Development of Electrochemical Machining (ECM) for Tungsten
Transcript of Development of Electrochemical Machining (ECM) for Tungsten
INSTITUTE FOR APPLIED MATERIALS - MATERIALS PROCESSES IAM-WPT | CORROSION DEPARTMENT
www.kit.eduKIT – University of the State of Baden-Württemberg andNational Research Center of the Helmholtz Association
Development of Electrochemical Machining (ECM) for Tungsten
J. Konys, W. Krauss, N. Holstein
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Contents:
Motivation for electrochemical machining (ECM)
Electrochemistry of tungsten
ECM of tungsten
S-ECM
C-ECM
Conclusions and recommendations
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Motivation for Electrochemical Processing (ECM) of TungstenTypical defects and failures in W parts by conventional machining
Primary machining defects
HHF results define needs for W-processing
Smooth surfacesNo defects from machiningNo sharp edges
Conventional machining is expensiveInnovative soft machining methods required
Crack growth at machining defect
Post HHF analyses of
mock-up EFREMOV.
Machining defect
caused failure
Mock up # 4
Secondary failures, growing under HHF load
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Electrochemical Reactins of TungstenW dissolution: EC oxidation
Basic Investigation
Anodic reactionW-dissolution
Application Cathodic reactionDeposition
Surface treatmentElectro-polishing,cleaning
Scale depositionbrazing e.g. W byNi protic
MachiningECM
Depositionaprotice.g. W or Ta
0,0001
0,001
0,01
0,1
1
10
100
1000
-0,75 -0,5 -0,25 0 0,25 0,5 0,75 1 1,25 1,5 1,75 2 2,25 2,5 2,75 3 3,25
E / V (Hg/HgSO4)
i /
mA
cm
-2
pH = 12,4
pH = 12
pH = 11
pH = 10
pH = 9
pH = 9
pH = 8
pH = 7
pH = 7
pH = 6
pH = 5
pH = 3
pH = 1
i = f(pH)
System: W / TCEE / Pt
v = 1 mV/s, 1000 U/min, d = 16 mm
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ECM Requirements
Electrolyte development
M-ECM: anode mask
process
C-ECM: cathode tool
ECM Advantages
No cracks by ECM
process
Surface polishing
residue-free metal
removal M-ECM for Slot array : UV-mask Novolak
cathode =
ECM working tool,
negative imagevertically mobile
anode = workpieceelectrolyte
agitation by microstep-motor
frameworkcathode guiding
++
--
C-ECM scheme
Processed workpiece
= ECM
Anode = workpiece
-
+
-
+
-
+
Cathode = ECM working tool
Anode = workpiece
--
++
--
++
--
++
C-ECM
2 H+ + 2e- → H2
Me → Me2+ + 2e-
MAIN DIFFERING FEATURES
M-ECM, S-ECM C-ECM
Technique Conventional installation Complex facility
Parameters Current x time = charge Charge + distance + steprate + convection
Cathode passive counter electrode active shaping component (by step motor)
Tool design 2-dim. mask (positive) 3-dim. electrode (negative)
Transformation +2-dim →+3-dim resp. +0-dim -3-dim → +3-dim
ECM for 3-D structuring | M-ECM => S-ECM + C-ECM
M-ECM
Mask processing UV-lithography Electrochemical Etching Structured workpiece
hn365 nm
++
--
M-ECM without resist masks = S-ECM
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ECM of W towards W/refractory-alloys
Dissolution ability of W-alloys by ECM electrolyte
-50
0
50
100
150
200
250
300
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400
450
500
550
-1 -0,8 -0,6 -0,4 -0,2 0 0,2 0,4 0,6 0,8 1 1,2 1,4 1,6 1,8 2 2,2 2,4 2,6 2,8 3
E / V (Hg/HgSO4)
i /
mA
cm
-2
W, pH = 12
WL10, pH = 12
Mo, pH = 12 b
Ta, pH = 12
Al, pH = 12
i = f(pH)
System: Me / 1,25 M N+NH3 / Pt
Me = W, Wla10, Mo, Ta, Al
v = 1 mV/s, 1000 U/min
Mo improves machinability / dissolution rate
Stable oxide forming elements (Ta) are less favorable for the electrolyte N-NH3
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Electrochemistry of tungstenInvestigation and development of ECM electrolytes
W0 -> W6+
tungsten metal
H HO
H H
H He-
e-
H HOH H
tungsten metal
OO
O W
O
O W
WO3 WO3 WO3 WO3 WO3WW
H+ H+
H+ H+ H+
H+H+
SEM0,0001
0,001
0,01
0,1
1
10
100
1000
-0,5 -0,25 0 0,25 0,5 0,75 1 1,25 1,5 1,75 2 2,25 2,5
Potential E [V vs. NHE]
i [m
Ac
m-2
]
pH = 12
pH = 11
pH = 10
pH = 9
pH = 8
pH = 7
pH = 6
pH = 3
pH = 1
Linear Scanning Voltametry (LSV)
Sytem: W / TCEE / Pt
Scan rate: 1 mV/sec
W + 3 H2O → WO3 + 6 H+ + 6 e-
W → W3+ + 3 e-
Does not take place !!!
