Brazing Process And Mechanism Of ZrB₂-SiC Composite Ceramic Using Pd-Co-based Filler

The Pd-Co based alloy solders added certain content of Ni, Ti or V were usedto braze ZrB₂-SiC ceramic. Effects of the content of the third component, holdingtime and brazing temperature on microstructure and properties were investgated.The brazing process and reaction mechanism were revealed.The joints brazed using Pd-Co solder consisted of three parts:（I） A diffusionzone in ZrB₂-SiC matrix, where ceramic matrix was decomposed into ZrB₂due tothe reaction between Pd and Co elements with SiC reinforcement.（II） brazingseam in which Co-Si, and Pd-Si phases distributed.（III） ZrB₂-SiC matrix. Thebreakdown of SiC reinforcement attributing to the reaction with the solder materialcaused the drop of properties of the matrix. The maximum bonding strength of77MPa could be achieved for the ioints brazed with Pd30%-Co70%at1270C for30min.Pd-Co-V and Pd-Co-Ti filler alloy were used to join ZrB₂-SiC ceramics,considering that V or Ti could react with SiC to form V-C or Ti-B containingreaction layer to prohibit the exceed reaction between Co and SiC. It could befound that the thickness of the diffusion zone decreased significantly with Ti or Vcontent increasing. When using Pd-Co-V solder, a large stripe-shaped black V-Cphase occur in the seam, which greatly deteriorated the bonding strength. Whenusing Pd-Co-Ti, Ti reacted with element B in the base material to generated Ti-Bphase at the interface of the base material, which inhibited the reaction betweenthe solider and SiC at certain extent. Correspondingly, a relatively better jointcould be obtained whose four-point bending strength was85MPa.Pd-Co-Ni solder was also selected to braze ZrB₂-SiC ceramics. The additionof Ni element did not changed the width of reaction layer significantly. With theincrease in Ni content, the joint strength firstly increased and then decreased.Varying the holding time and brazing temperature, it could be found that theoptimized parameters could be determined, i.e.1270C brazing and5min holding.Under this brazing process, a four-point bending strength of120MPa could bereached for the joint using （Pd30-Co70）74Ni26solder.