Microstructural Evaluation of 410 SS/Cu Diffusion-Bonded Joint

In the present study, a grade of stainless steel (SS, 410) and copper plates were joined through diffusion bonding by using a nickel interlayer at temperature range of 800-950 degrees C. These were performed through pressing the specimens under a pressure of 12 MPa for 60 min under 1.33x10(-2) Pa (10(-4) torr) vacuum. The microstructure and phase constitution near the diffusion bonding interface of Cu/Ni and Ni/SS were studied by optical microscopy (OM), scanning electron microscopy (SEM), X-ray diffraction (XRD) and an elemental analyses through energy dispersive spectrometry (EDS). The results indicated that an obvious diffusion zone was formed near both Cu/Ni and Ni/SS interfaces during the vacuum diffusion bonding. The thickness of reaction layer in both interfaces was increased with increasing process temperature. The diffusion transition region near the Cu/Ni and Ni/SS interfaces consist of complete solid solution zone and various phases based on (Fe, Ni), (Fe, Cr, Ni) and (Fe, Cr), respectively. From EDS results, three different mixtures of phases were distinguished in SS-Ni interface. The activation energy and rate constant were determined for the growth of these reaction layers and the values become maximum for the {gamma Fe, Ni+alpha Fe+Cr} phase mixture.