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Structural Cold Spray Aluminum Alloys & Cold Spray Additive Manufacturing June 18, 2014 Presenter: Aaron Nardi UTRC Team: Michael A Klecka, Matthew D Mordasky,

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Presentation on theme: "Structural Cold Spray Aluminum Alloys & Cold Spray Additive Manufacturing June 18, 2014 Presenter: Aaron Nardi UTRC Team: Michael A Klecka, Matthew D Mordasky,"— Presentation transcript:

1 Structural Cold Spray Aluminum Alloys & Cold Spray Additive Manufacturing June 18, 2014 Presenter: Aaron Nardi UTRC Team: Michael A Klecka, Matthew D Mordasky, Xuemei Wang, Tim Landry Portions of this Research were sponsored by the Army Research Laboratories and was accomplished under Cooperative Agreement Number W911NF The views and conclusions contained in this document are those of the authors and should not be interpreted as representing the official policies, either expressed or implied, of the Army Research Laboratory or the U.S. Government. The U.S. Government is authorized to reproduce and distribute reprints for government purposes notwithstanding any copyright notation herein.

2 PRESENTATION OVERVIEW Similarities between cold spray to other metallic bonding processes Single particle 3D impact modeling results and interpretation Mechanisms driving mechanical properties of cold spray materials Comparison between high temperature nitrogen and lower temperature helium deposits Recent development in the mechanical properties of aluminum Additive Manufacturing with cold spray 2

3 SOLID STATE METALLIC BONDING Adhesion in tribo-contact is when two metallic surfaces come into contact and create metallic bonds at the asperity level 3 Adhesive wear W ad =C m (  1 +  2 ) W ad = Work of Adhesion  1 = Surface energy material 1  2 = Surface energy material 2 C m = Compatibility Parameter Derived from phase diagrams of pure metals Surface energy affected by surface condition Oxides Chemisorbed layers Greases

4 SOLID STATE METALLIC BONDING Cold Pressure Welding uses normal pressure to plastically deform the interface between two surfaces Surface Area Expands Fresh metal extrudes through fractures in cover layer Fresh metal surfaces bond 4 Cold pressure welding Extracted from Metal Construction, 1986, N. Bay, “Cold Welding Part 1Characteristics bonding mechanisms bond strength” Data from Journal of Engineering for Industry, 1979, N. Bay, “Cold Pressure Welding : The Mechanisms Governing Bonding” Breakdown of surface films and cover layer

5 SOLID STATE METALLIC BONDING Explosive cladding uses an explosive charge to accelerate a “flyer plate” or material to be bonded toward a substrate High levels of plastic flow of material at interface Surface layer breakdown and removal through jet formation Fresh metal surfaces bond 5 Explosive cladding/welding Images from ASM Handbook Volume 6, Solid State Welding Processes, Explosive Welding Similarities in jet formation

6 SOLID STATE METALLIC BONDING Materials compatibility enables increased bond strength Compatible bond layers Encapsulated powders Surface contamination requires higher surface expansion (strain) to achieve bonding High plastic strain of both surfaces improves bonding Material jetting from interface can eliminate or further breakdown surface contamination 6 Summary of comparisons

7 MECHANICAL PROPERTIES OF COLD SPRAY DEPOSITS Method used to measure bond strength is lug shear testing Spray thick buildup ~0.125 inches thick Machine back to create a lug where t > 0.5w and L~2w Use vise or fixture to shear lug from substrate 7 Bond strength for buildup applications of dissimilar materials Material CoupleBefore Process Development (ksi) After Process Development (ksi) Superalloy on Gray Cast Iron Aluminum to Aluminum Ta Alloy to 40 HRC Steel <537 SS to 35 HRC Steel< t w L Key to Performance Selection of interface materials based on compatibility Process development to ensure the correct physics occurs at the interface Result High quality metallic bonding capable of carrying significant loads

