Mechanical properties, microstructure, and texture of electron beam butt welds in high purity niobium

The effects of Electron Beam Welding on solidification microstructure, texture, microhardness and mechanical properties were investigated in high purity niobium weld specimens. The welds have an equiaxed microstructure with a 1 mm grain size in the fusion zone, 100 μm in the heat affected zone (HAZ) and 50 μm in the parent metal. The fusion zone had slightly higher microhardness values despite having a large grain size, while the unaffected material had the lowest microhardness. The texture in the weld consisted of a strong {111} fiber texture in the center and a mix of {111} - {100} components on the surface. Tensile tests of specimens gave σ_y = 60 MPa, but the UTS and elongation for weld specimens were lower than the parent material (137 vs. 165 MPa, 32% vs. 58%). The properties and microstructure of the weld are discussed in terms of optimizing the SRF cavity.