Research On Element Diffusion And Interface Reaction Of BNi-2 Vacuum Brazing 15-5PH

The paper is a study on the BNi-2 brazed 15-5PH precipitation hardening stainless steel.After welding, by using the means: scanning electron microscopy, energy spectrum analysis,electron microprobe, X-ray diffraction analysis, analyzed the impact of brazing temperature,holding time, brazing joint clearance and cooling way on microstructure and properties of brazing joint, and the diffusion of interface elements.The results showed that: Amorphous filler BNi-2 would be completely liquefied when the brazing temperature rose to 982℃. In the cooling process, binary eutectic reaction occurred firstly(L→γ+Ni3B). Ternary eutectic reaction occurred when cooled to 993℃(L→γ+Ni3B+CrB). The brazed joint of BNi-2 brazed 15-5PH could be divided into four zones: Diffusion-affected zone(DAZ), Interface reaction zone(IRZ), Isothermal solidification zone(ISZ) and Athermally solidified zone(AZS).Along with the brazing temperature increasing, the number of black compound in the center of brazing joint was gradually decreasing. The form of black compound phase gradually changed from continuous network to intermittent strips and then transformed into thin strips in more decentralized. The black phases generated in the center of joint mainly are boride and small amounts of silicide. Furthermore, as the brazing temperature rising, the number of precipitation phase increased and the matrix crystal grains grew significantly.The diffusion trend of interface elements under different welding temperature was consistent. But along with the increasing the brazing temperature, the element diffusion tendencywere flattened, fluctuations reduced, element diffusion distance increased and the width of each region of brazing joints were significantly increased.Holding time determined the degree of elements diffusion of filler, at low temperature increased holding time, brazing gap significantly increased. However, at high temperature,increased holding time, the number of compounds and brazing gap varied little.when the element diffused equilibrium after holding a while, diffusion of elements no longer occurred even though increasing holding time. The process adopted single piece of brazing filler metal containing nickel-based solid solution, when the process adopted three pieces of brazing filler metal, black compounds phase exited in central zone again.With the holding time increasing, the number of black compound in joint of Oil quenching and furnace cooling were decreased, the change of the brazing clearance wasfirstly decreased and then increased, but under the condition of oil quenching the number of black phase in joint significantly more than the number of furnace cooling, the joint tensile strength of furnace cooling better than oil quenching.