Application and challenge of glass and titanium alloy welding technology

In the extreme environment of aerospace optical window, a 0.1mm gap between a piece of K9 glass with a diameter of 30cm and the titanium alloy frame is enough to cause the failure of the whole satellite in orbit. This seemingly small interface is a problem that has not been solved in the field of materials science for decades – how to make the hard and fragile glass and the strong but high melting point titanium alloy achieve atomic level reliable bonding.

1、 Application scenarios and technical bottlenecks

In such cutting-edge fields as satellite optical systems, implantable medical devices, high-precision sensors, the quality of the connection between glass and titanium alloys directly affects the life and reliability of equipment. The traditional adhesive will release volatile organic compounds in the vacuum environment, resulting in optical system pollution; It will gradually age and become invalid in the temperature environment; In the building curtain wall, it faces the problem of hardening and embrittlement caused by ultraviolet radiation. What is more difficult is that the difference between the thermal expansion coefficient of the two materials is as high as 4-8 times (Glass approx 8.5×10⁻⁶/K , titanium alloy approx 9.5×10⁻⁶/K ）The shear stress caused by temperature fluctuation is enough to cause interface collapse.

2、 Breakthrough in laser welding technology

1. Surface modification and precise energy control

Qingdao University of Technology team deposited on titanium alloy surface by magnetron sputtering TiO ₂ film The surface can be raised from 45mJ/m ² to 72mJ/m ², significantly enhancing the compatibility with quartz glass. Under the action of millisecond laser (30kHz repetition frequency), the interface forms a unique Ti Si mixed zone , through mechanical interlocking and chemical bonding, the shear strength is increased to 30.63MPa ——It is equivalent to 3 times of the traditional brazing strength. Jiangsu University found that the welding strength of TC4 titanium alloy with high borosilicate glass was improved after laser surface pretreatment to generate oxide layer 4x The fracture analysis showed that the titanium alloy debris remained on the glass side, which confirmed that the metallurgical bonding level was reached.

2. Fine balance of oxide film thickness

Suzhou University research revealed the double-edged sword effect of anodic oxidation: when the thickness of the oxide film on the surface of titanium alloy is 3-5 μ m, the composite structure of rutile type TiO ₂ and anatase type TiO ₂ can absorb laser energy and promote the formation of molten pool, and the welding strength is increased by 19%; However, when the film thickness increases to 20 μ m, the internal porosity increases, leading to the bonding strength Down 37% 。 At this time, energy diffusion occurs at the interface (Fig. 10), and the laser beam scatters in the loose layer, weakening the effective welding energy.

3、 Diffusion welding technology: pressure and temperature dance

For the low temperature application requirements of K9 glass and titanium alloy, diffusion welding technology achieves molecular level combination through three steps:

Electron beam texturing : At the frequency of 400-550Hz, the spiral wave electron beam is used to bombard the titanium surface to form micron anchor points
Vacuum high temperature oxidation : Hold at 700 ℃ for 20 minutes to form a dense oxide layer
Gradient pressure bonding : Keep the temperature at 600 ℃ and 35Pa for 2h to shorten the diffusion distance of interface atoms to 5Å（0.5nm） Metal bond bonding is realized within

This method was applied in an aerospace component enterprise in Shandong Province, and reduced the vacuum failure rate of optical windows from 0.8% to less than 0.02% per thousand hours.

4、 Low temperature connection technology innovation

With the help of 500V DC electric field, the low-temperature composite solder system developed by Harbin Institute of Technology (Bi ₂ O ∨ – B ₂ O ∨ – ZnO CaO Ti) has successfully applied Connection at 500 ℃ (Far lower than the melting point of titanium alloy 1668 ℃). Reactive Ti element reacts with SiO ₂ in glass to form Ti₅Si₃ , its coefficient of thermal expansion（ 7.2×10⁻⁶/K ）It is between glass and titanium alloy, forming a natural stress buffer layer. The strength retention rate of the joint reached 98.7% through the low temperature cycling test at – 50 ℃.

5、 Technical challenges and future directions

Difficulties in thermal stress control : When the building curtain wall glass (3m × 4m) is welded to the titanium frame, the thermal stress generated by the temperature difference between day and night of 60 ℃ exceeds 200MPa. Proposed by the team of Birmingham University Functionally gradient material interlayer Design, thermal expansion coefficient of gradient transition through Fe Ni alloy layer
Extreme environmental reliability : Adopted by Heriot Watt University Picosecond laser (Pulse width 1 picosecond=10 ⁻ ¹² s) Successfully welded quartz glass and titanium alloy at minus 90 ℃. The diameter of the melting zone formed by micro plasma is only 20 μ m, and the heat affected zone is 90% smaller than the traditional process
Intelligent process window : The online monitoring system for laser welding developed by Institute of Metals, Chinese Academy of Sciences Plasma spectral intensity And Bath oscillation frequency , real-time feedback regulating power (± 2W accuracy), so that the yield is increased to 95%

6、 Cross border application expansion

Neural interface device : 100 μ m thick borosilicate glass was welded with titanium microelectrode array, and the stable period of signal acquisition was extended from 3 months to 2 years after implantation into rat brain
Intelligent building curtain wall : Shanghai Central Building applies glass titanium alloy composite frame, reducing weight by 30% and improving wind pressure resistance by 25%
Deep space detector : The optical window of Chang’e-6 lunar lander adopts laser welded titanium alloy frame, which can withstand the test of 300 ℃ temperature difference between day and night on the lunar surface

The welding of glass and titanium alloy has evolved from simple material splicing to a precise control of intermolecular forces. When millisecond laser splashes nanoscale TiO ₂ grains on the surface of titanium alloy, when composite solder generates thermal expansion transition layer driven by electric field, and when picosecond laser creates microplasma bonding at minus 90 ℃ – the essence of these technological breakthroughs is to build an atomic bridge across the material gap between silicon dioxide network and titanium lattice. In the future, with the deep integration of intelligent control technology and gradient material design, glass titanium alloy welding will unlock more application scenarios in extreme environments, allowing brittle glass and tough titanium to bloom new life in aerospace, medical implant and other fields.