Computational Design of Precipitate Strengthened Co-Base Alloy James Saal, PhD QuesTek Innovations This project is a collective effort of the QuesTek technology group. p. 1
Outline Background SERDP Design Prototype and Characterization Scale up and Properties CHiMaD Database update Strength modeling Two-step temper p. 2
Technical Background A high-strength, wear-resistant material alternative to CuBe is sought for highly loaded, unlubricated aerospace bushing applications to avoid health-hazards associated with Be. Key property goals are WEAR resistance and STRENGTH Low-friction bushing applications Achieve strength in large product sizes without cold work (Quench suppressibility) Vertical Tail Hinge Assembly Wing Lug Attach Main Landing Gear Objective: Design and develop an environmentally safe drop-in alternative alloy as a substitution for highly loaded bushing applications. p. 3
Problem / Need Statement Health risks associated with exposure to CuBe OSHA recommends less than 0.2 µg/m³ - 8hr (TWA) Primary concern is beryllium dust fume inhalation Copper Beryllium Disease (CBD), lung cancer, potentially fatal Beryllium is categorized as a hazardous material Increasingly stringent control regulations Escalating operations costs CuBe alloy extensively employed for highly loaded airframe wear applications (approaching UTS = 180 ksi) Alternative alloys required to fulfill performance requirement and support new platform development and fleet supply/manufacturing and sustainment p. 4
Previous Alternatives to CuBe Properties of available alternative alloy materials do not meet the full range of design requirements p. 5
Systems Design: L1 2 -strengthened CoCr Processing Structure Properties Performance Tempering Machining Solution treatment Hot working >4 dia. Homogenization VIM/VAR melting Matrix - FCC (avoid HCP transformation) - Low SFE - Solid solution strengthening Nanostructure - Low-misfit L1 2 - Size & fraction - Avoid embrittling phases Grain Structure - Grain size - GB chemistry - pinning particles - Avoid cellular reaction Solidification structure - Inclusions - Eutectic Non-toxic Strength -120 to 180 ksi compressive YS - CW not required for strength Wear - Low CoF - Galling/fretting resistance Toughness -Highly ductile after solution treat - High toughness fully hardened Corrosion Resistant Environmentally Friendly Bearing Strength Wear Resistance Damage Tolerant Formable Corrosion Resistant p. 6
Design Concept: CoCr alloy with precipitation strengthening High Cr content Wear/Corrosion Minimize the hardness and ease of machining in annealed state Minimize interstitial elements (C, N) Most machining before final solution heat treatment Design for a precipitation-strengthening dispersion Solution-treatable following (rough) machining in annealed state Efficient precipitation during tempering > ~700-900 C Coherent phase is ideal: (L1 2 or γ ) Co 3 Ti Similar microstructures demonstrated for CoAlW (Crfree) alloy, but we need Cr (SFE) Ensure good lattice parameter matching between the FCC matrix and ordered FCC (L1 2 ) particles Design for good solidification and hot-working Design for an efficient grain pinning dispersion TiC/VC can be effective at low phase fraction J. Sato et al., vol. 312, Science, 2006 p. 7
Co System Thermodynamics with L1 2 γ Develop thermodynamic database Search composition space for achieve targeted microstructure Co-Cr-Ti-W-Fe-Ni-V-C multicomponent thermodynamic database assessment complete Design for FCC L1 2 lattice parameter matching for stable, coherent dispersion Avoid cellular growth reactions at grain boundary (Cr, Fe & V to reduce misfit) Stabilize FCC (vs. HCP) at tempering temperature (Fe, Ni) Al Ti Iso-section at 1173K γ γ Co W Co Cr p. 8
Lab-scale Proof of Concept Solidification and Homogenization Large grains with significant twinning No evidence of large particles on the grain boundaries, nor dispersed in the matrix As-cast ~9% eutectic Homogenized at 1060 C: mostly homogenous p. 9
Lab-scale Proof of Concept Temper Study 850 C /8 hr 850 C /24 hr Annealing twins (evidence of FCC with low SFE) No cellular growth (discontinuous precipitation) or unusual grain boundary particles p. 10
Lab-scale Proof of Concept L1 2 Precipitation Nanostructure Annealing twin in FCC grain Nano-scale (~100 nm) particles with cubic orientation to matrix - evidence of L1 2 phase p. 11
Validation of Design with LEAP Validation of alloy nanostructure using atom probe tomography after tempering at ~780 C: FCC (Co-rich) matrix and γ (L1 2 crystal structure, Co 3 Ti-type) strengthening nano-precipitates Matrix Co Precipitate hanced Cr Side view Matrix is enhanced in Fe, Cr Precipitate is enhanced in Co, Ti; Cr slightly enhanced in Ni, V Ni Fe Precipitate is enhanced in Co, Ti; slightly enhanced in Ni, V Ti Top view p. 12
Design Iteration: Optimize Strength and Processability 1 st Gen (NGCO-1A) 3 rd Gen (NGCO-3A) γ =16% L γ γ =22% L γ Solution window CALPHAD step diagrams from QuesTek proprietary database p. 13
Scale-up Production and Process Optimization Alloy production (500 lb. VIM/VAR scale) Manufacturing Process Flow & Rotary Hammer Forging System 4 and 2 Billets p. 14
