Transient Liquid Phase Diffusion Bonding of Stainless Steel 304 Using Copper and Alominum Filler Alloys

Abstract

   Transient liquid phase diffusion bonding of stainless steel 304 has been performed using copper and aluminum interlayers in vacuum atmosphere at different temperatures. Interfacial microstructures were examined by scanning electron microscope, electron probe microanalysis, and X-ray diffraction. Microhardness and tensile tests were used to evaluate the mechanical properties. Results showed that the mechanical properties of the bond made by copper interlayer in vacuum were higher than that of made with aluminium interlayer. The poor mechanical properties of the bonds were associated with the formation of intermetallics within the bond region. In the optimum condition, a maximum tensile strength of 225.45 MPa, along with 16.08% ductility, were obtained for the diffusion bonded joint processed at 650°C. By holding the parent alloy at the bonding temperature for longer period, complete isothermal solidification was likely to occur. The diffusion of the main elements from the interlayers into the base metal at the bonding temperatures was the main controlling factor pertaining to the microstractural evolution of the joint interface. Selecting the appropriate bonding temperature to achieve a maximum concentration of the melting point depressants was dependent on the time of isothermal solidification.