H HO
H H
tungsten metal
OO
O W
O
O W
WO3 WO3 WO3 WO3 WO3WW
H-H
-
H H
tungsten metal
W W
WO42-
H-
H-
WO42-
WO42-
WO42-
Electrochemical investigations: Potentiostatic Linear Scanning Voltammetry
W + 2 H2O + 2 OH-→ WO42- + 6 H+ + 6 e-
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Electrochemical Tungsten Processing S-ECMS-ECM of surfaces
…on EDM-cut rod pieces
W as machined
S-ECM 15 min, 400 mA/cm2
In SEM
In SEMVIS
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Electro-chemical tungsten processing S-ECMS-ECM of surfaces
Single crystal pieces
Mechanical mirror
polishing
S-ECM, rising current densities
elaboration on z-orientation
Effect on sc-orientation: parameters of S-ECM mirror polishing
on one orientation cannot be applied unchanged to other orientation
Wittmann‘sche Etching structures rough, without any reflection Plain, partial reflection Plain, black = total reflection
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-50
0
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100
150
200
250
300
350
400
450
500
1 10 100 1000 10000 100000
Frequency /Hzd
elt
a
%
delta upper gap width
delta ground width
delta flank width
HF-Pulses in ECM of tungsten
Dependencies of measures from frequence
Extrapolation to HF = 00
Extrapoliert
depth
upper gap width
Flank width
ground gap width
Development of techniques to
generate high HF currents
C-ECM of tungsten Impact of pulse current effects
νννν = 10 Hz
pH = 10
0,4 mm
νννν = 1 kHz
pH = 10
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C-ECM of tungstenFabrication of 3-dim demonstrators
Parallel grooved structure Angled structures
Tool Tool
Cathode tool
Cathodic potential: no corrosion + mechanically contactless - no pressure
Working tool (every material, every design, every current) without any chemical,
elctrochemical,thermal, mechanical abrasion
TOOLS
Demonstrators:
Generated W-structures
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Anodic dissolution by ECM
Hz: 10000 1000 500 100 10 0
C-ECM:
Edge steepness as
Function of
pulse frequency νDesired
flank
profile
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-1000
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-800
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-600
-500
-400
-300
-200
-100
0
100
200
300
-2500250500750100012501500175020002250250027503000Abstand AE-GE / µµµµm
E / m
V (
Hg/H
gS
O4)
200 mA/cm2
100 mA/cm2
150 mA/cm2
50 mA/cm2
E = d(AE-GE)
System: W / SL1 / Pt
i = 200 mA/cm2, 1500 U/min, d0 = 3 mm
0,0001
0,001
0,01
0,1
1
10
100
1000
-0,5 -0,25 0 0,25 0,5 0,75 1 1,25 1,5 1,75 2 2,25 2,5Potential E [V vs. NHE]
i [m
Acm
-2]
pH = 12
pH = 11
pH = 10
pH = 9
pH = 8
pH = 7
pH = 6
pH = 3
pH = 1
Linear Scanning Voltametry (LSV)
Sytem: W / TCEE / Pt
Scan rate: 1 mV/sec
Quality improvement
W ���� WL 10, WTaMoX
Higher frequency of pulsed DC powerMobility control / reduction
Conductivity of electrolyte
Parameter dependencies
Smaller distance
tool – work piece
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Development of C-ECM tool for shaping
of micro-structured workpieces:
e.g. Castellation:
6-fold star,
Projected depth 6 mm, width 0,1 mm;
aspect ratio = 60
Design of cathode tool and
facility for castellation-shaping
C-ECM Castellation tool
Castellation cathode tool:
first prototype (brass foils)
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C-ECM European Patent EP 467
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Conclusions
Electro-Chemical Machining (ECM) of tungsten:
W can be successfully machined by ECM without chemical passivation
Three ECM branches selected for special applications (S-ECM, C-ECM M-ECM)
ECM shows strong dependency on DC pulse frequency and gap distance
High frequency technology in DC pulses is required for good accuracy
S-ECM can polish and optimize fine structured surfaces
Demonstrators fabricated by S-ECM and C-EC
MGeneral statement :
ECM is a well investigated technology for tungsten
Achievements (work progress) in agreement with work plan
ECM has an established status for industrial W-shaping
Achieved technical status allows tt to industrial scale, AND /OR….
Achieved patent EP 467 allows commercial exploitation
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Open questions
Actual and future work:
Accuracy improvement by high frequency (> 10 kHz range)
Analyses of conductivity impact on long range dissolution suppression
Application of not symmetrically pulse pause ratios of DC profiles
Investigations of new non-aqueous electrolyte systems (e. g. EMIM, IL)
Analyses of ECM application to W-Ta by improved electrolytes
Response / needs from discussions with industry
Testing of newest electro-mechanical tools and forced flow
Electrolyte regeneration
Integration of industries into ECM of W under patent application