Microstructure And Properties Of Vacuum Brazed Joint For Mo-Cu Alloy And Cr18-Ni8Stainless Steel

In this work, the vacuum brazing of Mo-Cu alloy and Crl8-Ni8stainless steel was carried out with Ag-Cu-Ti, Cu-Mn-Co and Ni-based filler metal(Ni-Cr-P, Ni-Cr-Si-B) and the microstructure and properties of Mo-Cu/Cr18-Ni8brazed joint was analyzed. The study would provied theory and experiment basis, as well as has great application value and theoretical significance for the engineering application of Mo-Cu alloy and Crl8-Ni8stainless steel.The microstructure, diffusion and distribution of element, microhardness, shear strength and fracture characteristics were tested by means of optical microscope(OM), scanning electron microscope(SEM), energy dispersive system(EDS), microhardness tester and microcomputer control electron universal testing machines.The results showed that Ag-Cu-Ti, Cu-Mn-Co and Ni-based filler metal(Ni-Cr-P, Ni-Cr-Si-B) had a good wetting with Mo-Cu alloy and Cr18-Ni8stainless steel and the vacuum brazed joint has no crack or micro-hole with good metallurgical bonded interface.The Ag-Cu-Ti filler metal brazed seam was mainly comprised of eutectic and Cu-rich phase and the microhardness of brazed joint was lower than that of Mo-Cu alloy and Cr18-Ni8stainless steel. The shearing strength of Mo-Cu/Cr18-Ni8joint was about75MPa and the shear fracture exhibited plastic feature with shear dimple. The flake crack initiated in the interface between braze seam and Cr18-Ni8stainless steel and propagated along the interface and even eutectic.The Cu-Mn-Co filler metal brazed seam was mainly composed of single Cu-Mn solid solution phase with good plasticity and the microhardness of brazed joint was lower than that of based metal. The shearing strength was192MPa and shear fracture exhibited mixed ductile-brittle fracture feature. The fracture originated from the brazing seam forming plastic fracture and crack propagated to the Cr18-Ni8 stainless steel shaping river pattern brittle fracture.The Ni-Cr-P filler metal brazed seam was mainly consist of Ni-Cr-P solid solution, Ni-P eutectic, Ni-Cr(Fe, Mo) solid solution, N15P2and Cr3P precipitated phase. The microhardness of brazed joint was higher than that of based metal and the Ni-P eutectic was the highest, reached560Hv. The shearing strength was155MPa and shear fracture exhibited mixed ductile-brittle fracture feature with transgranular fracture, ductile dimples and tearing edges. Fracture originated from interface between brazing seam and Mo-Cu alloy and crack propagated to the barzing seam.The Ni-Cr-Si-B filler metal brazed seam was mainly made up of y-Ni(Cu, Fe) solid solution, Ni-B eutectic, while Ni-B eutectic disappeared and formed single y-Ni solid solution phase in amorphous filler metal brazed seam; the microhardness of brazed joint was higher than that of based metal, which the Ni-B eutectic was the highest. When the brazing temperature was1040℃, the shearing strength was207MPa and shear fracture showed mixed tear fracture, cleavage fracture and transgranular fracture, which the fracture originated from interface beside Mo-Cu alloy. When the brazing temperature was1120℃, the shearing strength reached343MPa and shear fracture showed obvious brittle fracture. The fracture located at y-Ni(Cu, Fe) solid solution in center of brazed seam formed brittle fracture with micro-cleavage step.