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Material Development for Electron
Beam Melting
Timothy Horn
[email protected]
Center for Additive Manufacturing and Logistics
http://camal.ncsu.edu
Advantages of Additive Manufacturing
•
Extremely complex geometries not possible with
traditional methods (geometric lattice structures,
conformal channels )
•
Structurally optimized components-unique properties
(thermal, electrical, biological etc.)
•
Material is only used where it is needed
•
Significant reductions in buy-to-fly ratio
•
Significant savings in fuel
•
No tooling or dies needed to fabricate a part
= short runs, small batches, legacy parts
•
Point of use process - reduced inventory -reduced
carrying and transport costs
•
Combine assemblies into single parts
•
Opportunities for materials development
Advantages of Additive Manufacturing
•
Extremely complex geometries not possible with
traditional methods (geometric lattice structures,
conformal channels )
•
Structurally optimized components-unique properties
(thermal, electrical, biological etc.)
•
•
•
Material is only used where it is needed
•
Significant reductions in buy-to-fly ratio
•
Significant savings in fuel
No tooling or dies needed to fabricate a part
= short runs, small batches, legacy parts
Point of use process - reduced inventory -reduced
carrying and transport costs
•
Combine assemblies into single parts
•
Opportunities for materials development
•
•
•
•
•
•
•
GRCop-84
OFE Copper
Niobium
C103 Niobium
Beryllium Alloys
Ti-Al
Nickel Alloys (625,
718, M247)
•
•
•
•
•
•
Tool Steels
Aluminum Alloys
(6061, 7075, 2024)
Nitinol (55%, 60%)
Ti6Al4VB
Metal Matrix
Composites
Lunar Regolith
Center For Additive Manufacturing and Logistics
•Over 20 faculty members from multiple disciplines
•20+ graduate students
•Plastic based additive technologies
•(FDM,SLA, polyjet, powder consolidation)
•Clean room facility houses bio-plotter
•Direct metal additive fabrication research
Current Research Areas Include:
• Structural Optimization
• Biomedical applications/custom implants
• New materials development, parameter optimization, process
mapping
• Energy absorption/attenuation, negative Poisson structures
• Fatigue/creep and other mechanical properties (characterization)
• Surface finish/powder removal/residual stresses
• Machining of components to specified tolerances
• Supply chain and Logistics of additive networks
Electron Beam Melting (ARCAM)
•
4kW Electron beam is generated within
the electron beam gun
•
The tungsten filament is heated at
extremely high temperatures which
releases electrons
•
Electrons accelerate with an electrical
field and are focused by electromagnetic
coils
•
The electron beam melts each layer of
metal powder to the desired geometry
•
Vacuum/melt process eliminates
impurities and yields high strength
properties of the material
•
Vacuum also facilitates the use of highly
reactive metals
•
High build temperature provides good
form stability and low residual stress in
the part
•
20-200 micron layer thickness
•
20-300 micron powder
Electron Beam Melting (ARCAM)
•
Energy Balance –Maintain constant build
temperature
•
Preheat 1: Lightly sinter the powder
“Jump Safe”
•
Preheat 2: Increased local sintering “Melt
Safe”
•
Wafer Supports
•
Contours
•
Hatch
•
Heating Steps
Electron Beam Melting (ARCAM): Parameter Development Strategy
1. Feasibility
2. Material
Properties
•
Toxicity, PPE, Exposure Limits
•
X-Ray Generation
•
Regulations (ITAR)
•
Minimum Ignition Energy
3. Powder
Properties
4. Hardware
Changes
Chronic
Beryllium
Disease
(CBD)
Modified Hartmann
Tube:
Minimum Energy
(Joules) from a
capacitor discharge to
ignite a dust cloud of
known density in 1
out of 10 tries
www.adinex.be
Minimum MIE =0.5J
Electron Beam Melting (ARCAM): Parameter Development Strategy
1. Feasibility
•
Melting Temperature
•
Thermal Conductivity
•
Electrical Conductivity
•
Vapor Pressures
•
Phase Diagrams
•
TTT Diagrams
•
Known Heat Treatments
•
Oxidation/Contamination
2. Material
Properties
3. Powder
Properties
4. Hardware
Changes
Electron Beam Melting (ARCAM): Parameter Development Strategy
1. Feasibility
•
2. Material
Properties
Powder Flow
•
Internal Porosity
•
Apparent Density
•
Powder Size Distribution
•
Sintering Characteristics
4. Hardware
Changes
99.99% Cu
Powder Morphology
•
3. Powder
Properties
$$$
ASTM B855-06
99.99% Cu
Type
Average
Volumetric
Flow Rate
(cm3/s)
Powder A
0.599
Powder B
0.704
Powder C
0.699
$$$
$$$
•Apparent Density
99.80% Cu
$
Flow rate is a good indicator of
powder raking, packing, feeding
characteristics!
