Joining Dissimilar Ni and Nb Alloys via Transition Layer

A transition material layer is introduced between the Ni-based alloy and Nb-based alloy to serve as an intermediary that is compatible with both materials. This transition layer prevents direct contact between the thermodynamically incompatible Ni and Nb alloys, thereby avoiding spallation and cracks while enabling successful fabrication through additive manufacturing processes.

The composition of the transition material varies through its thickness, creating a compositional gradient that changes from being more Ni-compatible at the Ni-alloy interface to more Nb-compatible at the Nb-alloy interface. This local variation in material properties allows each region of the transition layer to be optimized for compatibility with its adjacent material, resolving the thermodynamic incompatibility issue.

The transition material acts as a mediator that enables direct joining of Ni-based and Nb-based alloys through additive manufacturing. By selecting a transition material with appropriate intermediate properties and compatibility with both alloys, the process achieves direct joining without the defects associated with conventional functionally graded transitions.

The composition parameters of the transition material are specifically selected and controlled to prevent the formation of non-equilibrium phases and localized cracks during additive manufacturing. The transition material's composition is designed to remain within stable phase regions during the thermal cycling of the fabrication process, thereby achieving defect-free fabrication.