Study On Technology And Mechanism Of Brazing2Si-B-3C-N Ceramic To Niobimm

In this paper, AgCuTi solder was used to realize2Si-B-3C-N ceramic itselfconnection and to get a reliable connection of ceramic and Nb. This paper studied theinterface reaction mechanism of AgCuTi solder and2Si-B-3C-N ceramic.The lowexpansion coefficient intermediate layers and the composite solder were used to easethe residual stress in the brazed joints of2Si-B-3C-N ceramic and Nb. This paperanalysised the mechanism of the residual stress, as well as how the two methodsalleviate the residual stress of the joints. Then a more excellent intermediate layersystem was designed to achieve a more reliable connection of2Si-B-3C-N ceramicand Nb.When using AgCuTi solder to braze2Si-B-3C-N ceramic, Ti content should beselected5wt.%of the AgCuTi solder, the best process parameters: temperature of thebrazing:900oC, holding time:10min. The main products of the interface reactionwere TiC+TiSi+TiSi2. The tissue of joint was SiC+BN (C)/TiC/TiSi+TiSi2/Ag(s)+Cu (s)/TiSi+TiSi2/TiC/SiC+BN (C).In the connection of directly braze2Si-B-3C-N ceramics to metals Nb, the jointhas a too large residual stress to make a cracking in the ceramic. This method can notachieve a reliable connection of2Si-B-3C-N ceramic and metal Nb. The intermediatelayer with low coefficient of expansion can reduce the residual stress in the joint,when the thickness of added Mo foil greater than100μm, the ceramic did not crackafter welding. Joint strength increased with a bigger thickness of the Mo foil.Thismethod by adding a low expansion coefficient layer to the joint, so that the maximumresidual stress in the joint was transferred from the ceramic to the Mo foil layer. Thismethod reduced the stress in the joint, the,most vulnerable part of the joint, andplayed a relieve residual stress effects; The composite solder by adding h-BN powderto AgCuTi solder to produce TiN and TiB in situ,so that reduced the residual stress inthe joint. The joint strength altered with the changeing of the h-BN content inAgCuTi solder. Mechanical propertie of the joint of2Si-B-3C-N ceramic and metalNb was getted with adding3wt.%h-BN to AgCuTi solder, the greatest shear strengthof the joint is69MPa. The joint fracture was in the ceramic, the composite solderdirectly reduced thermal expansion coefficient of the solder layer, thereby alleviatingthe difference between the2Si-B-3C-N ceramic and AgCuTi solder, which wasbenefit to get a joint with a smaller residual stress.A method with a combination of composite solder and intermediate layer withlow coefficient of expansion was studied in this paper. When used AgCuTi solder (h-BN3wt.%) and150μm thickness Mo Nb foil as intermediate connection layer tobarze Si-B-3C-N ceramics and Nb, this paper getted a joints with the mechanicalproperties preferably the maximum shear strength up to89MPa, and under theseconditions, fracture location of brazed joints was not in a single layer, the fracturepath was also not in the same level, this tortuous fracture needed a bigger work offracture. So this fracture required a greater energy applied load, and these brazedjoints had more excellent mechanical properties.