•Size
•Shape
•Surface
Contamination
Electron Beam Melting (ARCAM): Parameter Development Strategy
•
Powder Morphology
•
Powder Flow
•
Internal Porosity
•
Apparent Density
•
Powder Size Distribution
•
Sintering Characteristics
2. Material
Properties
3. Powder
Properties
4. Hardware
Changes
60.0%
Percentage (by weight)
1. Feasibility
50.0%
40.0%
30.0%
20.0%
10.0%
0.0%
<60
60-100
100-220 220-500
Size Range (microns)
New
Reuse
Electron Beam Melting (ARCAM): Parameter Development Strategy
1. Feasibility
•
Powder Quantity
•
Raking characteristics
•
Thermal considerations
2. Material
Properties
3. Powder
Properties
4. Hardware
Changes
Electron Beam Melting (ARCAM): Parameter Development Strategy
1. Feasibility
•
Powder Quantity
•
Raking characteristics
•
Thermal considerations
2. Material
Properties
3. Powder
Properties
4. Hardware
Changes
Electron Beam Melting (ARCAM): Parameter Development Strategy
Preheating Parameters: Smoke Test
•
Beam Focus Offset (mA)
•
Line Offset (mm)
•
Line Order
•
Beam Current (min, average,
ramping) (mA)
•
Beam Speed (mm/s)
•
Box Size
•
Average Current
•
Number of Reps
1
Line Order
2
Line Offset
3
Electron Beam Melting (ARCAM): Parameter Development Strategy
Melting Parameters: Hatch
Initial Parameter Search:
•Beam Speed
•Beam Power
•Beam Focus
Beam Speed (mm/s)
400, 800, 1500, 2000
Beam Current (mA)
8-20
Speed Function*
Curling/delaminating
V=spot velocity (10-20000 mm/s)
d=spot size (0.1-0.4 mm)
e-
e-
ee-
e-
P=Beam power (50-4000 W)
Melt area
T=Working temperature (750C)
Z  0.1
P
 m dvc 
Z = melt depth (mm)
P = beam power (W)
θm = temperature rise to melting point (C)
κ = thermal conductivity (W/mm- C)
d = beam diameter (mm)
v = beam velocity (mm/sec)
ρ = density (gm/mm^3)
c = specific heat (J/gm- C)
E
UI
dv
Electron Beam Melting (ARCAM): Parameter Development Strategy
Melting Parameters: Hatch
Melt pool
quality continually observed
by operator!
Porosity
Repeat this process until melt is satisfactory
Secondary Parameter
Search:
•Contour Parameters
•Hatch Settings
•Temperature Stability
•Turning Point Function
•Thickness Function
Electron Beam Melting (ARCAM): Parameter Development Strategy
Melting Parameters: Testing/Validation
•Thermal Conductivity:
390.5 W/m·K
•Electrical Conductivity:
(72 to 79 % IACS for
cathode)
•Field Testing: Verified
performance under high
power RF conditions
Electron Beam Melting (ARCAM): Applications-High Purity Copper
•High average power Normal Conducting Radio Frequency (NCRF)
photoinjectors.
