Research On Process And Mechanism Of TC4/K9 Glass Diffusion Bonding Based On Metal Surface Oxidation

Metal and glass connectors are widely used in aerospace,biomedical and other fields.TC4 titanium alloy and K9 glass have good comprehensive mechanical properties and optical properties.Their connectors are suitable for use as materials for plane mirrors of important optical components in various aerospace vehicles or astronomical telescopes.However,due to the large difference in the physical and chemical properties of TC4 and K9 glass,effective connections cannot be formed when direct diffusion bonding.The metallurgical joints can be formed by pretreatment of metals.Based on the surface oxidation mechanism of titanium and TC4,this paper conducts vacuum diffusion bonding on TC4 and K9 glass.Studies the diffusion process,and reveals the interface di ffusion mechanism.In this paper,Ti and TC4 were oxidized at 700?1000°C for 2h?6h respectively.Using scanning electron microscope(SEM),energy spectrometer(EDS),X-ray diffraction(XRD),transmission electron microscope(TEM)and other methods to analyze the metal surface oxide layer.The results show that the oxide layer on the Ti surface is not oxidized at 700°C.The degree of oxidation is insufficient at800°C,and Ti remains on the surface,forming a disc ontinuous Ti-O oxide layer.Ti₆O,Ti₃O and Ti O are formed at 900°C,and most of them are transformed into Ti O₂ at 1000°C.Compared with pure Ti,the Al element in TC4 will be enriched inside the Ti-O layer as the oxidation reaction proceeds,and react with Ti element to form a Ti-Al-O compound.V element volatilizes when oxidized to generate V₂O₅.As the oxidation temperature increases from 800°C to 1000°C and time extends from 2h to 6h,the surface oxidation products change from needle-like and granular distribution to worm-like and island-like distribution.The grain size and the thickness of the oxide layer gradually i ncreased,and the thickness of the oxide layer increased to 7.2?m and 14.7?m,respectively.Based on the surface oxidation process of tit anium and titanium alloys.When oxidized for 2h,the vacuum diffusion bonding process of Ti/K9 glass and TC4/K9glass were studied under pressure of 2500,4500 and 6500Pa at 680,700 and720°C,respectively.The microscopic morphology,interface element di stribution,interface structure,mechanical properties and fracture behavior of diffusion bonding joints are studied to reveal the mechanism of diffusion bonding.The results showed that as the diffusion bonding temperature increased from 680°C to720°C,the joint structure was densified first and then small holes appeared.The average shear strength was up to 27.9MPa.T he fracture at 680°C is mainly brittle fracture,and the main fracture mode at 700°C and 720°C is spalling,and the fracture has a cup-shaped vertebral structure.The interface connection mechanism of TC4/K9 glass is mainly two aspects:active element diff usion and chemical reaction.The Ti element on the metal side diffuses to the glass side,and the elements such as Si,O,Na and K on the g lass side diffuse to the metal side.Compounds such as Ti₅Si₃ and Ti Si₂ are formed at the interface.In addition,an amorphous transition layer is formed between the glass and the interface layer,with a thickness of about 100nm,forming a metallurgical bo nded joint.Finally,the ABAQUS finite element simulation software is used to study the stress change process of TC4 and K9 glass conne ctors of different sized and shapes from 700°C to room temperature.The results show that when the stress is concentrated on the base of the TC4 metal bracket.As the diameter of the reflector increases from 2.1m to 2.5m,the internal residual stress of th e weldment increases from 161.9MPa to 253.7MPa.When the mirror diameter is 2.1m and the crystal thickness increases from 0.1m to 0.3m,the residual stress decreases form161.9MPa to 117.8MPa.The hexagonal and circular hole structure is used to optimize the design of the metal substrate,the connecting parts have no obvious stress concentration,and the weight reduction rat e reaches 63.96%,which provides a theoretical basis for practical applications.