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Development of a Nonchromate
Structural Adhesive Bond
Primer
Mark Jaworowski
UTRC
2014 AsetsDefense meeting
2
Overview: Chromated Structural Adhesive Bond Primers
• Nominally 5 microns thick
• Prevent corrosion of base metal
• Applied to porous anodized surface
• Overcoated with non-inhibited epoxy adhesive
• High adhesive bond strength required for life of product
• Used in load bearing applications in flight-critical
hardware
• Anodized surface / primer interface stability is critical
• Typically 5% or less SrCrO4 by weight as sprayed
Fan Case Internal Bonding
Helicopter main rotor,
blade pockets, swashplate
Adhesive bond primer / anodize interface
All-composite propellers
Engine nacelles
Aerostructures
3
Previous testing of chromate free adhesive bond primers
Chromate inhibited Non chromate inhibited
168 hours ASTM B117 •Three companies (3M,
Cytec, Henkel) produce
aerospace structural
adhesive bond primers
•Long-running surveillance
of chromate-free alternatives
by UTC companies shows
weak corrosion inhibition
• (A) strontium
chromate- inhibited
bond primer, 2024 Al,
336 hours
• (B) Cytec BR6700-1,
2024 Al, 168 hours
• Inhibition technology
appears “low tech”: alkali
silicate, zinc phosphate
SEM: Cytec BR6700-1 (As-rec’d)
EDX: Cytec BR6700-1 (As-rec’d)
C
O
Al
Zn Al
CaSi
ClP
Element At% Atomic
ratio
Possbile
component
AlK 3.92 43.56
SiK 1.09 12.11
PK 0.09 1.00
ClK 0.17 1.89
CaK 0.79 8.78
ZnK 0.19 2.11
Cytec BR 6700-1 (As-rec'd)
Ca2SiO4,
CaAlSiO3,
ZnO
SEM: Cytec BR6700-1 (As-rec’d)SEM: Cytec BR6700-1 (As-rec’d)
EDX: Cytec BR6700-1 (As-rec’d)
C
O
Al
Zn Al
CaSi
ClP
EDX: Cytec BR6700-1 (As-rec’d)EDX: Cytec BR6700-1 (As-rec’d)
C
O
Al
Zn Al
CaSi
ClP
Element At% Atomic
ratio
Possbile
component
AlK 3.92 43.56
SiK 1.09 12.11
PK 0.09 1.00
ClK 0.17 1.89
CaK 0.79 8.78
ZnK 0.19 2.11
Cytec BR 6700-1 (As-rec'd)
Ca2SiO4,
CaAlSiO3,
ZnO
SEM: Cytec BR 6700-1 (post-test
scribe region) EDX: Cytec BR 6700-1
(post-test scribe region)Al
ZnZn CaPSi
Element At% Atomic ratio Comment
AlK 33.14 552.33
SiK 0.2 3.33
PK 0.17 2.83
CaK 0.09 1.50
MnK 0.06 1.00
CuK 0.24 4.00
ZnK 0.21 3.50
Zn, P,
Ca, and
Si
migrated
Cytec BR 6700-1 (post-test
scribe region)
SEM: Cytec BR 6700-1 (post-test
scribe region)
SEM: Cytec BR 6700-1 (post-test
scribe region) EDX: Cytec BR 6700-1
(post-test scribe region)Al
ZnZn CaPSi
EDX: Cytec BR 6700-1
(post-test scribe region)Al
ZnZn CaPSi
Element At% Atomic ratio Comment
AlK 33.14 552.33
SiK 0.2 3.33
PK 0.17 2.83
CaK 0.09 1.50
MnK 0.06 1.00
CuK 0.24 4.00
ZnK 0.21 3.50
Zn, P,
Ca, and
Si
migrated
Cytec BR 6700-1 (post-test
scribe region)
Development timeline for UTC Chromate-Free Adhesive Bond Primer
4
1999 -2000: UTRC / P&W Development of Concept
2001-2002 – UTRC / P&W
Joint Program Solubility
Regulation
2006 UTRC Capability
Project 7000-series Al
Performance Improvement
2009-2014 UTRC /
P&W/ 3M Product
Development and
Qualification
14121086420
2.0
1.5
1.0
0.5
0.0
-0.5
-1.0
-1.5
-2.0
Mo - Cl - H2O - System at 25.00 C
pH
Eh (Volts)
Mo
MoCl2OMoO2
MoO4(-2a)
14121086420
2.0
1.5
1.0
0.5
0.0
-0.5
-1.0
-1.5
-2.0
Ce - Cl - H2O - System at 25.00 C
pH
Eh (Volts)
CeClO
CeH2
CeO1.81
CeO2
Ce(+3a)
14121086420
2.0
1.5
1.0
0.5
0.0
-0.5
-1.0
-1.5
-2.0
Mn - Cl - H2O - System at 25.00 C
pH
Eh (Volts)
Mn
MnO2
Mn2O3Mn3O4
Mn(OH)2Mn(+2a)
MnO4(-a)
14121086420
2.0
1.5
1.0
0.5
0.0
-0.5
-1.0
-1.5
-2.0
Cr - Cl - H2O - System at 25.00 C
pH
Eh (Volts)
Cr
CrO2
Cr2O3
Cr(+2a)
CrCl2(+a)
CrO4(-2a)
Cr2O7(-2a)
Cr(OH)4(-a)
Nothing as good as Cr 6+…
14121086420
2.0
1.5
1.0
0.5
0.0
-0.5
-1.0
-1.5
-2.0
Ce - Mo - W - H2O - System at 25.00 C
C:\HSC5\EpH\CeMoW25.iep pH
Eh (Volts)
CeH2
Ce2(WO4)3
CeO2
Ce(+3a)
CeO(+a)
ELEMENTS Molality Pressure
Ce 1.000E+00 1.000E+00
Mo 1.000E+00 1.000E+00
W 1.000E+00 1.000E+00
Except multiple inhibitors?