•Accelerators for high-energy electron-beam applications
• Requires 99.99% pure copper
• (Conductivity >100% IACS ~5.8 x10^7 S/m )
•A key problem limiting the duty cycle of NCRF photoinjectors is
inefficient cooling
Electron Beam Melting (ARCAM): Applications-High Purity Niobium
NbTi
Dished
Head
Ti
Bellows
Field
Probe
HOM
Coupler
Medium
Beta Cavity
Stiffening
Rings
2-Phase Return
Header
NbTi
Dished
Head
HOM
Coupler
Fundamental
Power
Coupler
Two medium-beta SNS cryomodules in assembly at JLab
•Superconducting Radio Frequency (SRF) Accelerators are now considered the device of choice for many applications in high energy and
nuclear physics. - Energy Recovery Linacs (ERLs) Linear Colliders (ILC) Neutrino Factories Spallation Neutron Sources.
•After the Accelerating Cavity, the Fundimental Power Coupler (FPC) is considered the most important component in the SRF accelerator.
- The FPC transfers power from the RF source to the accelerating cavity
•Vacuum, Cryogenic, and High Power Electromagnetic Environment
•Must also dissapate hundreds of kW of average power
Electron Beam Melting (ARCAM): Applications-High Purity Niobium
•Small Quantity of Powder
•Very High Temperature: 2477 °C
Pressure Monitored by RGA
Sample A
Sample B
Average RRR
Average Tc
Average ΔTc
18
19
9.19
9.16
0.09
0.12
•Stanford Research Systems
•Quadrupole mass
spectrometer sensor
•Upstream particle filters
Samples are superconducting:
•
RRR values ~ ½ of reactor grade bulk material.
•
Transition temperatures are ~ 0.11 K below bulk value.
•
Sample B has a slightly lower Tc on average than sample A
•
Transition Width (ΔTc) is consistent with other measured bulk
samples
•
Sample A has clean transitions for all four samples measured.
•
Sample B has a two step transition for the two samples
measured.
Electron Beam Melting (ARCAM): Applications-Aluminum & Alloys
Electron Beam Melting (ARCAM): Nitinol Ni-Ti
<24°C = Martensitic
37°C= Austenitic
Increasing Beam Current
Electron Beam Melting (ARCAM): GRCop-84
Mahale, Cormier
Electron Beam Melting (ARCAM): GRCop-84
Mahale, Cormier
Electron Beam Melting (ARCAM): Titanium Aluminide
•
2004: Development of Process
parameters for pre-alloyed powders
•
2005: Investigation into Combustion
Syntesis
•
2009: Development of new prealloyed parameter set
•
2013: High Niobium Ti-Al- Mercury
Center
Electron Beam Melting (ARCAM): Ti-6Al-4V B
• One of the key problems with EBM fabrication of
Ti-6Al-4V is the large columnar β grain growth
Melt safe
Jump safe
• Could Boron additions help control microstructure in
EBM produced Ti-64?
~40
Layers
Electron Beam Melting (ARCAM): Ti-6Al-4V B
•
Initial experiments conducted in 2006 (Denis
Cormier, Tushar Mahale)
•
TiB2 mixed mechanically combined with
Arcam Ti-6Al-4V powder in an attempt to
refine or disrupt the columnar
microstructure of EBM fabricated parts
•
TiB2 did not go into solution
•
Resulted in relatively poor mechanical
properties
•
Searched for a source of pre-alloyed powder
Electron Beam Melting (ARCAM): Ti-6Al-4V B
•
In 2012 ATI was able to provide us with pre-alloyed
Ti-6Al-4V with trace amounts of Boron.
•
The Ti-6Al-4V powder shows a typical lath structure,
the Ti-6Al-4V-1B powder has a homogenous structure
that exhibits dendritic patterns.
•
Properties of Ti-6Al-4V and Ti-6Al-4V-1B samples
fabricated with the Arcam Electron Beam Melting
process using the available process parameters for Ti6Al-4V
Ti-6Al-4V
Ti-6Al-4V-1B
No Boron
0.25% Boron
We would like to thank ATI for developing
and providing the Ti-6Al-4V +B powder
used in these tests!
1.0% Boron
Future:
• Improve/design new and existing
materials for additive manufacturing
• Develop predictive models for process
parameters
• Development in process monitoring
technologies
Acknowlegements:
Dr. Denis Cormier
Dr. Tushar Mahale
Dr. Ola Harrysson
Dr. Harvey West
Pedro Frigola
Kyle Knowlson
Dr. Andrzej Wojcieszynski
Jean Stewart