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1
Laboratory Testing to Identify Permanent
PVD Coatings to Minimize Lubricant Use
During Forging
T. Kehe, S. Midson, A. Korenyi-Both,
K.D. Clarke
Forging Technical Conference,
Sept. 11, 2018, Long Beach, CA.
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Project Goals
• Utilize permanent PVD thin-film coatings
Apply to forging dies
Minimize friction coefficient
Reduce use of lubricants
Reduce lubricant overspray
Improve die life
Improve cycle times
Improve quality of forgings
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• Leverage the recent CSM “Lube Free” die casting
die coating project
New PVD coatings reduced lubricant use significantly
Apply similar coating technologies to forging dies
• Develop a flexible testing methodology
Evaluate relative friction coefficients of PVD surface
coatings during aluminum forging (die temperatures
<400°C)
33
Project Approach
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Project Tasks
1. Perform literature review of coatings used in
forging and metals fabrication
2. Design and fabricate tooling for laboratory
forging test
3. Set up laboratory testing procedure and procure
coated die test samples
4. Perform plant trial of best PVD coating
identified during laboratory testing
5. Reporting
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Today
• Literature review of PVD coatings
• Die design and fabrication
• Validation of friction testing procedures
and initial friction test results
• PVD coating test matrix
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Literature review of PVD coatings
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Literature review of PVD coatings
•Coating thickness is typically <10 m
Thicker coatings will spall
•Substrate temperature needs to be less than 550°C (1,000°F) during application
To avoid over-tempering of hardened tool-steel substrate
•PVD coating meets these criteria
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Literature review of PVD coatings
• PVD coatings are not common on forging dies
More common on die casting dies
• Most studies focused on wear resistance and die life
Not on improving lubricity
• Coatings examined include: CrN, TiN, TiC, TiCN, TiAlCN, AlCrN, TiAlN
• Data from Leskovsek et al. showed that TiCN did reduce coefficient of friction
Source: Leskovsek et al., Wear, 2009
H11 plasma nitrided, PECVD
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Literature review of PVD coatings
Several hard coatings have
the potential for improving
lubricity• Diamond like carbon (DLC)
• CrN/SiC
• TiCN
Sources: Mulligan et al., Mat. & Man. Proc., 2014
Donnet and Erdemir, 2008
CoatingCoefficient of
Friction
CrN 0.28
CrN/DLC 0.07
CrN/SiC 0.07
Cutting applications
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Literature review of PVD coatings
MoS2 is an excellent lubricant
• Due to its layered structure
MoS2 can be directly deposited
• Deposited structures are very soft
• Easily detach from substrate
MoS2 has been deposited as part
of a harder coating
• Titanium
• AlCrN
• Coefficient of friction values were
reducedSource: Bobzin et al., Ad. Eng. Mat., 2016
Cold-forging
(a) Uncoated substrate (M2)
(b), (c) & (d) utilizing (Cr1-XAlX)N/
MoYSZ-type coatings
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Literature review of PVD coatings
For applications at high
temperatures
• Unreasonable to expect
materials to resist
oxidation for long periods
Utilize oxide materials
with low interfacial shear
strengths
• V2O5
• MoO3
• Layered structure of V2O5
• V atoms as grey balls
• O atoms as red balls
Source: Mulligan et al., Surf. & Coat. Tech., 2010
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PVD coatingsType of Coating Specifics Supplier Temperature
Single-layer hard
coatingsTiCN
Tribologix, Dayton,
Ionbond<400°C
Multi-layer hard
coatings
Super MoS2 Tribologix 375°C
Ti-MoS2 (MOST) Teer in UK, Ionbond <350°C
AlCrN-MoS2 Tribologix
TiCN-TiMoS2 Teer
CrN-DLC Phygen <300°C
CrN-SiC Phygen
i-Kote Tribologix 350°C
Noble MetalsHard coating plus noble
metal
Voevodin, Scharf &
Samir at UNT<500°C
Highly lubricious
oxide-- None identified
Plasma Sprayed PS400 NASA
Laser Textured Laser texture a TiCN coating Tribologix/CSM
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Test methodologies and die design
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Test methodologies and die design
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Test methodologies and die design
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Test methodologies and die design
• Easy installation and removal
• Trials of multiple coatings
• Ability to quickly switch die faces
• Room temperature to ~500°C capability
• Fit on available 100 kip hydraulic press
• Measure load and displacement
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Test methodologies and die design
Design tooling with
removable inserts
• In-house surface
preparation of
uncoated die sets
• Coat smaller pieces
• Send sets of tooling
to various vendors
for coating
• Allow for elevated
temperature testing
• Easily replaceable• Aluminum ring 1” OD, ½” ID
• 0.2 in/s compression velocity
• Applied to a 100 kip force
Effective stress, ksi
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Test methodologies and die design
25 mm
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Test methodologies and die design
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2020
Validation of friction testing procedures and
initial friction test results
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Friction testing results: 6061 Al @ RT
Left to right: Increasing reductions in height
Top to bottom: Increasingly effective lubricants
No lubricant
MoS2 grease
Dry graphite
spray
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Fri
ctio
n c
oeffic
ient
Test number
Friction testing results• Die inserts ground to 1200 grit and polished from 6μm to
3μm to 1μm
• Friction coefficient responds to multiple tests
• Surface conditioning performed on dies
