ISOSTATIC DIFFUSION BONDING OF MICRODUPLEX STAINLESS-STEEL

Studies of isostatic diffusion bonding of microduplex stainless steel have been made for two surface finishes at temperatures in the range 1200-1320 K for times of up to 10 h and pressures of up to 2-8 MPa. Bond quality has been assessed using metallography, compressive lap shear testing, and scanning electron microscopy of the fracture faces of lap shear test pieces. Sound bonds were observed with recrystallisation across the bondline for a range of conditions, although it was always possible to detect the interface because of the presence of small oxide particles. Bonding at temperatures < 1273 K led to hardening and embrittlement of the steel owing to a phase formation. Comparison of experimental bonding times for a pressure of 2.1 MPa with times predicted by an isostatic diffusion bonding model showed substantial discrepancies. Although the discrepancies could partly be a result of uncertainties in the material parameters used in the model, it is probable that the interfacial oxide has acted as a diffusion barrier reducing the rate of mass transfer, thereby increasing experimental bonding times.