Fabrication and evaluation of Nb/Nb5Si3 microlaminate foils

Alloys of Nb and Nb5Si3, and in particular Nb/Nb5Si3 microlaminates, have potential as high-temperature materials. In this study, microlaminates of Nb and amorphous Nb-37.5 at. pct Si are magnetron sputter deposited from elemental Nb and polycrystalline Nb5Si3 targets. The microlaminates are heat treated at high temperatures to produce crystalline layers of Nb and Nb5Si3 that are flat, distinct, and stable for at least 3 hours at 1200 °C. The layers consist of textured Nb grains and equiaxed submicron Nb5Si3 grains. Initial room-temperature tensile tests indicate that the microlaminates have strengths similar to cast and extruded alloys of Nb and Nb5Si3. The fracture mode of the Nb layers is dependent on the Nb layer thickness, with thin layers failing in a ductile manner and thick layers failing by cleavage. The Nb layers bridge periodic cracks in the Nb5Si3 layers, and using a shear lag analysis, the tensile strength of Nb5Si3 is estimated. The results indicate that microstructurally stable and mechanically robust microlaminates of Nb and Nb5Si3 can be fabricated by sputter deposition with a high-temperature heat treatment. The processing, microstructure, and mechanical properties of these microlaminates are discussed.