 72%.The microstructure is dense,and the crystal phases are dominated by permeable feldspar and lithium disilicate.The tested Vickers hardness is 673HV,and the bending strength is 213MPa.（3）With the increase of crystallization temperature and the extension of time,the glass-ceramics successively precipitate lithium metasilicate,lithosene feldspar,lithium disilicate andβ-quartz solid solution;the corresponding Vickers hardness increases first After reducing.（4）The two-step ion exchange process is used to chemically temper the glass-ceramic samples,and the optimal chemical tempering process parameters are determined as follows:the first step of chemical strengthening is 430℃/4h,the second step of chemical strengthening is 410℃/2h;At this time,the surface compressive stress of the glass-ceramic is 593.4MPa,the depth of the stress layer is 114.1μm,the flexural strength is 389MPa;the increase rate of the flexural strength is 82.6%.（5）Extending the time and temperature of the first chemical strengthening and the second chemical strengthening can increase the compressive stress depth of glass ceramics;but if the chemical strengthening time is too long,the chemical strengthening temperature will be too high due to the stress relaxation effect caused by glass relaxation,Resulting in a reduction in surface stress.In addition,combined with XRD and SEM analysis,during the chemical strengthening process,the surface of the glass-ceramics undergoes a transformation from the crystalline phase to the amorphous phase,which increases the residual glass phase on the surface of the glass-ceramics.