Scale-up Production and Process Optimization Alloy production (500 lb. VIM/VAR scale) after forging Tempered condition for 1 st Generation characterization (aged at 780C/24 hours Hardness of 34.8 HRC) Heat treatment optimization is performed by isothermal holding at different aging temperatures for various times (note long times). 410 HV T = 780 C The peak hardness condition is identified as 780 C for 72 hours p. 15
Strength Performance Comparisons NGCo-3A Tensile Comparison Shows Best Down-Select Candidate p. 16
QuesTek Cobalt Alloy Property Comparison Designed for low-friction bushing applications as an alternative to high-strength CuBe alloys The new design has demonstrated better wear resistance in pin-on-disk and reciprocating wear tests, compared to baseline AMS4533 CuBe alloy. Additional interest from turbine engine OEMs QuesTek patent pending Room Temperature Tensile Property QuesTek Cobalt* Haynes 188 (AMS 6508 Sheet) Haynes 25 (Hot-rolled + Annealed Bar) Haynes 556 (Hot-rolled + Annealed plate) Ultimet (Solution Treated Bar) Stellite 6 (Investment Cast) Tensile Strength 200 ksi 137 ksi 147 ksi 116 ksi 147 ksi 115 ksi 0.2% Yield Strength 127 ksi 67 ksi 73 ksi 55 ksi 76 ksi 96 ksi Elongation 33% 53% 60% 51% 38% 3% Reduction in Area 28% - - - - 3% Hardness, RC 38 30 41 * Based on initial evaluations of 2 round hot forged bar, solution treated and aged at 780 C, produced at 500 lb. VIM + VAR scale p. 17
Galling Performance Comparisons NGCo-3A Galling Shows Equivalent Performance to Cu-Be NGCo-3A has Lower Coefficient of Friction (Better Wear Performance) p. 18
Fatigue Performance Comparison NGCo-3A Fatigue Life Comparison Shows Superior Performance p. 19
Environmental Bushing Testing Performance NGCo - 3A Lower Rotational Load Lower Temperature Response Equivalent Static Wear Displacement CuBe Higher Rotational Load Higher Temperature Equivalent Static Wear Displacement NGCo-3A was Superior in Galling Initiation Test Evaluation p. 20
CHiMaD: Explore Concepts to Reduce Temper Time to Peak Hardness p. 21
Co Database Updates Based on LEAP and Literature Data 780 C/2h 780 C/72h 780 C/260h Refinement of thermodynamic database using new LEAP analysis of γ particle evolution at 780 C Refinement of Ni kinetic database using literature Co diffusivity data D of Cr in FCC Co (m^2/s) 1E-13 1E-14 1E-15 Experimental Fitting Ni-mob2 Old database NIST-Ni p. 22
NIST CHiMaD CALPHAD Co-database Development Co-Al-W-Ni-Ti-Ta-Nb-B-Cr-Fe-V-Mn Initial focus 2 nd focus 3 rd level focus NIST γ/γ Co-base Superalloy Workshop: June 23-24, 2015 Eric Lass eric.lass@nist.gov p. 23
Estimation of particle evolution with updated databases Particle Size Distribution (PSD) evolution. 1E37 PSD (#/m 3 ) 1E36 1E35 1E34 1E33 1E32 1E31 1E30 t=0.01s t=0.1s t=1s t=10s t=100s t=1e3s t=1e4s t=1e5s t=1e6s t=1.44e6s NGCO-3A alloy simulated at 780⁰C for 400hrs 1E29 1E28 1E27 1E26 1E-10 1E-9 1E-8 1E-7 Radius (m) p. 24
Strength Model Calibrated to Peak Aged Condition Kozar, R. W., Suzuki, A., Milligan, W. W., Schirra, J. J., Savage, M. F., & Pollock, T. M. (2009). Metallurgical and Materials Transactions A, 40(7), 1588-1603. p. 25
Exploration of Two-step Tempering Process 60 50 40 (KSi) 30 Two Steps: 20 10 0 0 20 40 60 80 100 Time (hrs) 780C 800C 820C 780C+680C 800C+680C 820C+680C Higher Temp faster nucleation, growth & coarsening of precipitates Lower Temp further increase volume fraction to peak strength p. 26
Summary Thermodynamic and process modeling ICME tools have been applied to the design of L1 2 precipitate-strengthened high-strength wear-resistant Co-base alloy A full-scale prototype has been produced and extensive performance testing shows excellent properties and high potential for the alloy as a CuBe replacement CHiMaD 2014 Activities Extension of Co CALPHAD thermodynamic and kinetic databases based on LEAP and literature data Calibration of strength model to full-scale prototype data Prediction of two-step temper to reduce time to peak strength p. 27
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Conceptual Design: Co-Cr-Ti-V-Ni-Fe Full equilibrium Suspend laves, Co 4 Cr 2 Ti HCP Co 4 Cr 2 Ti laves HCP eta Calculation using QuesTek Proprietary database Key design challenges are to: 1) avoid HCP; 2) avoid eta during tempering; 3) avoid Co 4 Cr 2 Ti phase while maintaining high Cr p. 29
Alternative Copper Beryllium Alloys Development Vertical Tail Hinge Assembly Objective: Design and develop a environmentally safe drop in alternative alloy as a substitution for highly loaded bushing applications. Wing Lug Attach Main Landing Gear Approach: Research preferred alloys for initial base material selection. Develop selected alloy material attributes to meet specific performance requirements. Execute alloy down selection utilizing known characterization test methods to pinpoint best performance results. Perform environmental comparisons tests to validate that alternative alloy meets or exceeds drop in usage specifications p. 30
Design Using Finite Element Modeling (ABAQUS) Modeling Views Illustrate Bushing and Pin Geometries That Mimic Full Scale Environmental Testing p. 31
Most promising concepts and the risks associated with each alloy p. 32
Environmental Bushing Testing Perform Full-scale Environmental Bushing Tests Threshold - High Load Low Speed Oscillation Oscillate +25 to -25 ( Initiate at 0 fully reversed) Initial load 2,000 lbs / Final load 10,000 lbs Increase 500 lbs every 100 cycles Endurance - Moderate Load Continuous Rotation Applied load 500 lbs Rotate @ 30 Rpm p. 33