Transient liquid phase diffusion bonding of 6061-13 vol.% SiCp composite using Cu powder interlayer: mechanism and interface characterization

Transient liquid phase diffusion bonding of an extruded 6061-13 vol.% SiCp composite at 560 °C, 0.2 MPa, using a 50-μm thick copper powder interlayer with 20 min, 1 h, 2 h, 3 h, and 6 h hold times has been investigated. The isothermal solidification and homogenization of the bond region occurred with 3 and 6 h holding, respectively. During isothermal solidification, smaller SiC particles (size range: 11–13 μm) were pushed by the moving solid/liquid interface and segregated around the bond centerline, whereas bigger SiC particles (size range: 24–33 μm) were engulfed. During isothermal solidification, the bigger SiC particles locally hindered the solidification front movement causing grain refinement. The kinetics of isothermal solidification, representing the displacement of the solid/liquid interface (y, in μm) as a function of time (t, in s), followed a power-law relationship: y = 35 t 0.22. According to this kinetic equation, the effective diffusivity of copper in composite system was found to be about 105 times higher than the lattice diffusivity indicating the dominance of short circuit diffusion through the defect-rich particle/matrix interface. Ultrasonic investigation of the bond interface indicated that the signal attenuation was strongly correlated with the width of the segregated layer-a feature that decreased with the increasing bonding time. The completion of isothermal solidification was indicated by a sharp rise in the received signal amplitude with a negligible attenuation.