Aaron Nardi - United Technology Research Center, CT

Report
Structural Cold Spray Aluminum Alloys & Cold
Spray Additive Manufacturing
June 18, 2014
Presenter: Aaron Nardi
UTRC Team: Michael A Klecka, Matthew D Mordasky,
Xuemei Wang, Tim Landry
Portions of this Research were sponsored by the Army Research Laboratories and was accomplished under Cooperative
Agreement Number W911NF-10-2-0094. The views and conclusions contained in this document are those of the authors and
should not be interpreted as representing the official policies, either expressed or implied, of the Army Research Laboratory or
the U.S. Government. The U.S. Government is authorized to reproduce and distribute reprints for government purposes
notwithstanding any copyright notation herein.
PRESENTATION OVERVIEW
• Similarities between cold spray to other metallic bonding processes
• Single particle 3D impact modeling results and interpretation
• Mechanisms driving mechanical properties of cold spray materials
• Comparison between high temperature nitrogen and lower
temperature helium deposits
• Recent development in the mechanical properties of aluminum
• Additive Manufacturing with cold spray
2
SOLID STATE METALLIC BONDING
Adhesive wear
• Adhesion in tribo-contact is when two metallic surfaces come into contact
and create metallic bonds at the asperity level
Wad=Cm(g1 + g2)
Wad= Work of Adhesion
g1= Surface energy material 1
g2= Surface energy material 2
Cm= Compatibility Parameter
• Surface energy affected by surface
condition
• Oxides
• Chemisorbed layers
• Greases
Derived from phase
diagrams of pure metals
3
SOLID STATE METALLIC BONDING
Cold pressure welding
• Cold Pressure Welding uses normal pressure to
plastically deform the interface between two surfaces
• Surface Area Expands
• Fresh metal extrudes through fractures in cover layer
• Fresh metal surfaces bond
Extracted from Metal Construction, 1986, N. Bay, “Cold
Welding Part 1Characteristics bonding mechanisms bond
strength”
Data from Journal of Engineering for Industry,
1979, N. Bay, “Cold Pressure Welding : The
Mechanisms Governing Bonding”
Breakdown of surface films
and cover layer
4
SOLID STATE METALLIC BONDING
Explosive cladding/welding
• Explosive cladding uses an explosive charge to accelerate a “flyer plate” or
material to be bonded toward a substrate
• High levels of plastic flow of material at interface
• Surface layer breakdown and removal through jet formation
• Fresh metal surfaces bond
Similarities in jet formation
Images from ASM Handbook Volume 6, Solid State
Welding Processes, Explosive Welding
5
SOLID STATE METALLIC BONDING
Summary of comparisons
• Materials compatibility enables increased bond strength
• Compatible bond layers
• Encapsulated powders
• Surface contamination requires higher surface expansion (strain) to
achieve bonding
• High plastic strain of both surfaces improves bonding
• Material jetting from interface can eliminate or further breakdown
surface contamination
6
MECHANICAL PROPERTIES OF COLD SPRAY DEPOSITS
Bond strength for buildup applications of dissimilar materials
• Method used to measure bond strength is
lug shear testing
• Spray thick buildup ~0.125 inches thick
• Machine back to create a lug where t >
0.5w and L~2w
• Use vise or fixture to shear lug from
substrate
w
t
Material Couple
Before Process
Development (ksi)
After Process
Development (ksi)
Superalloy on Gray
Cast Iron
5
20-30
Aluminum to
Aluminum
5-8
22
Ta Alloy to 40 HRC
Steel
<5
37
SS to 35 HRC Steel
<10
24-35
Key to Performance
• Selection of interface materials
based on compatibility
• Process development to ensure the
correct physics occurs at the
interface
Result
• High quality metallic bonding
capable of carrying significant
loads
7
EFFECT OF PARTICLE IMPACT VELOCITY
