Study On Process And Mechanism Of Diffusion Bonding Between SiC And Ti Under Alternating Electric Field And Pulsed Electric Field

SiC ceramic has a lot of superior properties such as high temperature, oxidation, corrosion resistance. Manufacturing ceramic/metal composite components can give full play to their excellent properties and have great significance to widen the application range of ceramic material. In this paper, in order to improve the efficiency and reduce connection conditions of diffusion bonding, an alternating electric field and pulse electric field were applied in the process of diffus ion bonding to optimize the Si C/Ti diffusion bonding process, reduce the diffusion bonding temperature and improve the quality of Si C/Ti diffusion bonding joints. At the same time, the influence law and mechanism of Si C/Ti diffusion bonding interfacial reaction was analyzed by using SEM, TEM and XRD, etc.Both AC voltage and bonding temperature affected the thickness of reaction layer, and the influence of reaction layer thickness to the shear performance ha d an optimum value. Eventually, the best AC voltage was 400 V under process parameters of 950℃/7.5MPa/1.5h, the shear strength reached 72.5MPa which increased by 59% than the joints without voltage, it proved that applying alternating voltage can effectively improve the quality of joints. The direction of voltage had a great effect on the interface, negative voltage inhibited element diffusion, the thickness of reaction layer was reduced which resulted in the decrease of bonding strength. Positive voltage boosted element diffusion, the joint quality was better.An orthogonal test was used to obtain the influence of pulse voltage parameters on joint performance, the results showed the order of various factors was pulse amplitude, duty ratio, frequency; the parameters were not independent but existed interactions. By the results, 400V/50%/5000 Hz was selected as the best pulse process parameter and its shear strength reached 77.93 MPa.Interfacial microstructure of SiC/Ti showed that the interface reaction generated new phase Ti C and Ti5Si3, and phase composition of interface structure from Si C to Ti was Si C/Fine grain zone/(Ti C+Ti5Si3)/Ti C/Ti. The fractures of Si C/Ti diffusion bonding joints were brittle cleavage fractures, the whole crack growth path was: the cracks growed at the weakest part of connection interface, and extended along the brittle compounds layer and Si C ceramic until the joints were destroyed.The important stage for getting reliable connection of Si C and Ti was solid diffusion reaction. Compared with no applying electric field, the reaction layer thickness had thickened after applying an electric field, which showed that the electric field could improve the reaction rate constant. The calculation of thermodynamic showed that the Gibbs free energy of chemical reaction was less than zero, which showed that the reaction could happen sponta neously; as could be seen from the reaction equilibrium constant Kθ value, the concentration of products was greater than the concentration of reactants when reaction reac hed equilibrium.