Study On One-step Chemical Strengthened Of Large Thickness LAS Glass For Aviation Transparent Parts

Lithium aluminosilicate glass（LAS glass）has become an ideal main structural material for aviation transparent parts except sodium calcium silicate glass and sodium aluminosilicate glass due to its low density,high elastic modulus and excellent ion-exchange performance.At present,due to the blockade of foreign technology,the related research on the influence of the change of chemical strengthened process parameters of large thickness LAS glass on the ion-exchange law and mechanical properties of LAS glass for aviation transparent parts in Chinese domestic is blank,which can’t provide support for the engineering application of LAS glass in aviation transparent parts.In order to change this situation,two typical large thickness（3 mm,8 mm）LAS glasses were used in this paper.The effects of chemical strengthened process,Li⁺concentration enrichment in molten salt and high temperature treatment on the properties of chemical strengthened LAS glasses were studied.The effects of chemical strengthened process on the chemical strengthened properties of large thickness LAS glass were explored by adjusting the chemical strengthened time,temperature and molten salt ratio.When the chemical enhancement temperature is 400℃,the chemical enhancement time is 8-16 h,and the chemical enhancement molten salt is pure KNO₃molten salt,the chemical enhancement performance of 3 mm LAS glass is better.When the chemical enhancement temperature is 400℃,the chemical enhancement time is 24 h,and the chemical enhancement molten salt is pure KNO₃molten salt,the chemical enhancement performance of 8 mm LAS glass is the best.After chemical strengthened progress,the surface compressive stress,depth of layer and bending strength of LAS glass are better than those of NAS glass with the same thickness.The one-step chemical enhancement process can meet the actual airworthiness requirements of LAS glass for aviation transparent parts.By introducing different contents of Li⁺into the chemically enhanced molten salt to simulate the failure process of molten salt,the effect of Li⁺enrichment in molten salt on the chemical enhancement performance of LAS glass was explored.The increase of Li⁺concentration in the molten salt will have a significant effect on the chemical enhancement of LAS glass.When the Li⁺concentration in the molten salt reaches 4800 ppm,the surface compressive stress,flexural strength and hardness of the chemically enhanced LAS glass are significantly reduced.The change of Li⁺concentration in molten salt has no obvious effect on the stress layer depth and transmittance of chemically enhanced LAS glass.Na₃PO₄was selected as the impurity remover to explore the purification effect of Na₃PO₄on chemical strengthened molten salt,and the purification effect was evaluated by the change of chemical enhancement performance of LAS glass.Na₃PO₄can effectively remove Li⁺from the failed molten salt.When 1 wt%Na₃PO₄was added to the failed molten salt,the surface compressive stress of 3 mm chemically enhanced LAS glass was significantly restored.Na₃PO₄is insoluble in molten salt.The increase of Na₃PO₄content will cause the turbidity of molten salt,and the transmittance of chemically enhanced LAS glass will be affected to some extent.The effect of high temperature environment on the properties of chemically enhanced LAS glass was explored by simulating the high temperature environment of coating.High temperature heat treatment has a significant effect on the properties of chemically enhanced LAS glass.With the increase of the number of high temperature heat treatment,the surface compressive stress,flexural strength and hardness of chemically enhanced LAS glass decrease continuously.However,compared with the current mainstream sodium aluminum silicon glass for aviation transparent parts,after the same number of high temperature heat treatment,LAS glass has the advantages of higher surface compressive stress,greater stress layer depth and greater bending strength.After one or two heat treatments,the surface compressive stress of chemically enhanced LAS glass remains above 800 MPa,which meets the actual airworthiness requirements.