Cerous citrate complex
regulates solubility of
multiple inhibitors
7705 Al / EcoTuff™
After corrosion test
Bright deposits:
50 wt% W + Zn
mixed oxide
3M Commercial
EW5000AS(P)3M Lab Batch
EW5000AS(L)
UTC EcoTuff®
Inhibitor
EW5000ET 3M Alt 1 3M Alt 2
EC3917
chromated
control
AS
TM
B117 e
xposu
re tim
e, hours
2000
1
500 1000 5
00
Optimized for multiple alloys Extensive corrosion and
mechanical property testing
Specification for engine use (EW-5000ET), testing of
developmental sol gel compatible primer (EW-5005)
5
Corrosion Science Model used to Develop Non Chromate Inhibitor
Thermochemical Strategy for Multimode Inhibitor
6
109876543
1.0
0.8
0.6
0.4
0.2
0.0
Initial pH
Co
nce
ntr
ati
on
, m
mo
l/lit
er
Zn 0.0 0
Zn 0.0 1
Zn 0.2 0
Zn 0.2 1
Species PO2 mol/liter
[NaCl],
Zn 2+
109876543
0.5
0.4
0.3
0.2
0.1
0.0
Initial pH
Co
nce
ntr
ati
on
, m
mo
l/lit
er
Mo 0.0 0
Mo 0.0 1
Mo 0.2 0
Mo 0.2 1
Species PO2 mol/liter
[NaCl],
MoO4 2-
109876543
0.30
0.25
0.20
0.15
0.10
0.05
0.00
Initial pH
Co
nce
ntr
ati
on
, m
mo
l/lit
er
Ce 0.0 0
Ce 0.0 1
Ce 0.2 0
Ce 0.2 1
Species PO2 mol/liter
[NaCl],
Ce 3+
Solubility test set-up
Syringe for in-
situ sampling
manifold
Test
flaskWater bath for
temperature
control
Thermocouple
Thermochemical identification
of inhibition systemCerous citrate chelation
complex regulates solubility
14121086420
1.8
1.3
0.8
0.3
-0.2
-0.7
-1.2
-1.7
-2.2
Ce - Al - Mo - W - H2O - System at 25.00 C
C:\HSC4\AlCeMoW2.iep pH
E(Ag/AgCl) (Volts)
CeH2
Ce2(WO4)3
CeO2
Ce(+3a)
CeO(+a)
ELEMENTS Molality Pressure
Al 1.000E+00 1.000E+00
Ce 1.000E-02 1.000E+00
Mo 1.000E-02 1.000E+00
W 1.000E-02 1.000E+00
Ce2(MoO4)3
Target solubilities of separate corrosion inhibiter achieved
Electrokinetic Confirmation of Active Inhibition in Coatings
7
Schematic of defect production and samples for salt spray (a) and EIS test (b).
Al2023-T3
Conversion coating
Primer
Top view
(b)
WC tip0.1-0.2 mm
Top view
(a)
WC tip0.1-0.2 mm
Dynamic damage testing of trial primers Static DC Testing on Bare Al
10 -9
10 -8
10 -7
10 -6
10 -5
10 -4
10 -3
10 -2
-1.00
-0.75
-0.50
-0.25
I (Amps/cm 2 )
E (
Volts)
EcoTuff® Ce 3+ /MoO 4
2 - /WO 4 2 - (I)
CrO 4 2 -
NaCl
Pitting potential improved
0.1m M
10 m M
- 0.35
AA2024 - T3 exposed to Ar - deaerated solutions
10-9 10-8 10-7 10-6 10-5 10-4 10-3 10-2-1.8
-1.6
-1.4
-1.2
-1.0
-0.8
-0.6
I (Amps/cm2)
E (
Volts)
EcoTuff®
CrO42-
Ce3+
Ce3+/MoO42-/WO4
2-(I)
Al2024-T3 exposed O2 saturated solutions
Cathodic inhibition comparable to Cr 6+
3M / P&W / UTRC Corrosion Test Results PAA treated 2024-T3 Al
8
3M Commercial
EW5000AS(P) 3M Lab Batch
EW5000AS(L)
UTC EcoTuff®
Inhibitor
EW-5000ET 3M Alt 1 3M Alt 2
EC3917
chromated
control
AS
TM
B11
7 e
xp
osu
re tim
e, h
ou
rs
20
00
1
50
0 1
00
0 5
00
2014 R&D 100 Award to UTRC / P&W / 3M Team
9
Back row (L to R):
Mark Jaworowski, UTRC, Michael Kryzman, UTRC
Front row (L to R):
Xiaomei Yu, Sikorsky Aircraft Corporation, Weilong Zhang, UTRC
Promila Bhatia,, Pratt & Whitney
Other UTRC Team members:
Sara Arsenault
Tom Garosshen
Steve Gore
Foster Lamm
Vince Nardone
Xia Tang
Other P&W team Members:
Thomas Hanlon
Camelia Galos
Alex Korzh
Nathalie Laurent
Ray Martina
John Putnam
Charlie Watson
3M Team Members:
Lance Chen
Eric Forbes
Michael S. Newman (Primary Contact)
Dmitriy Salinkov
Pete Steinhagen