1Ames Laboratory-USDOE, Division of Materials Sciences and Engineering, Ames, IA 2Iowa Powder Atomization Technologies, Inc., Ames, IA Support for this work was provided by the Grow Iowa Values Fund (GIVF) and the US Army (ARDEC) and performed at Ames Lab under contract no. DE-AC02-07CH11358
Net Shape Titanium Powder Requirements Net Shape Titanium Processing Titanium Alloy Powder Chemistry: Low Oxygen Morphology: Ti-6Al-4V ELI Spherical spherical powder of <45 m is ideal for all net-shape processing High yield <45µm powder Oxygen (ppm wt%) 2500 2000 1500 1000 500 2.5 nm native oxide (RT) on 20µm powder ASTM F 2885 ELI O 2 content High throughput and simple process 0 Melt Stock Powder Metal Injection Molding Laser Electron Beam Net shape consolidation
Free Fall vs. Close-Coupled Gas Atomization Ti-6Al-4V results D 50 = 200µm %< 45µm (<5%) Low Energy Transfer [1] Representative Fe alloy run 100-150 C superheat High Energy Transfer D 50 = 29µm %< 45µm (>70%) Does NOT currently exist in industry! [1] Heidloff et al. JOM, 2010
Composite Pour Tube Fabrication Sintering of Y 2 O 3 allows for sub-oxidation and sintering of plasma spray splat boundaries (patent pending) 400-1000 rpm Yttria Tung. YSZ Induction and conduction heating of flowing metal to increase melt superheat for closecoupled atomization Yttria Sub-Oxide Yttria Tungsten YSZ Final Part USPTO# s: 6,358,466; 6,425,504
Ti-6Al-4V Pour Tube Trials: Univ. Birmingham Element (wt%) 250 C Superheat ASTM F1472 Ti 89.1 88.75 91.0 Al 6.26 5.5 6.75 V 4.2 3.5 4.5 Y 70ppm 50ppm (max) O 1573ppm 2000ppm (max) N 204ppm 500ppm (max) C 187ppm 1000ppm (max) Wear (μm) 30±31 TEM BFI [1] [1] [1] TEM HAADF superheat [1] [1] Heidloff et al. JOM, 2010
Ames Laboratory Titanium Close-Coupled Atomizer 5 copper crucible with 20 lb. Ti capacity Inductively-heated pour tube Downstream passivation 15 free-fall distance PAM for 4 custom alloy ingot production (MPC)
Composite Pour Tube Operation Without Metal Optical Pyrometer For proper performance, manipulation of: Induction field Material properties Heat transfer Tungsten acts as heat-generating and superheating layer Induction field allows for pre-heating of pour tube to 2000 C prior to metal flow
Composite Pour Tube Performance Composite pour tube hotter than T m of metal allows tube to run completely dry May allow for semicontinuous use if molten metal is available
Initial Atomization: Ti-48Al-2Cr-2Nb Melt stream flow initiation is highly predictable Spray cone from supersonic atomization gas is highly stable Crown formation from limited superheat Real time: 50 ms
Gas Atomized Ti Powder Morphology Dia. <45µm Dia. <45µm Spherical morphology Very few satellites Very low gas entrapment Dia. <45µm
Powder Chemistry Analysis Element ATI Specification Ingot (ATI) Run #1 <45 m Run #2 Cast Run #3 <45 m Ti REM 59.7 58.9 60.3 58.9 Al 32.5-33.5 32.8 33.7 32.3 33.4 Cr 2.4-2.7 2.58 2.5 2.6 2.7 Nb 4.5-5.1 4.8 4.6 4.8 4.7 O (ppm) 400-1300 700 1300 1100 1300 N (ppm) 200 30 47 27 34 C (ppm) 150 30 250* 170* 400* Y (ppm) 50 <5 60* 50 50 Metal Flow Rate (lb/min) -- -- 10 12.5 17 Pour Tube Liner -- -- Y 2 O 3 Sub-Y 2 O 3 Sub-Y 2 O 3
Downstream Passivation and In-situ Alloying Ames Lab mantra: Free-fall chamber is a REACTION chamber containerless very clean metallic surfaces in-situ processing Atomization wide variety of capabilities (O 2, N 2, NF 3, SF 6 ) Stand-off Distance? Heat transfer modeling of droplet cooling profile Passivation USPTO# s: 5,372,629; 5,589,199 20-25 m powder 4.5nm ~4.5nm in-situ coated surface oxide Opened to air with no special handling Demonstrated F-containing coating on -TiAl powder (190 ppmw F), should improve oxidation resistance of consolidated parts
Composite Pour Tube Optimization: Fe-Cr Alloy Atomization Temperature [2] ΔT ~ 150 C Target Temperature Crucible Temperature Fe-Cr alloy in ceramic crucible with accurate melt temperature (1800 C) 2-color optical pyrometer of outlet temperature (1950 C) [2] Rieken et al. MPIF, 2012
Technology Summary and Future Work Induction melting for molten metal supply to composite pour tube Composite pour tube allows for superheating of molten metal and hot inner wall allows for complete emptying of the pour tube Close-coupled gas atomization provides higher yields of <45µm spherical powder In-situ surface alloying allows for simplified powder passivation and/or improved consolidated part properties Optimize close-coupled atomization parameters for titanium Testing of pour tube lifetime (large batch capacity) Modification of current system to enable larger batch production
Acknowledgements Support for this work was provided by the Grow Iowa Values Fund (GIVF) and the US Army (ARDEC) and performed at Ames Lab under contract no. DE-AC02-07CH11358 From Ames Laboratory: Jim Anderegg for Auger Electron Spectroscopy Tyler Slinger Eduard Zahariev Stephanie Choquette Thank You