Material Development for Electron Beam Melting Timothy Horn Tjhorn.ims@gmail.com 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 3. Powder Properties 4. Hardware Changes Toxicity, PPE, Exposure Limits X-Ray Generation Regulations (ITAR) Chronic Beryllium Disease (CBD) Minimum Ignition Energy 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 www.adinex.be
Electron Beam Melting (ARCAM): Parameter Development Strategy 1. Feasibility 2. Material Properties 3. Powder Properties 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 1. Feasibility 2. Material Properties 3. Powder Properties 4. Hardware Changes Powder Morphology Powder Flow Internal Porosity Apparent Density Powder Size Distribution Sintering Characteristics ASTM B855-06 Flow rate is a good indicator of powder raking, packing, feeding characteristics! 99.99% Cu $$$ 99.99% Cu $$$ $$$ 99.80% Cu $ Type Average Volumetric Flow Rate (cm 3 /s) Powder A 0.599 Powder B 0.704 Powder C 0.699 Apparent Density Size Shape Surface Contamination
Electron Beam Melting (ARCAM): Parameter Development Strategy Percentage (by weight) 1. Feasibility 2. Material Properties 3. Powder Properties 4. Hardware Changes Powder Morphology 60.0% 50.0% Powder Flow Internal Porosity 40.0% 30.0% 20.0% Apparent Density Powder Size Distribution 10.0% 0.0% <60 60-100 100-220 220-500 Size Range (microns) Sintering Characteristics New Reuse
Electron Beam Melting (ARCAM): Parameter Development Strategy 1. Feasibility 2. Material Properties 3. Powder Properties 4. Hardware Changes Powder Quantity Raking characteristics Thermal considerations
Electron Beam Melting (ARCAM): Parameter Development Strategy 1. Feasibility 2. Material Properties 3. Powder Properties 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 Line Order Line Offset 3
Electron Beam Melting (ARCAM): Parameter Development Strategy Melting Parameters: Hatch Initial Parameter Search: Beam Speed Beam Power Beam Focus Curling/delaminating V=spot velocity (10-20000 mm/s) e - e - e - e - e - d=spot size (0.1-0.4 mm) P=Beam power (50-4000 W) Melt area Beam Speed (mm/s) 400, 800, 1500, 2000 Beam Current (ma) 8-20 Speed Function* T=Working temperature (750C) Z 0.1 m P dv c Z = melt depth (mm) P = beam power (W) θ m = 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) UI E dv
Electron Beam Melting (ARCAM): Parameter Development Strategy Melting Parameters: Hatch Melt pool quality continually observed by operator! Secondary Parameter Search: Contour Parameters Hatch Settings Temperature Stability Turning Point Function Thickness Function Porosity 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 NbTi Dished Head Field Probe Ti Bellows Stiffening Rings 2-Phase Return Header NbTi Dished Head HOM Coupler HOM Coupler Medium Beta Cavity 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 Average RRR Average T c Average ΔT c 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. Stanford Research Systems Quadrupole mass spectrometer sensor Upstream particle filters
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 ~40 Layers Melt safe Jump safe Could Boron additions help control microstructure in EBM produced Ti-64?
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 Ti- 6Al-4V Ti-6Al-4V Ti-6Al-4V-1B No Boron 0.25% Boron 1.0% Boron We would like to thank ATI for developing and providing the Ti-6Al-4V +B powder used in these tests!
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