Adverse effects of post-heat treatment on the interfacial bonding strength of direct laser deposition Inconel 625/1045 composites

Interfacial bonding strength is critical to the service life of components in the remanufacturing field. To identify the interfacial mechanical properties, a nickel-based Inconel 625 alloy powder was deposited on the AISI 1045 steel substrate by direct laser deposition. The effects of post-heat treatment on the phase transformation, composition segregation and residual stress releasing near the interface were investigated. A series of microstructural characterizations, such as SEM, FE-SEM, EDS and XRD, were used. By uniaxial tensile experiments, the interfacial bonding strength with/without post-heat treatment were compared, we found that the interfacial bonding strength of original specimen (556.8 MPa) was stronger than that of post-heat treatment (452.3 MPa). This was attributed to the fact that the thermal expansion coefficient of Inconel 625 powder (α(d) = 14.7) was less than that of the AISI 1045 substrate (α(s) = 15.6), resulting in the compressive residual stress at the edge of interface. After post-heat treatment, the release of beneficial compressive residual stress and the change of phase composition near the interface were the reasons for the decrease of interfacial bonding strength. These results indicated that post-heat treatment is not suitable for all heterogeneous bonding materials. This kind of material matching (α(d) < α(s)) is more advantageous to remanufacturing field.