Research On The Technology And Mechanism Of Glass Filler Joining Transparent Magnesium Aluminum Spinel Ceramics

Transparent magnesium aluminum spinel ceramics（Mg Al₂O₄）have the advantages of high strength,high hardness,good chemical stability,and high transmittance in infrared visible light bands.It is an ideal material for manufacturing transparent armor,laser emitter windows and other components.However,due to the inherent brittleness of ceramic materials,it is difficult to prepare large-sized or complex shaped components.Joining technology is an important method to solve this problem.In view of the adjustable coefficient of thermal expansion（CTE）of glass filler and the good chemical compatibility between glass filler and ceramic materials,uses glass filler to join transparent Mg Al₂O₄ceramics in this paper.This article designs Zn O-Al₂O₃-Si O₂（ZAS）and Ca O-Al₂O₃-Si O₂（CAS）based glass fillers,and analyzes the physicochemical properties and crystallization behavior of the glass filler.On this basis,the influence of joining technology on the microstructure and mechanical properties of joints was studied,and the evolution mechanism of joint microstructure and fracture mechanism were revealed.The peak crystallization temperature（Tp）of ZAS glass is 786℃,corresponding to the crystallization phase of Zn Al₂O₄.The CTE of ZAS microcrystalline glass after 1000℃crystallization treatment is 6.9×10^-6/℃.In addition,ZAS glass has good wettability on the surface of Mg Al₂O₄.On this basis,the effect of cooling process on the microstructure and mechanical properties of the joint was studied.The results indicate that the bending strength of the joint increases with the increase of Zn Al₂O₄ crystal content in the weld seam.When crystallization treatment is introduced in the cooling process,a large number of fine Zn Al₂O₄crystals can be precipitated in the joint weld,which makes the coefficient of thermal expansion of the weld more matching with Mg Al₂O₄ ceramics.The optimal bending strength of the joint reaches 201MPa.There are two crystallization peaks in CAS glass at 810℃and 892℃,corresponding to Li Al Si₂O₆ and Ca Si O₃,respectively.The CTE of CAS glass filler and Mg Al₂O₄ ceramic at30-600℃is 7.9×10^-6/℃.And CAS glass has good wettability on the surface of Mg Al₂O₄ceramics.The results of the connection experiment indicate that when the joining temperature is low（1250℃）,the flowability of the glass filler is poor,and there are pore defects at the joint welds.When the joining temperature is 1400℃,the dissolution and diffusion of elements between the filler and the ceramic intensify,causing changes in the composition of the weld seam,leading to an increase in CTE differences between the weld seam and the ceramic,and the formation of cracks at the ceramic.The lower cooling rate（5-10℃/min）leads to the precipitation of Ca Al₂Si₂O₈ and Mg₂Al₄Si₅O₁₈ crystals with low expansion coefficients in the weld,which damages the mechanical properties of the joint.When the joining temperature is 1300-1350℃and the cooling rate is 15℃/min,the bending strength of the joint reaches 181-189 MPa,and the transmittance of the joint at a wavelength of 1000 nm reaches 82.1%.