Material Development for Electron Beam Melting

Timothy Horn Tjhorn.ims@gmail.com Center for Additive Manufacturing and Logistics http://camal.ncsu.edu

• 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

Advantages of Additive Manufacturing

• 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

•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

Center For Additive Manufacturing and Logistics

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

2. Material Properties

3. Powder Properties

1. Feasibility 4. Hardware

Changes

• Toxicity, PPE, Exposure Limits

• X-Ray Generation

• Regulations (ITAR)

• Minimum Ignition Energy

Chronic Beryllium Disease (CBD)

www.adinex.be

Modified Hartmann Tube: Minimum Energy (Joules) from a capacitor discharge to ignite a dust cloud of known density in 1 out of 10 tries

Minimum MIE =0.5J

Electron Beam Melting (ARCAM): Parameter Development Strategy

2. Material Properties

3. Powder Properties

1. Feasibility 4. Hardware

Changes

• Melting Temperature

• Thermal Conductivity

• Electrical Conductivity

• Vapor Pressures

• Phase Diagrams

• TTT Diagrams

• Known Heat Treatments

• Oxidation/Contamination

Electron Beam Melting (ARCAM): Parameter Development Strategy

2. Material Properties

3. Powder Properties

1. Feasibility 4. Hardware

Changes

• Powder Morphology • Powder Flow

• Internal Porosity

• Apparent Density

• Powder Size Distribution

• Sintering Characteristics

Type

Average Volumetric Flow Rate

(cm3/s)

Powder A 0.599

Powder B 0.704

Powder C 0.699

C

•Apparent Density

•Size

•Shape

•Surface

Contamination

99.99% Cu

99.99% Cu

99.80% Cu

ASTM B855-06

Flow rate is a good indicator of

powder raking, packing, feeding

characteristics!

$$$

$$$

$$$

$

0.0%

10.0%

20.0%

30.0%

40.0%

50.0%

60.0%

<60 60-100 100-220 220-500

Size Range (microns)

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ht)

Electron Beam Melting (ARCAM): Parameter Development Strategy

2. Material Properties

3. Powder Properties

1. Feasibility 4. Hardware

Changes

• Powder Morphology • Powder Flow

• Internal Porosity

• Apparent Density

• Powder Size Distribution

• Sintering Characteristics

New Reuse

Electron Beam Melting (ARCAM): Parameter Development Strategy

2. Material Properties

3. Powder Properties

1. Feasibility 4. Hardware

Changes

• Powder Quantity

• Raking characteristics

• Thermal considerations

Electron Beam Melting (ARCAM): Parameter Development Strategy

2. Material Properties

3. Powder Properties

1. Feasibility 4. Hardware

Changes

• Powder Quantity

• Raking characteristics

• Thermal considerations

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

2

3 Line Offset

Line Order

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

P=Beam power (50-4000 W)

V=spot velocity (10-20000 mm/s)

e-

d=spot size (0.1-0.4 mm)

T=Working temperature (750C)

e-

e-

e-

e- Melt area

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)

cdv

PZ

m 1.0

UIE

dv

Electron Beam Melting (ARCAM): Parameter Development Strategy

Melting Parameters: Hatch

Porosity

Secondary Parameter Search: •Contour Parameters •Hatch Settings •Temperature Stability •Turning Point Function •Thickness Function

Melt pool quality continually observed

by operator!

Repeat this process until melt is satisfactory

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

Two medium-beta SNS cryomodules in assembly at JLab

Field Probe

Ti Bellows

NbTi Dished Head

Stiffening Rings

2-Phase Return Header NbTi

Dished Head

HOM Coupler

Fundamental Power Coupler

HOM Coupler

Medium Beta Cavity

•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

Pressure Monitored by RGA

•Stanford Research Systems

•Quadrupole mass

spectrometer sensor

•Upstream particle filters

•Small Quantity of Powder •Very High Temperature: 2477 °C

Average RRR Average Tc Average ΔTc

Sample A 18 9.19 0.09

Sample B 19 9.16 0.12

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

Increasing Beam Current

<24°C = Martensitic 37°C= Austenitic

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 pre-alloyed 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

Jump safe

Melt 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

• 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 Ti-6Al-4V Ti-6Al-4V

Ti-6Al-4V-1B

We would like to thank ATI for developing and providing the Ti-6Al-4V +B powder used in these tests!

Electron Beam Melting (ARCAM): Ti-6Al-4V B

No Boron 0.25% Boron 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