Higher impact velocity increases plastic flow of particle and substrate
• As impacting velocity increases
• Plastic deformation of both particle and substrate 
• Contacting surface area 
Temperature contours
• Particle penetration 
• Temperature raise 
• Flow stress 
(note that Tp0 = 236°c and Ts0= 25°c)
Particle on substrate
Particle
Substrate
V0 = 612 m/s
V0 = 612 m/s
V0 = 612 m/s
V0 = 800 m/s
V0 = 800 m/s
V0 =800 m/s
V0 = 980 m/s
V0 = 980 m/s
V0 = 980 m/s
• Contact pressure 
8
EFFECT OF PRE-HEATING TEMPERATURE
Higher pre-heat temperatures increases particle plastic flow
• As impacting temperature increases
• Plastic deformation of particle 
• Contacting surface area of particle 
• Particle penetration  (slight)
• Temperature raise 
• Flow stress 
Temperature contours (90 impact)
(note that V0 = 612 m/s)
Tp0=25°c
Tp0=127°c
Tp0 = 236°c
Tp0 = 327°c
• Contact pressure – negligible
9
MECHANISMS AFFECTING MECHANICAL PROPERTIES OF COLD
SPRAY DEPOSITS
Mechanisms driving properties of cold sprayed deposits
• Region 1 – Linear elastic
material deformation
• Dominated by consolidated
density of cold spray deposit
• Region 2 – Initial particle
plasticity
• Plastic deformation of particles
begins to open defects
between particles
• Larger defects drive higher
crack tip opening displacement
• Region 3 – Large scale
plasticity
• Any defects in the structure
are exercised due to large
scale plasticity
• Region 4 – strain localization
and defect coalescence
10
MECHANISMS AFFECTING MECHANICAL PROPERTIES OF COLD SPRAY
DEPOSITS
Micro-structural evolution of inter-particle defects
Cut Lines
Starting Microstructure
Defect Opening due
to high plastic strain
Unetched
Etched
Crack extending from
defect
11
MECHANISMS AFFECTING MECHANICAL PROPERTIES OF COLD
SPRAY DEPOSITS
Simulation and test data for helium and nitrogen spray processes
• Model predicts better mechanical interlock & bonding in
helium deposits
• Critical velocity calculations indicating both should
consolidate similarly
Helium Sprayed
CVR = 1.58
Nitrogen Sprayed
CVR=1.45
Deformed shapes
Nitrogen Sprayed
Helium Sprayed
Temperature contours
Dominated by transparticle fracture
Helium sprayed
Fracture surfaces
(dp=40 m ,Tp0 = 236 °c , V0= 980 m/s)
Dominated by interparticle fracture
Substrate
Substrate
Particle
Particle
Nitrogen Sprayed
(dp=40 m ,Tp0 = 427 °c, V0= 635 m/s)
12
MECHANICAL PROPERTIES OF COLD SPRAY DEPOSITS
Aluminum deposits before and after process modifications
• Initial process development often results
in deposits with high strength but low
ductility
• Achieving velocity near critical velocity
• Through process optimization it is
possible to achieve high ductility with
only a moderate effect on ultimate
strength
• Changes in particle velocity, impact
temperature, particle size distribution,
particle morphology, particle metallurgy,
or some combination of these
• Ductility is tied to defects more than
work hardening as originally thought
• Ductility in a cold spray deposit is
therefore a good predictor of the
expected fatigue performance in both
LCF and HCF
13
ADDITIVE MANUFACTURING WITH COLD SPRAY
DEPOSITION
Manufacture of small lightly loaded gears with improved lubricity and wear
• Lightly loaded aerospace gears typically made from nitrided steel
• Fretting, Dithering wear, potential friction concerns
• Alternate approach – Spray form base gear and add wear coating
to tooth surface
• Select base metal for weight, stiffness, thermal conductiltiy, etc. (eg.
steel, aluminum, titanium)
• Select surface deposit for wear, friction, anti-galling, etc. (e.g. Tribaloy
T-800 blend)
Removed from
substrate by
thermal shock
Wear layer added to spray
formed part then finish
machined
Finished Gears
Spray Formed Part
Steel Mandrel
14

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