coating system specification approach to non-chromium coatings · pigmented epoxy primer class n:...
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Coating System Specification Approach
to Non-Chromium CoatingsD I A N E B U H R M A S T E R , S E N I O R M A T E R I A L S E N G I N E E R
M A T E R I A L S A N D M A N U F A C T U R I N G D I R E C T O R A T E
O C T O B E R 2 0 1 9
Distribution A: Approved for public release: Distribution Unlimited. 88ABW‐2019‐4680, 25 Sep 2019
Outline• BLUF: Hexavalent Chromium Issue• Hierarchy of Controls• Non-Cr Coatings Are…• Salt Spray Conundrum• Path Forward• Summary
Distribution A: Approved for public release: Distribution Unlimited. 88ABW‐2019‐4680, 25 Sep 2019
Bottom Line Up-Front: The Hexavalent Chromium IssueCoatings systems contain hexavalent chromium (Cr6+)
Cr6+ is highly carcinogenic
Standard Polyurethane TopcoatHexavalent Chromium Pigmented Epoxy Primer
Standard Cr‐Free Pretreatment
Aerospace Aluminum Substrate
Old Way of Looking At Coatings
Distribution A: Approved for public release: Distribution Unlimited. 88ABW‐2019‐4680, 25 Sep 2019
Most Effective
LessEffectiveStandard Method
Reduce HazMat
Improved Facilities
Shift Rotation
Technology Development
Distribution A: Approved for public release: Distribution Unlimited. 88ABW‐2019‐4680, 25 Sep 2019
Technology Development: Non-Chromium Coatings
Replacement
Standard Polyurethane TopcoatNon‐Chromium Pigmented Epoxy Primer
Standard or Altenrate Cr‐Free Pretreatment
Aerospace Aluminum SubstrateBaCrO4
SrCrO4
H2CrO4New Way of Looking At Coatings
Non-Cr = Elements that are not Cr BaSO4
Cr3+Al3+Li+Mg2+
Y+/‐
ZrOPr6O11
Distribution A: Approved for public release: Distribution Unlimited. 88ABW‐2019‐4680, 25 Sep 2019
Military Specifications - Aircraft Standard
Polyurethane Topcoat
Class C: Hexavalent Chromium Pigmented Epoxy Primer
Class N: Engineering Approval Only, Tested over Cr Pretreatments
Standard PretreatmentUsually Cr6+, Some Cr3+,
*One Rare Earth Non‐Cr (2018)
Mix & Match
MIL‐PRF‐85285
MIL‐PRF‐23377
MIL‐DTL‐81706
H2CrO4
Distribution A: Approved for public release: Distribution Unlimited. 88ABW‐2019‐4680, 25 Sep 2019
Key Materials Properties – Previous DoD ApproachStandard
Polyurethane TopcoatClass C: Hexavalent Chromium
Pigmented Epoxy Primer
Class N: Engineering Approval Only, Tested over Cr Pretreatments
Standard PretreatmentUsually Cr6+, Some Cr3+,
*One Rare Earth Non‐Cr (2018)
Mix & Match
H2CrO4
Ultraviolet Light
Solvents
Aircraft Fluids
Humidity
Flexibility SoilingAdhesion
Aircraft FluidsAdhesion Solvents
FlexibilityCorrosion Resistance
Adhesion
Corrosion Resistance
Distribution A: Approved for public release: Distribution Unlimited. 88ABW‐2019‐4680, 25 Sep 2019
Key Materials Properties – AFRL ApproachStandard
Polyurethane TopcoatHexavalent Chromium Free PrimerChromium‐Free Pretreatment
Paired
Ultraviolet Light
Solvents
Aircraft Fluids
Humidity
Flexibility SoilingAdhesion
Aircraft FluidsAdhesion Solvents
FlexibilityCorrosion Resistance
Adhesion
Corrosion Resistance
Cr3+Al3+ Li+Mg2+
Y+/‐ZrOPr6O11
BaSO4Y+/‐Pr6O11
Glycidyl 3‐(trimethoxysilyl)propyl ether
