Transcript Slide 1

Aluminum Coatings Applied by the
Cold Spray Process for the Repair
of Marine Grade Aluminum
Sponsor:
Dr. Airan Perez, ONR 333
Primary Investigator:
Ben Bouffard, NSWCCD Code 614
Distribution A – Approved for Public Release
Outline
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Project Purpose
Sensitization
Powder Down-Selection
Al-Al2O3 Coating Analysis
Mechanical Properties of Coating
Summary
Project Purpose
• AA5456 in fleet is prone to sensitization and cracking
• Talks with NAVSEA and TWH’s reveal that ships often crack,
but immediate permanent repair is not possible
• Need temporary solution that will ‘keep the water out’ until
next scheduled availability
• Currently use composite patch, which is not ideal:
– Needs to be implemented by highly skilled workforce
– Experiences adhesion problems in extreme UV
environments
– Fire spread issues
• Cold Spray has well documented success in the DOD for
dimensional repair of aluminum and magnesium components
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• This project aims to repair cracks through material
Sensitization
• AA5xxx is
supersaturated with
Mg
• At temperatures
above 65ºC Mg
migrates out of
solution and forms
beta phase (Al2Mg3)
along grain
boundaries
• Beta phase is anodic
to substrate, can lead
to IGSCC
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Powder Down-Selection
• Initially 3 powders procured for testing:
– Commercially pure Al
– Aluminum-Alumina mixture
– AA5456
• Low pressure cold spray system being used has
maximum temperature of 400 ˚C and pressure of 175
psi.
• Commercially pure Al and AA5456 have not
deposited well with these parameters
• Aluminum-Alumina coating deposits extremely wellwill be focus of this presentation
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Al-Al2O3 Coating Analysis
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Sensitized vs Unsensitized
Substrate
Al-Al2O3 Coating
Al2O3 Particle
Unsensitized Substrate
Al-Al2O3 Coating
Al2O3 Particle
Sensitized Substrate 7
Pressure:
Temperature:
Standoff Distance:
Gun Transverse Speed:
Gas Feed Rate:
Thickness:
150
psi
400
˚C
25
mm
30 mm/sec
30 % of max
0.056 inches
Both interfaces show:
• Large Al2O3 particles within coating and
embedded into substrate
• Coating particles result in a large deformation
front (~20 um) within the substrate.
Both coatings show:
•CP-Al particles seem to deform around Al2O3
particles
• Even distribution of Al and Al2O3
• Low porosity observed within coating
EDS Results
Al
O
Ti
Substrate
Al, O, Ti
Coating
• Majority of coating is comprised of aluminum & oxygen
• Argon is present (used to atomize powder)
• Titanium is present in coating
-Separate EDS analysis showed titanium present in original
powder
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Hardness
120
unsensitized
sensitized
Hardness (HV)
100
S1
S2
80
S3
U1
U2
60
U3
Sprayed Material
40
0
500
Base Material
1000
1500
Distance (um)
2000
2500
EBSD Analysis
•Alumina shows little
deformation or change
CP-Al
Particles in general powder
morphology
Al2O3
Particle
•Trend of large grains in
center of particle and
smaller grains along
Interfacial bonding and microstructural evolution
of Al in
outside
ofkinetic
particle
Kang, K.; Wang, J; Bae, G; Ha, S; Lee, C.
spraying. Journal of materials Science 47 (2012)4649-4659.
