Effect of brazing temperature on the interfacial microstructure and mechanical properties of GH3039 joint brazed with electroless Ni–P filler metal

Vacuum brazing of GH3039 nickel-based alloy with Ni–P filler metal was conducted at different brazing temperature. The Ni–P filler metal with a thickness of 10.4 μm was prepared by electroless plating technique, and the lap joints of GH3039 alloy were obtained. The microstructures and phase compositions of GH3039/Ni–P/GH3039 joints under different brazing temperature were characterized by optical microscopy (OM), scanning electron microscopy (SEM), and X-ray diffraction (XRD). The shear strengths of brazed joints were evaluated by tensile testing machine. According to the different microstructural features, GH3039/Ni–P/GH3039 joint was separated into two regions: solid solution region (region I: Ni_ss) adjacent to base metal (BM) and brittle microstructure (region II: Ni₃P + Ni_ss/Ni₃P eutectic) in the middle zone. With the increase of brazing temperature, the width of region I (solid solution zone) increased but the thickness of region II (brittle microstructure zone) decreased gradually. The formation of a thinner brittle eutectic zone improved the mechanical properties of GH3039/Ni–P/GH3039 joint. As a result, the maximum shear strength of GH3039/Ni–P/GH3039 joint brazed at 1150 °C could reach 174 MPa. Correspondingly, the fracture mode of GH3039/Ni–P/GH3039 joint changed from cleavage fracture to quasi-cleavage fracture with the increased brazing temperature.