1. Analysis of niobium material
Konrad Eiler
22/02/2016

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

3. Circular weld Nb
Specimen “R”
Specimen “180˚”
[1]
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4. 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

5. Circular weld Nb – metallography
180˚ Linear misalignment Level B: ℎ≤0.3 mm [2]
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6. Circular weld Nb – hardness profile
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7. Circular weld Nb – Conclusions
Imperfections comply with acceptance level B of ISO
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

8. 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
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9. 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
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10. Nb H8 Heraeus – Tensile testing
Ductility improved, but too low
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11. Nb H8 Heraeus – Hardness
Vickers hardness through the rod's cross-section
Very high deviation, inhomogeneous microstructure, highest hardness in the centre
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12. Nb H8 Heraeus – Results Microstructure still not fully recrystallisedRT
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

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