Al2O3
Particle
•Smaller interparticle
boundaries are created
CP-Al
during the severe strain
Particles localization resultant of
spray process, which
suggests this results in
localized dynamic
recrystallization
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TEM of Single Particle Splat
•Image taken using
selected area
aperture to highlight
dislocations
•Triple point
intersection of grains
•Many dislocations
visible, expect to see
larger dislocation
density along edge of
particle
Potentiodynamic Curves
High Epitt Potential
Large Passivation
Region
Large
difference in
OCP
Shows need
for further
galvanic study
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Salt Fog Testing
• 1500 hours of B117 salt fog testing complete on Al-Al2O3
and AA5456 coatings
• AA5456 is showing pitting in coating, no damage around
scribe
• Al-Al2O3 shows no pitting or corrosion in coating and no
damage around scribe
AA5456 Coating over
Al-Al2O3 Coating over
Al-Al2O3 Coating over
Sensitized Al
Sensitized Al
unsensitized Al
Representative original photos of select B117 panels
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Salt Fog Testing
• Scribe panels show overall corrosion resistance, but in practice
cold spray repair will be small area compared to substrate
• Made mock crack repair plates to test in ASTM B117
• Use 0.25” and 0.5” width mock crack repairs in 4”x6” plates
7/21/2015
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Salt Fog Testing
Al2O3
Coating
Initial
50 hour
350 hour
Al2O3-AA5456
Couple
7/21/2015
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Salt Fog Testing
600 hour
950 hour
• Minor pitting in
Cold Spray material initiated
at 350
hours (Pit diameter of about 10 microns)
Al2O3
Coating
• Pit density of cold spray is more severe than that
observed in AA5xxx
• Pitting in 5xxx coalesces as intergranular corrosion
Al2Obegins
3-AA5456
Couple
• No accelerated pitting in Cold Spray due to couple
with AA5456
7/21/2015
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Al-Al2O3 Mechanical Properties
7/21/2015
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Al2O3 Adhesion Properties
ASTM C633 Adhesion CPAl-Al2O3
Avg Adhesion
Majority of
Std Dev
Value
(ksi)
Failure Modes
Specimen
Sensitized
Handheld
Sensitized
Robot
Unsensitized
Handheld
Unsensitized
Robot
8.06
0.98
Adhesive
7.89
2.28
Adhesive
7.83
n/a
Adhesive
4.60
3.24
Coating
7/21/2015
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• Tensile specimens
machined out of bulk build
• Initial gauge diameters
~0.25 in
Transverse
Tensile Tests-All Cold Spray
Longitudinal
• Specimens tested in both
transverse and longitudinal
directions
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Tensile Tests-All Cold Spray
Specimen Test Direction Average UTS (ksi)
st dev
Transverse
10.37
1.28
Longitudinal
7.21
1.45
• Specimens tested in transverse spray direction show
higher UTS than those tested in longitudinal direction
• Speed of robot important to consider, specimens tested
with traversing gun speed of 20 mm/s showed UTS half the
value of specimens tested with gun speed of 10 mm/s
–Important consideration for handheld gun application
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Fractography of Tensile
Specimens-All Cold Spray
• Combination of intergranular and transgranular cracking
• Primarily cleavage fracture, representative of brittle failure
• No preferential fracture at alumina particles
• No failures at interpass regions
Cleavage
Alumina
Flake point
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Tensile Tests– Cold Spray
Repair
• Repaired different mock crack widths varying from 0.1” to 0.5”
• Crack widths similar to nozzle width could not be filled due to jet
stream of process building over cavity (Takana 2010)
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Tensile Tests– Cold Spray
Repair
• Fracture consists of both transgranular and
intergranular cracking
• No preferential fracture at root or AA5456-Al2O3
coating interface
• Fracture cohesive through cold spray repair
7/21/2015
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Summary
• Successful deposition of Al-Al2O3 using low pressure and
air to deposit onto sensitized and unsensitized AA5456
• Metallurgical analysis of Al-Al2O3 shows dense coating
with low porosity and oxide formation, and similar
deposition and interface between coating and sensitized
and non-sensitized samples.
• Samples show an increased hardness at the interface and
severe particle deformation within the coating
• Satisfactorily high (~8-10 ksi) adhesion and UTS values
• Tensile fracture surfaces show combination of
intergranular and transgranular fracture representative of
brittle failure
Acknowledgements
Dr. Airan Perez
Dr. Jennifer Wolk
Caroline Scheck
NISE 219 Funding under
Dr. Jack Templeton
Fred Lancaster
Joseph Christophersen
Wesley Monillas
Back Up Slides
File: NAVAIR Brief
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