Zirconium N‐propoxide
3M AC‐131
Henkel Bonderite 5200
AkzoNobelAluminum Rich Primer
HentzenPPG (Deft)
Effective as a SystemNot Mix & Match
Distribution A: Approved for public release: Distribution Unlimited. 88ABW‐2019‐4680, 25 Sep 2019
The “Salt Spray” ConundrumClass C: Hexavalent Chromium
Pigmented Epoxy Primer
Class N: Engineering Approval Only, Tested over Cr Pretreatments
Standard PretreatmentUsually Cr6+, Some Cr3+,
*One Rare Earth Non‐Cr (2018)
H2CrO4
Corrosion ResistanceCorrosion Resistance
MIL‐PRF‐23377MIL‐DTL‐81706
336 hours 2000 hours
Pretreatment only With and Without Topcoat
Exposure Cabinet
Distribution A: Approved for public release: Distribution Unlimited. 88ABW‐2019‐4680, 25 Sep 2019
The “Salt Spray” Conundrum
Zero Cr
Corrosion ResistanceCorrosion Resistance
MIL‐PRF‐23377MIL‐DTL‐81706
336 hours 2000 hours
Pretreatment only With and Without Topcoat
Chromium Free PrimerChromium‐Free Pretreatment
Exposure Cabinet“Passed” Outdoor
Exposure Testing “Failed”
Outdoor Exposure Testing
Distribution A: Approved for public release: Distribution Unlimited. 88ABW‐2019‐4680, 25 Sep 2019
The “Salt Spray” Conundrum
Corrosion Mechanism in Salt Spray Cabinet Testing Corrosion Mechanism in Outdoor Exposure Testing
Distribution A: Approved for public release: Distribution Unlimited. 88ABW‐2019‐4680, 25 Sep 2019
The “Salt Spray” Conundrum
Accelerated aging should not change the target aging mechanism!
Accelerated aging @ 100°F
21 days
Long‐term aging of an egg @ 80°F
1 year
Slide courtesy Dr. Greg SchoeppnerAFLCMC/EZFS.
Accelerated aging @ 212°F
8 min
Distribution A: Approved for public release: Distribution Unlimited. 88ABW‐2019‐4680, 25 Sep 2019
Path Forward to Non-Chromium Coatings
Replacement
Standard Polyurethane TopcoatNon‐Chromium Pigmented Epoxy Primer
Standard or Altenrate Cr‐Free Pretreatment
Aerospace Aluminum Substrate
BaCrO4
SrCrO4
H2CrO4
New Way of Looking At Coatings
Non-Cr = Elements that are not Cr
BaSO4
Cr3+Al3+Li+Mg2+
Y+/‐
ZrOPr6O11
Military System Specification with Outdoor Exposure TestingCorrosion Community Seeking Improvements to Corrosion Resistance Performance Prediction
Distribution A: Approved for public release: Distribution Unlimited. 88ABW‐2019‐4680, 25 Sep 2019
Path Forward to Non-Chromium Coatings
Goal is Cr Replacement
Standard Polyurethane TopcoatNon‐Chromium Pigmented Epoxy Primer
Standard or Altenrate Cr‐Free Pretreatment
Aerospace Aluminum Substrate
Non-Cr = Elements that are not Cr
BaSO4
Cr3+Al3+Li+Mg2+
Y+/‐
ZrOPr6O11
New Technology + Qualification + Authorization = Transition
MIL‐PRF‐32239
QPL‐32239
6 Systems
Distribution A: Approved for public release: Distribution Unlimited. 88ABW‐2019‐4680, 25 Sep 2019
Summary• BLUF: Hexavalent Chromium Issue ---- Well Understood• Hierarchy of Controls ---- Replacement• Non-Cr Coatings Are ---- Everything that isn’t Cr• Salt Spray Conundrum ---- Acceleration does not always give the right answer• Path Forward ---- Military System Specification
Distribution A: Approved for public release: Distribution Unlimited. 88ABW‐2019‐4680, 25 Sep 2019
Questions?