Thermomechanical behavior at the interface of additive manufactured superalloy/titanium alloy multi-material structures with a copper interlayer

Interfacial defects (such as cracking and delamination) caused by thermal stress mismatches due to distinct thermophysical properties (such as melting point, thermal expansivity) of dissimilar materials are critical issues in multi-material structures fabricated by laser powder bed fusion (LPBF). A comprehensive understanding of the complex interfacial thermal behavior caused by distinct thermophysical properties of dissimilar materials is important for reducing stress concentrations, inhibiting interfacial defects and improving the interfacial bond strength. In this work, the thermal–mechanical behaviors at the interface of IN718-Ti6Al4V multi-material structures were investigated using a thermally coupled finite element model. The effects of laser power, scanning speed, and the addition of a CuCrZr interlayer between IN718 and Ti6Al4V on the interfacial temperature distribution, thermal cycling behavior and temperature gradient were investigated. The thermal and residual stress distribution at the interface of the IN718/Ti6Al4V and IN718/CuCrZr/Ti6Al4V multi-material structures during LPBF were further revealed. The results showed that the addition of the CuCrZr interlayer increased the temperature gradient at the interface, and the maximum temperature gradient value appeared at the CuCrZr/Ti6Al4V interface. Residual stress concentrations occurred at the interface during LPBF, and the maximum residual stress exceeded 400 MPa at the interface of the IN718/Ti6Al4V multi-material structure, while that was about 250 MPa at the interface of the IN718/CuCrZr/Ti6Al4V multi-material structure, indicating that the addition of the CuCrZr interlayer was conducive to reducing the concentration of residual stress at the interface. The interface morphology analysis showed that adding the CuCrZr interlayer can avoid cracking at the interface, promoting metallurgical bonding between IN718 and Ti6Al4V. This work may enhance the basic understanding of improving the bonding strength of multi-material interfaces fabricated by LPBF, and provide a solution for manufacturing difficult-to-bond materials by LPBF.