Brazing Of Silicon Nitride Ceramic High-temperature Activity Of Amorphous Brazing Study

The vacuum brazing of Si3N4 ceramic was carried out with Ti40Zr25Cu20Ni15 amorphous filler metal. The interface microstructure was investigated by means of SEM and EDS. The results showed, the element Ti is more active than Zr, and first reacted with the Si3N4 ceramic in Ti-Zr-Ni-Cu active brazing alloy. The interface reaction layer is made up of TiN abut on the ceramic and the Ti-Si,Zr-Si compounds. The influence of brazing temperature, brazing time and pressure, on joint room temperature strength was also studied, and it was exhibited by the thickness and consistency of the reaction layer. The joint exhibited the highest room temperature strength of 160 MPa which was brazed at 1323K for 120min with a pressure of 400Pa. Under the same experiment conditions, the room temperature strength of the joint brazed with amorphous filler metal increased a lot compared with the crystalline. When the test temperature is 573K, the joint exhibited a highest high temperature strength of 126 MPa, then the joint strength descended with the higher test temperature, and reduced rapidly when the test temperature come to 673K.In order to improve the joint strength, a series of brazing alloy was designed on the basis of Ti40Zr25Cu20Ni15. Their results of wetting test on Si3N4 ceramic showed, the brazing alloy can't wetting the Si3N4 ceramic if the the quantity of Ti less than 30% in weight. Its wetting ability improved by adding a little quantity of B,Si, and adding 2%B in weight exhibit a best effect. A larger number of Ni was added in order to improve the high temperature strength, and Zr was also added to enhance the glass forming ability. So TiZr20Ni20Cu20B0.2,TiZr20Ni25Cu15B0.2 were selected as the optimized results, and they were prepared into amorphous foils successfully. EDS,DTA results of amorphous allloy showed their element distribution is very uniform and the solidus and liquidus temperature were a little lower than the crystal brazing alloy, and the wetting ability of amorphous alloy is superior to the crystal alloy in 5×10-3Pa fine vacuum experiment condition. Compared with the joint strength brazed with Ti40Zr25Cu20Ni15 amorphous alloy, the room temperature strength of TiZr20Ni20Cu20B0.2,TiZr20Ni25Cu15B0.2 amorphous alloy brazing joint is almost the same, but the high temperature strength was improved. Their high temperature strengths were 93MPa and 88MPa respectively at test temperature of 773K, while the Ti40Zr25Ni15Cu20 brazing joint collapse at 773K.