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Vacuum Brazing of K9 Glass and 2507 Stainless Steel

1 Introduction

K9 glass is a ceramic optical borosilicate glass with excellent optical properties, good chemical stability, low density, extremely high glass transition temperature (Tg≈719℃) and low cost. Therefore, it is a commonly used optical and microsystem material, which can fabricate micro- and nano-scale microstructures and microdevices on K9 glass, and can be used as optical substrates in high-power laser systems, window materials for optical devices, lasers and optical devices. Lenses and prisms for devices, and have been widely used in commercial optics and aerospace.

However, K9 glass is a brittle material and is a typical difficult-to-machine material. Therefore, in order to expand the application of K9 glass in many fields such as optoelectronic microwave technology and diffractive optical elements, it is necessary to connect it with itself or metal materials to prepare complex structural parts. K9 glass is often used for structural parts connected with stainless steel. Among them, the pitting corrosion index of 2507 duplex steel is higher than 40, which belongs to super duplex stainless steel and has excellent corrosion resistance and strength characteristics. Therefore, the connection of K9 glass with 2507 stainless steel is very important for the application of K9 glass in many fields. Compared with gluing and mechanical connection, brazing has the characteristics of firm connection and good air tightness. Compared with other welding methods, brazing has the advantages of low temperature, simple operation and can relieve the residual stress of welded joints. Among them, active brazing can use the reaction of active elements and glass to solve the problem of difficult wetting of glass and form reliable joints.

The vacuum brazing connection test of K9 glass and 2507 stainless steel was carried out using SnAgCu-Ti composite brazing filler metal containing different mass fractions of active element Ti, and the effect of Ti content on the interface structure and mechanical properties of the joint was analyzed.

The brazing process curve is shown in the figure. First, the temperature is raised to 500℃ at a heating rate of 20℃/min, and the temperature is maintained for 10 min. The soldering temperature was 675℃and kept for 10 min. Then, the temperature was lowered to 200℃ at a cooling rate of 5℃/min, and cooled to room temperature with the furnace. The vacuum degree of the whole brazing process is lower than 3×10-3 Pa, and a pressure of 1 MPa is applied on the surface of the C/C composite material to ensure the good contact between the base metal and the brazing filler metal.

2 Interface structure of brazed joints

The figure below shows the interface structure of the joint obtained by using SnAgCu-4%Ti composite solder at 675℃and holding for 10 min. It can be seen from the figure that the joint is well connected, the structure is uniform and dense, and there are no cracks and holes. The solder reacts with the base metal on both sides to form various compounds.

2.1 The interface microstructure of the brazed joint obtained by using SnAgCu-4%Ti composite brazing filler metal at 675℃ for 10 min is 2507 stainless steel/FeSn2/FeSn/Sn(s,s)/Ti-Sn/K9 glass.

2.2 The addition of Ti element has an important influence on the interface structure of the joint. With the increase of Ti content, Fe-Sn compounds in the brazing joints increased and gradually became dispersed, and Ti-Sn compounds dispersed in Sn(s,s) increased, which promoted the connection of brazed joints.

2.3 Shear strength and fracture analysis of brazed joints

In order to analyze the effect of Ti content in SnAgCu-x%Ti solder on the mechanical properties of 2507 stainless steel-K9 glass brazing joints, at room temperature, an Instron5967 universal material testing machine was used to test different Ti contents at 675℃ for 10 min. The obtained brazed joints were tested for shear strength, and the results are shown in Fig. It can be seen from the figure that with the increase of Ti content in the composite brazing filler metal, the shear strength increases gradually. When the content of Ti in the SnAgCu-Ti composite brazing filler metal is 4%, the brazing temperature is 675℃, and the holding time is 10 min, a large amount of Fe-Sn compounds and Ti-Sn compounds are dispersed in the brazing joint. The reaction layer formed by K9 glass is thicker, so the maximum shear strength obtained by the brazed joint is 7.3 MPa.

In order to study the relationship between the joint properties and the interface structure, the fractures of joints with different titanium contents were analyzed. The frontal photos of the stainless steel side of the brazed joint obtained with the Ti content of 0%, 2%, and 4% respectively. It can be seen that along the direction of the applied shear force, the brazed joints break at the K9 glass and extend into the brazing filler metal. Offset in glass.

3 Conclusions

(1) The vacuum brazing of K9 glass and 2507 stainless steel was achieved by using SnAgCu-x%Ti composite brazing filler metals with different Ti contents at 675℃/10 min. The typical interface structure of the joint was 2507 stainless steel/FeSn2/FeSn/ Sn(s,s)/Ti-Sn/K9 glass.

(2) With the increase of Ti content in the composite solder, the Fe-Sn compounds in the interface structure increase and gradually become dispersed, and the Ti-Sn compounds dispersed in Sn(s, s) increase, and the degree of uniformity of the joint structure is improved. , the shear strength is increased.

(3) When the Ti content in the solder is 4%, the maximum shear strength of the joint is 7.3 MPa under the condition of 675℃/10 min. The brazed joint broke through the K9 glass and extended into the brazing filler metal.

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