Analysis of niobium material Konrad Eiler 22/02/2016

Contents Nb/Nb 3 mm circular weld by Niowave Metallography Hardness Nb H8 from Heraeus Tensile tests Konrad Eiler

Circular weld Nb Specimen “R” Specimen “180˚” [1] Konrad Eiler

Circular weld Nb – metallography Overlap region (recouvrement) Excessive weld metal Level B: ℎ≤0.65 mm [2] Thickness too low on one side – not related to welding Konrad Eiler

Circular weld Nb – metallography 180˚ Linear misalignment Level B: ℎ≤0.3 mm [2] Konrad Eiler

Circular weld Nb – hardness profile Konrad Eiler

Circular weld Nb – Conclusions Imperfections comply with acceptance level B of ISO 13919-2 Low local thickness of 2.5 mm not related to welding No increased hardness in weld pool Higher hardness in one sheet (ca. 80 HV10) Konrad Eiler

Nb H8 Heraeus – History [3] Context: Nb rod from Heraeus, Ø133 mm x 635 mm For forming of beam port by Niowave Very low ductility and high yield strength Material was cold-worked and insufficiently annealed Rod has been sent back for re-annealing Konrad Eiler

Nb H8 Heraeus – Metallography Recrystallisation into the former grains (before re- annealing) Higher degree of recrystallisation after re-anneal Still grains in the cm range in the centre Deformation bands visible Centre Outer radius Konrad Eiler

Nb H8 Heraeus – Tensile testing Ductility improved, but too low Konrad Eiler

Nb H8 Heraeus – Hardness Vickers hardness through the rod's cross-section Very high deviation, inhomogeneous microstructure, highest hardness in the centre Konrad Eiler

Nb H8 Heraeus – Results Microstructure still not fully recrystallised RT HV10 Rp0.2 [MPa] Rm [MPa] Ag [%] A [%] Samples 58 130 167 7.3 19.8 Spec [4] <60 50-100 >140 - >30 Microstructure still not fully recrystallised Tensile specimen taken from the same location broke at the same position Properties after re-annealing still not fulfilling the specification Ductility too low Konrad Eiler

References [1] ISO 15614-11, Specification and qualification of welding procedures for metallic materials – Welding procedure test – Part 11: Electron and laser beam welding. ISO, 2002. [2] ISO 13919-2, Welding – Electron and laser beam welded joints – Guidance on quality levels for imperfections – Part 2: Aluminium and its weldable alloys. ISO, 2001. [3] K. Eiler: Analysis of large grain size, low ductility niobium material. EDMS 1556016, 2015. [4] Technical Specification 3301: Pure niobium bars for superconducting applications (RRR 300 grade). EDMS 1476934, 2015. Konrad Eiler