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