• No lubricant, room temperature
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Friction testing results – lubricant amountD
ecre
ase in insid
e d
iam
ete
r
% height reductionFriction factor
No Lubricant
CRC Graphite
Molykote MoS2
0.8 0.3
0.12
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Friction testing resultsD
ecre
ase in insid
e d
iam
ete
r
% height reductionFriction factor
No Lubricant
CRC Graphite
Molykote MoS2
0.8 0.3
0.12
No lube, 200°C
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2525
PVD Coating Test Matrix
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6 die sets (uppers + lowers)
• 1 H13 set used for no-coating baseline
• 4 H13 sets are at vendors for coating• Can be re-coated
• Surface imaging, tribology, and metallographic
examination of coating performance also possible
• 1 W303 set will be used to validate no-
coating baseline values and coating
effectiveness on a different substrate
PVD coating test matrix
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Type of Coating Specifics Supplier Temperature
Single-layer hard
coatingsTiCN
Tribologix, Dayton,
Ionbond<400°C
Multi-layer hard
coatings
Super MoS2 Tribologix 375°C
Ti-MoS2 (MOST) Teer in UK, Ionbond <350°C
AlCrN-MoS2 Tribologix
TiCN-TiMoS2 Teer
CrN-DLC Phygen <300°C
CrN-SiC Phygen
i-Kote Tribologix 350°C
Noble MetalsHard coating plus noble
metal
Voevodin, Scharf &
Samir at UNT<500°C
Highly lubricious
oxide-- None identified
Plasma Sprayed PS400 NASA
Laser Textured Laser texture a TiCN coating Tribologix/CSM
PVD coating test matrix
✅
✅
✅
✅
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PVD coating test matrix
• Friction testing on uncoated dies and four initial
PVD coatings selected (5)
• Temperature will be varied from RT to 300°C (4)
• Tests will be performed with and without
lubricant…MoS2 and Graphite (3)
• Three sets of rings at three deformation levels (9)
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Summary
• Flexible forging tooling has been designed and built
• Room temperature to 500°C
• Loads up to 100 kip
• 6 sets of interchangeable die inserts
• Ring-compression friction tests have been validated
• Polished as-heat treated (uncoated) dies
• Room temperature to 300°C
• Forging die coatings
• Literature review complete
• List of promising coatings compiled
• Four initial coatings selected for application to dies (underway)
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Acknowledgements
• FIERF – stage gated grant, “Laboratory Testing to
Identify Permanent PVD Coatings to Minimize
Lubricants Use During Forging”
• FIERF board – stage gate reviews and guidance
• NSF REU program grant through the Center for
Advanced Non-Ferrous Structural Alloys
• CSM undergraduate research support
• Die materials
• Bohler-Uddeholm (Patricia Miller), H13 and W303 inserts
• Hitachi (Tom Bell), H13 inserts
• Finkl (Al Underys), 4340 die blocks
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Test methodologies and die design
Trevor Kehe
• Currently a senior at CSM
• Pursuing a degree in metallurgical and materials engineering
• Started on Forging Coatings project in August, 2017
• Designed die sets
• Oversaw manufacturing/machining
• Initiated testing program
• Interested in pursuing a graduate degree at CSM
• Interests
• Mines Baseball
• 2017: 1 out away from CWS
• 2018: 2nd in RMAC
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Thank you!
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Literature review of PVD coatings
Mechanism Material Examples Temp. Range
Traditional liquid lubricants Oils and greases <~250°C
Atomic structures that can
easily shearMoS2, graphite <300°C
PVD hard coatings
(can contain softer lubricating
phases)
Diamond like carbon,
TiCN, CrN/SiC, i-Kote
<300-500°C
depending upon
coating
Soft metals within hard
coatings that diffuse to
contact surfaces
Ag, Au, Cu encapsulated
in TiN, CrN, VN, YSZ,
CrAlN
300 – 500°C
Lubricious oxides V2O5, MoO3 500 – 1000°C
Source: Adapted from Voevodin et al., Surf. & Coat. Tech., 2014
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Friction testing results: 6061 Al @ RT
Lubricant application conditions – did not affect room
temperature friction factor
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Friction testing results: 6061 Al @ RT
Left to right: Increasing reductions in height
No lubricant
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Literature review of PVD coatings
PS400• Nickel-molybdenum
binder for strength
• Silver and barium–calcium fluoride are added for lubrication
Layered microstructure
Source: DellaCorte & Edmonds, NASA Report, 2009
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Literature review of PVD coatings
• Ag-Ta-O
• Sputtered from Ta
and Ag targets in
reactive oxygen
atmosphere
• Exhibit extremely low
coefficient of friction
at 600 – 700°C CoF for four silver tantalate
coatingsSource: Stone et al., Surf. & Coat. Tech., 2013
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Friction testing results
• Identification of lubricants to be used for further tests
(Graphite, MoS2)
• Four trials run at three different deformation amounts for
each condition
• At max load, a greater % deformation is achieved with
lubrication
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Literature review of PVD coatings
Noble metals are dispersed
in hard coatings
• Ag in CrN
• Ag in CrAlN
• Ag in TiC
Noble metal diffuses to
surface
• Provide lubricity at
temperature greater than
300oC
Source: Voevodin et al., Surf. & Coat. Tech., 2014
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Test methodologies and die design
• Cooling of dies during test set up recorded
• Heat higher than target test temperature
• Test is run when goal temperature is reached
• Al samples reach same temperature as dies quickly
50
100
150
200
250
300
0 50 100 150 200 250 300
Tem
p (˚C
)
Time (sec)
160 ˚C
230 ˚C
300˚C
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Literature review of PVD coatings
Traditional Surface TreatmentsHard Thin-Film Coatings
Weld Overlay