P1259062220TgQsF

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An investigation about different permanent
deformation of Nb3Sn and NbTi stacks
E. Valladolid Gallego, CERN TS/MME
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• 2 stacks of Rutherford type cables insulated
  with a 15-mm-wide, 60-mm-thick quartz fiber
  tape.
• Tape first treated in air at 350 C-15 h, then
  wrapped around cables
• Wrapping of two layers without overlay.
• Stacks of 10 insulated cables alternated to
  compensate keystone
• Nb3Sn heat treated 660 C-120 h in pure Ar
• Both finally vacuum impregnated with epoxy resin
  and cured (95 C-12 h 110 C 48 h)
• Cables made of - NbTi used in LHC quadrupole
  magnets
• - Nb3Sn for quadrupole model at CEA

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Goal - Try to understand the different
permanent deformation of NbTi and Nb3Sn stacks
measured at Saclay

• Stress-strain curves measured in compression
  along azimuthal direction
• Pre-load 2.5 kN
• Very first loading not understood (irregular
  strand positioning, more refined observations
  necessary)

M. Reytier et al., Characterization of the
Thermo-Mechanical Behavior of Insulated Cable
Stacks Representative of Accelerator Magnet
Coils, IEEE Trans Appl. Superconductivity 11
(2001) 3066
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Procedure Observation of the individual wires,
depth (and width) of the grooves present on the
cables (after chemical dissolution the epoxy
resin). Tools used 1. Metrology measurements
(Mitutoyo SV-C3100 profilometer) 2.
Microhardness test (Leitz Wetzler device) 3.
MEB observation (SEM LEO 430 microscope
EDX ISIS software)
1.
2.
3.
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Metrology measurements
We quantify the grooves present on the wires
measuring their depth and width (groove shape
determined to a significant extent by compressive
stress applied during the test?)
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SEM picture of the wire where the permanent
deformation experienced by the individual wires
in the stack is observed
Measurements of the distances between peaks
and valleys (profilemeter)
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Measurements of the distances between peaks and
valleys (depth), and width of the valleys
Depth Nb3Sn 0.058 0.009 NbTi 0.051
0.009
Width Nb3Sn 1.040 0.115 NbTi 0.907
0.060
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Microhardness test on Cu at 5 g (on wires from
cables of the tested stacks)
Average Nb3Sn 65 ?HV Average NbTi 96 ?HV
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-3 reference cables provided by CEA - NbTi
(same batch?) - Nb3Sn without thermal
treatment - Nb3Sn with thermal treatment
Nb3Sn
NbTi
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Reference samples from CEA
Width Nb3Sn_NT 1.04 0.07 Nb3Sn_T
1.03 0.05 NbTi 1.06 0.10
Depth Nb3Sn_NT 0.056 0.005 Nb3Sn_T
0.060 0.005 NbTi 0.056 0.009
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MEB observations
Nb3Sn from stacks, , absence of major indents
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Grooves in the surface of Nb3Sn from stacks
? Cable manufacturing?
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NbTi from stacks, absence of major indents
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Nb3Sn_NT (reference)
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Nb3Sn_T (reference)
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NbTi (reference)
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Conclusions - as expected, Cu matrix in Nb3Sn
wires has lower hardness than in NbTi - deeper
grooves are measured in compressed Nb3Sn than in
compressed NbTi - nevertheless, no measurable
evolution of the groove shape can be measured in
compressed Nb3Sn compared to the reference
sample. Groove depth is mainly explained as
associated to the cable manufacturing process
- difference in groove shape of
compressed and reference NbTi is probably due to
the different origin of the samples otherwise
the evolution would go in the wrong direction -
major local indents not observed - despite the
different hardness of the Cu, differences in
behaviour are in absolute terms small (0.7
permanent deformation ? 12 ?m on individual
wires!) can be hardly measured by the resolution
of available technique, even on a basis of an
average of several indents
Thanks to D. Pugnat, D. Glaude, D. Gagniere, A.
Gerardin, G. Arnau, S. Sgobba
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Conclusions_2 - presence of a 316L core in
Nb3Sn does it play a major role? - behaviour
of the resin sample?