Interfacial Microstructure Control Of Si₃N₄Ceramics Brazed With Amorphous Filler Metal And Cu Middle Layer

In this research, Ti40Zr25CuB0.2amorphous filler metal was made by single-rollrapidly-cooled equipment. Ti40Zr25CuB0.2amorphous filler metal directly and Cu foiladded as middle layer were used to connect Si3N4ceramics. The interfacial microstructureof Si3N4/TiZrCuB/Si3N4joint and Si3N4/TiZrCuB/Cu/TiZrCuB/Si3N4joint were studiedseparately. The effect of brazing parameters and Cu thickness on interfacial microstructureof Si3N4/TiZrCuB/Cu/TiZrCuB/Si3N4joints were analyzed in detail. Thermodynamicanalysis and growth kinetics of interfacial reaction of Si3N4/Si3N4joint were discussed. Onthis basis, the brazing parameters selection model was established. Furthermore, theformation mechanism of the joint was analyzed.During the heating process, amorphous filler alloy melted and Ti at the interfacereacted with Si3N4and formed the TiN interfacial reaction layer which was the importantcondition for realizing reliable connection. The typical interfacial microstructure ofSi3N4/TiZrCuB/Si3N4joint and Si3N4/TiZrCuB/Cu/TiZrCuB/Si3N4joint were Si3N4/TiN/Ti-Si+Zr-Si/Cu-Ti、Cu-Zr、Ti-Si+Zr-Si and Si3N4/TiN(Ti-Si)/Cu-Ti/Cu-Zr、Cu-Ti、α-Cu、Ti-Si+Zr-Si respectively.The results show that adjusting the brazing parameters can control the interfacialmicrostructure of Si3N4/TiZrCuB/Cu/TiZrCuB/Si3N4joints. With increasing brazingtemperature and holding time, the average thickness of TiN reaction layer increases, andthe interfacial reaction layer morphology changes from jagged to flat and becomescontinuous and compact gradually. At the same time, the growing Cu-Ti compoundsmigrate from the interface to the brazing seam center, while Zr-Si and Ti-Si compounds aregrowing from granular into block. Under brazing parameter of1253K×30min, with thethickness of Cu foil increasing, the average thickness of TiN reaction layer decreases, whileTi-Si compounds gradually divorces from TiN reaction layer to brazing seam center and themorphology changes from flake to granular. Furthermore, the other structures in brazingseam center gradually grew up whose morphology also changes. The brazing seam widthalso broadens after narrowing.Study on growth kinetics of interfacial reaction layer of Si3N4/TiZrCuB/Cu/TiZrCuB/Si3N4joint shows that the growth of interfacial reaction layer obeyed the parabola lawgoverned by the diffusion of participating elements. The growth coefficient at brazing temperature of1253K was determined to be2.3×10-8m/s1/2, the corresponding activationenergy of growth was424.01kJ/mol between the temperature1253K and1323K.The mathematical model of Si3N4/TiZrCuB/Cu/TiZrCuB/Si3N4brazing process wasestablished to choose brazing parameters. At the selected brazing temperature, the optimalthickness of reaction layerZ Caccording to the test results and the literature data. On thisbasis, the corresponding thicknessW1of the amorphous filler metal cuold be determined.Then the best heating time and the thickness of copper foil could be determined accordingtoW1.