Vacuum Science and Technology Radiation Heating for Vacuum Diffusion Welding of YAG and Ninth Five-Year Porcelain Qi Kangcheng (Department of Optoelectronic Technology, University of Electronic Science and Technology of Chengdu 610054) Diffusion welding in vacuum to YAG and ceramics. Adopting radiant heating method, the sealing air-tightness is better than 1013Pa m3 / s under the condition that the temperature is 600G and the pressure is 25N / mm2. The sealing strength is better than 1013Pa m3 / s.
With the advancement of science and technology and the improvement of living standards, large-screen, high-brightness, high-resolution information displays have been widely valued. CRT projection displays have advantages such as excellent image quality, simple structure, mature CRT manufacturing technology and driving technology, etc. So that it has a huge market advantage in the future large-screen information display field. High brightness and high resolution CRT projection tube is one of the core components of CRT projection TV.
At present, there are a variety of CRT projection TVs on the market, and they use 5-9 inch CRT projection tubes.
YAG single crystal has excellent thermal conductivity (thermal conductivity 0.14WAcmli), high visible light transmittance, and has excellent mechanical strength and insulation strength, therefore, it can be used as a light-emitting screen substrate material for projection tubes . Practice has proved that the 2mm thick YAG single crystal substrate can well meet the performance requirements of manufacturing 3 inch YAG projection tubes. Is this. Assemble the YAG substrate, Al ring (purity higher than 999%, thickness 0.1 ~ 0.2mm) and ceramic tube head, and put it in a vacuum system for diffusion welding. The vacuum chamber is provided with a pressure applying device which provides a constant pressure and a radiant heating device which heats the sealing member. Obviously, in order to ensure airtightness, the temperature and pressure in the circumferential direction of the seal should be as uniform as possible. The uniformity of the pressure is mainly guaranteed by the processing accuracy of the spinning device and the grinding accuracy of the ceramic parts. The uniformity of the temperature is guaranteed by the heating device as shown, middle 1, 2 are the pressure rods; they are the components to be sealed ; 4 is graphite ring; ring electric furnace; 6 is heat reflection shield; 7 is adjustable base. Relying on the experimental results of 2 21 The effect of sealing temperature, pressure and holding time on the sealing quality When the pressure is constant, increasing the sealing temperature, the plasticity of the Al ring is large, which is conducive to the closeness of the surface of Al and YAG, Al and ceramic At the same time, the diffusion coefficient of Al to YAG and ceramic surface and inside is large. Therefore, increasing the temperature will increase the sealing strength and air tightness. However, if the temperature is too high, Al may be extruded in a large amount. The extruded Al forms a tip discharge when the projection tube is working, which affects the reliability of the projection tube. At the same time, due to the increase of the diffusion amount, Al will be partially depleted at the sealing site and voids will appear, resulting in a decrease in vacuum tightness, and may also cause direct contact between the YAG and the ceramic, and the Al layer loses its due buffering and stress relaxation effects. , Resulting in that the sealing stress cannot be effectively relaxed or the YAG substrate burst.
Under the premise of ensuring the uniformity of the pressure, the application of pressure is conducive to improving the sealing airtightness. Therefore, the greater the pressure, the better, as long as the YAG single crystal substrate is not damaged or Al is extruded from the sealing portion in large amounts. Therefore, the pressure selected in the test is 5 ~ 25N / mm2, basically there is no phenomenon of YAG substrate crushing. Due to equipment limitations, no pressure experiment above 30N / mm2 was conducted.
For different sealing temperature and pressure, the air tightness is better than the probability curve of 1013Pam3 / s (detector limit). The rotation of the graphite ring coaxially to be sealed ensures the toe of the workpiece in the circumferential direction. The best sealing temperature and pressure are 6 vacuum science and technology. The airtightness is better than the probability and pressure of 2X 10-13Pam3 / s. The temperature relationship is 25N / mm2, and the sealing yield at this time is more than 90%.
The holding time (ie diffusion time) during welding should have a certain effect on the sealing quality. Prolonging the diffusion time and increasing the diffusion amount of Al are beneficial to improve the welding strength. However, from the perspective of sealing airtightness, under the conditions of 600C and 25N / mm2, after 3 to 5 minutes of diffusion, a sealing part with good airtightness can be obtained; as the diffusion time is long, the yield rate continues to increase ; The diffusion time is more than 15min, and the sealing yield has not been significantly improved. For safety reasons, 20 2.2 sealing area was selected for electron microscopy analysis, and the sealing parts were not ground after being broken. As can be seen from this photo, the granular structure of the ceramic near the boundary between Al and ceramic becomes very insignificant, and the voids between the particles disappear, indicating that Al has diffused into the ceramic and filled the gaps between the particles. The boundary line between Al and YAG is obvious, the boundary line is straight, and there is no evidence of Al diffusion into YAG. However, it can be clearly seen from the figure that the broken section of the Al layer is broken and the shadow is caused on the photo, but there is still a layer of bright white Al firmly attached to the YAG surface, indicating that the Al and YAG surfaces are tightly combined by diffusion Together, the bonding strength has exceeded the strength of Al itself. Therefore, diffusion welding with an Al ring can achieve sealing with good airtightness and relatively high strength.
SEM photos of the sealing area (from left to right are ceramics, AlYAG) 3 Conclusion Al can diffuse to the YAG surface and the ceramic surface and inside, combining YAG and ceramic to form a good airtight and high strength seal Pieces.
Diffusion temperature, pressure, and time are three mutually restrictive parameters. Under the premise of ensuring the heating uniformity and pressure uniformity of the sealing part, it is recommended to use the process conditions of diffusion temperature 600C, pressure 25N / mm2, time 20 ~ 25min.
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