Si₃N₄/Inconel600 Partial Liquid Phase Diffusion Bonding

To obtain Si₃N₄ /Inconel600 joint with high temperature stability under lower bonding temperature, the Partial Liquid Phase Diffusion Bonding (PLPDB) new technology was developed based on asymmetry interlayer Nb/Cu/Ni for this joint. The mechanical behavior, microstructure and interface reaction of Si₃N₄ /Inconel600 was also investigated detailedly in this paper.The asymmetry interlayer Nb/Cu/Ni is designed by experiments to the bonding of Si₃N₄ /Tnconel600 system. The joint with high temperature resistance was prepared by using vacuum diffusion bonding equipment, and the structure of the joint consists of Nb-Ni metallic compounds as strengthening phases distributing on the matrix Cu-Ni alloy. An optimum parameters had been obtained as bonding temperature 1403K, bonding time 50min, bonding pressure 7.5MPa and cooling velocity 5K/min.The main processing factors had been highlighted for the bonding of Si₃N₄/Nb/Cu/Ni/Inconel600 system, such as the layer thickness of each Nb, Cu, Ni metal sheet, bonding temperature, bonding pressure, bonding time and cooling velocity. The layer thickness of each Nb, Cu and Ni sheet affected microstructure, properties and stress distribution in joint greatly, and the optimized thickness of Nb, Cu and Ni was 0.02mm, 0.05⁰.2mm and 0.045-0.12mm, respectively. The bonding temperature controlled interfacial reaction, diffusing rate of alloying element, microstructure and mechanical properties of joint. The bonding pressure was related to the contact area between solid phases, spreading of liquid metal on ceramic surface, thickness of reaction layer and concentration of low melt point metal in joint. The bonding time took a main role in the volume fraction of molten Cu layer, metallurgical reaction processing and the thickness of resulted reaction layer. The relationship in a parabola exists between bonding temperature, pressure, time and shear strength, respectively. Cooling velocity influenced directly the stress of interface and strength of the joint. With the increasing of cooling velocity, shear strength of the joint decreased linearly. In the present research, the highest shear strength of the joint reached up to 101.4MPa, taking on 84 percent of Si₃N₄ strength under the optimized bonding process and the thickness of Nb, Cu and Ni metal layer.The formation, microstructure characterization and distribution of phases in Si₃N₄/Nb/Cu/Ni/Inconel600 joint had been studied, and mechanism of interface reaction was discussed on emphases. Generally, there are two stages throughout the reaction of Si₃N₄ and interlayer. At the first stage, the liquid Cu enwraps Nb phase, and Nb diffuses into the Cu. The reaction layer of NbN and Nb₃Si was caused between Nb and Si₃N4. At the second stage, the Cu was melted completely. Element Ni diffuses into the liquid Cu-Nb alloy, and then a ternary Cu-Nb-Ni liquid alloy was formed. The Nb and Ni in the liquid alloy diffuse to the surface of ceramic, and reacting with Si₃N₄. The reaction products are NbN, Nb₃Si and Ni₃Si. Ni also combines with Nb to form a metallic compound NbNi₃ surrounding Nb.Thermodynamics and kinetics study had been carried out for the reaction between Si₃N₄ and interlayer. It is showed that Nb reacted with Si₃N₄ to form NbN...