Temperature-gradient transient liquid phase bonding under low pressure

Temperature gradient transient liquid phase bonding (TG-TLP bonding) of 45MnMoB steel was carried out under low pressure using an iron base interlayer. The maximum deformation caused by the pressure was 1%. The bond microstructure was analyzed using EPMA, SEM and EDS, and the effects of pressure and temperature gradient on the bond interface morphologies and strength were also studied. The results show that applying low pressure during TG-TLP bonding can result in an “ideal joint” in 3 minutes, which is free of bond interface and identical in composition to that of base metal. Some insoluble oxide particles are observed in the bond made with a 5 °C/cm temperature gradient, and tensile strength of the bond is 75% of that of the base metal. Few oxide particles and impurities are found in the bond made with a 50 °C/cm temperature gradient, and the bond fails in the base metal. Compared with planar interface made by conventional TLP bonding and non-planar interface made by TG-TLP bonding, TG-TLP bonding under low pressure can produce a homogeneous joint free of interface, and the bond strength is equivalent to that of the base metal.