Proposal on a novel NbTi/Cu multilayer sheet composite concept for superconducting applications

An Nb-layer-free NbTi/Cu multilayer composite is proposed for superconducting shielding applications. Cold-rolled Nb–53 wt% Ti and oxygen-free high-thermal-conductivity (OFHC) Cu sheets were assembled in a copper cassette and processed into a structurally homogeneous composite with a final thickness of 0.5 mm by hot rolling at 700 °C, followed by cold rolling at room temperature. Microstructural analyses reveal excellent chemical and morphological stability of the NbTi/Cu interfaces. No Cu–Ti intermetallic compound formation is detected after intermediate ageing at 375 °C for 12 h at 1 mm thickness, nor after prolonged heat treatment in the final state. This stability is preserved despite the intentional omission of a Nb diffusion barrier layer. Extended ageing for 672 h induces the formation of non-equilibrium Widmanstätten α-Ti precipitates within the NbTi matrix, accompanied by a high dislocation density in both the precipitates and the parent β-NbTi phase. These features provide effective flux-pinning sites without compromising interfacial integrity. The Nb-free multilayer design simplifies processing, reduces material cost, and enhances the stabilising role of copper, offering a robust microstructural platform for superconducting shield applications.