Diffusion bonding of titanium alloy to micro-duplex stainless steel using a nickel alloy interlayer: Interface microstructure and strength properties

In the present study, diffusion bonding of titanium alloy and micro-duplex stainless steel with a nickel alloy interlayer was carried out in the temperature range of 800–950 °C for 45 min under the compressive stress of 4 MPa in a vacuum. The bond interfaces were characterised by scanning electron microscopy, electron probe microanalyzer and X-ray diffraction analysis. The layer wise Ni3Ti, NiTi and NiTi2 intermetallics were observed at the nickel alloy/titanium alloy interface and irregular shaped particles of Fe22Mo20Ni45Ti13 was observed in the Ni3Ti intermetallic layer. At 950 °C processing temperature, black island of β-Ti phase has been observed in the NiTi2 intermetallics. However, the stainless steel/nickel alloy interface indicates the free of intermetallics phase. Fracture surface observed that, failure takes place through the NiTi2 phase at the NiA–TiA interface when bonding was processed up to 900 °C, however, failure takes place through NiTi2 and β-Ti phase mixture for the diffusion joints processed at 950 °C. Joint strength was evaluated and maximum tensile strength of ∼560 MPa and shear strength of ∼415 MPa along with ∼8.3% ductility were obtained for the diffusion couple processed at 900 °C for 45 min.