8 EFFECT OF PARTICLE IMPACT VELOCITY As impacting velocity increases Plastic deformation of both particle and substrate  Contacting surface area  Particle penetration  Temperature raise  Flow stress  Contact pressure  8 Higher impact velocity increases plastic flow of particle and substrate Temperature contours (note that T p0 = 236°c and T s0 = 25°c) V 0 = 612 m/s V 0 = 980 m/s V 0 = 800 m/s V 0 = 612 m/s V 0 = 980 m/s V 0 =800 m/s V 0 = 612 m/s V 0 = 980 m/s V 0 = 800 m/s ParticleSubstrateParticle on substrate

9 EFFECT OF PRE-HEATING TEMPERATURE As impacting temperature increases Plastic deformation of particle  Contacting surface area of particle  Particle penetration  (slight) Temperature raise  Flow stress  Contact pressure – negligible 9 Higher pre-heat temperatures increases particle plastic flow T p0 =25°cT p0 =127°c T p0 = 236°cT p0 = 327°c Temperature contours (90  impact) (note that V 0 = 612 m/s)

10 MECHANISMS AFFECTING MECHANICAL PROPERTIES OF COLD SPRAY DEPOSITS Region 1 – Linear elastic material deformation Dominated by consolidated density of cold spray deposit Region 2 – Initial particle plasticity Plastic deformation of particles begins to open defects between particles Larger defects drive higher crack tip opening displacement Region 3 – Large scale plasticity Any defects in the structure are exercised due to large scale plasticity Region 4 – strain localization and defect coalescence 10 Mechanisms driving properties of cold sprayed deposits

11 MECHANISMS AFFECTING MECHANICAL PROPERTIES OF COLD SPRAY DEPOSITS 11 Micro-structural evolution of inter-particle defects 11 Cut Lines Defect Opening due to high plastic strain Starting Microstructure Unetched Etched Crack extending from defect

12 MECHANISMS AFFECTING MECHANICAL PROPERTIES OF COLD SPRAY DEPOSITS Model predicts better mechanical interlock & bonding in helium deposits Critical velocity calculations indicating both should consolidate similarly 12 Simulation and test data for helium and nitrogen spray processes 12 Fracture surfaces Helium Sprayed CVR = 1.58 Nitrogen Sprayed CVR=1.45 Temperature contours Deformed shapes Helium sprayed (d p =40  m,T p0 = 236 °c, V 0 = 980 m/s) Nitrogen Sprayed (d p =40  m,T p0 = 427 °c, V 0 = 635 m/s) Substrate Particle Dominated by inter- particle fracture Helium Sprayed Nitrogen Sprayed Dominated by trans- particle fracture

13 MECHANICAL PROPERTIES OF COLD SPRAY DEPOSITS Initial process development often results in deposits with high strength but low ductility Achieving velocity near critical velocity Through process optimization it is possible to achieve high ductility with only a moderate effect on ultimate strength Changes in particle velocity, impact temperature, particle size distribution, particle morphology, particle metallurgy, or some combination of these Ductility is tied to defects more than work hardening as originally thought Ductility in a cold spray deposit is therefore a good predictor of the expected fatigue performance in both LCF and HCF 13 Aluminum deposits before and after process modifications

14 ADDITIVE MANUFACTURING WITH COLD SPRAY DEPOSITION Lightly loaded aerospace gears typically made from nitrided steel Fretting, Dithering wear, potential friction concerns Alternate approach – Spray form base gear and add wear coating to tooth surface Select base metal for weight, stiffness, thermal conductiltiy, etc. (eg. steel, aluminum, titanium) Select surface deposit for wear, friction, anti-galling, etc. (e.g. Tribaloy T-800 blend) 14 Manufacture of small lightly loaded gears with improved lubricity and wear Steel Mandrel Spray Formed Part Finished Gears Removed from substrate by thermal shock Wear layer added to spray formed part then finish machined


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