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P.L. Bonora , M. Lekka

P.L. Bonora , M. Lekka

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P.L. Bonora , M. Lekka

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  1. P.L. Bonora, M. Lekka Development and electrochemical characterization of metal matrix nano/micro composite electrodeposits University of Trento, Department of Materials Engineering and Industrial Technologies, Lab. of Industrial Corrosion Control

  2. INTRODUCTION • Metal composite coatings: • Metal or alloy • + particles of: • Oxides (SiO2, Al2O3, Cr2O3) • Carbides (SiC, WC, TiC, Cr3C2) • Nitrides (TiN, CrN) • Graphite • Diamond • Polymers (PS, PTEE, PCMF)

  3. INTRODUCTION • The incorporation of a homogeneously dispersed second phase material in a metal or alloy matrix, leads to surface coatings with improved or sometimes completely new properties Dispersion hardened and abrasion resistant composite coatings Corrosion resistance composite coatings Incorporation of dispersed hard particles (SiO2, Al2O3, Cr2O3, SiC, WC, TiC, Cr3C2, diamonds …) Till a 2-4% wt. of particles increase of wear resistance Ultrafine particles might increase the corrosion resistance by modifying the deposit’s microstructure Self-lubrifying composites The introduction of a solid lubricant (graphite, molibdenumbisulfide, PTFE) decreases the wear coefficient even under high load.

  4. INTRODUCTION • Uses: • Ship building • Railways • Food processing industry • Car bodies and engines • Power plants • Production methods: • Powder metallurgy • Coprecipitation • Mechanical Mixing • Metal Spray Deposition • Chemical Vapor Deposition • Physical Vapor Deposition • Laser Surface Treatment • Electrodeposition

  5. A LITTLE BIT OF HISTORY... • One of the oldest references where a metal matrix composite system appeared was in 1928 and regards the production of Cu/graphite coatings. • The first systematic attempts for the use of the codeposition method for the production of composite coatings are made in the late 60’s when the SiC particles are used to improve the tribological behaviour of Ni coatings. At the same period other types of composite coatings were produced using metal matrixes of Ni, Cu or Ni-Cu alloy and carbides, oxides, diamond powder and PTFE as reinforcement. • Later on, the codeposition technique attracted the interest of other scientists but also of the industry. The first electroplating baths containing particles appeared in industrial scale for the production of Ni/SiC and Co/Cr2O3 coatings used for car engines, aircrafts construction and printed circuits. Specifically the Ni/SiC deposits have been used as internal coating of the aluminium cylinders of car engines,.

  6. A LITTLE BIT OF HISTORY... • In the last 10 years the interest on the metal matrix composite coatings has been revived due to two main factors: • the need of new hard and wear resistant coatings to substitute the hard chromium coatings and • the development of new nanotechnology methods for the production of nano-particles of carbide or oxides, whose incorporation into metal matrixes could attribute completely different properties to the composite coatings. J.P. Celis, J.R. Ross, Reviews on coatings and Corrosion, V(1-4) (1982), 1-41 J. Ross, J.P. Celis, J. Fransaer, C. Buelens, JOM, (1990) L. Shaw, JOM, (2000)

  7. PARTICLES CODEPOSITION IN METAL MATRIXES • Electrodeposition from a galvanic bath containing the particles in suspension • The particles are “pushed” towards the cathode and embedded into the metal matrix • There are many models trying to clarify the process

  8. OUTLINE • The Ni/SiC system: • Influenceof the bathtype (Watts and sulphamate) • Influenceof the particlessize (micro- or nano-) • Influenceof the currenttype (direct or pulse) • Microstructure • Hardness • Abrasion resistance • Corrosion resistance • Application examples, scaling-up, industrialization

  9. SPECIMENS PRODUCTION • SiC powders • Substrate: Low carbon steel • Preparation Polishing Degreasing Acid etching Micro SiC Nano SiC • Nickel bath • Applied current: • 240 g/l NiSO4 • 45g/l NiCl2 • 30g/l H3BO4 • 2.5g/l CH3(CH)11OSO3Na • Direct • Pulse • Square shape • Duty cycle • Frequencies: 0.01, 0.1, 1, 10, 100 Hz • Temperature: 50oC • pH: 4.5 • Stirring: Mechanical 200rpm • Current density: 2A/dm2

  10. Ni/SiC - MICROSTRUCTURE Ni-DC Ni-0.01Hz Ni-1Hz Ni-0.1Hz Ni-10Hz Ni-100Hz Ni+nSiC -0.1Hz Ni+nSiC -0.01Hz Ni+nSiC -1Hz Ni+nSiC -100Hz Ni+nSiC -10Hz Ni+μSiC-DC Ni+nSiC-DC

  11. Ni/SiC - MICROSTRUCTURE 10 Hz DC DC 10 Hz Ni Ni nano-composite Ni+μSiC-100Hz


  13. Ni/SiC ABRASION RESISTANCE Ni+μSiCabrasion trace Ni+nSiCabrasion trace

  14. Ni/SiC ELECTROCHEMICAL CHARACTERIZATION • Acidic environment: 0,5 M Na2SO4 +H2SO4 pH 2,5 • Alkaline environment: 0,5 M Na2SO4 +NaOH pH 11 • 3 electrodes system • Reference: Ag/AgCl • Sweep rate 0,1 mV/s



  17. Ni/SiC RESISTENCE TO PITTING CORROSION • Exposure to the salt spray according to ASTM B117 • 7 specimens of each type • Visual observations and E.I.S. measurements every 5 days • E.I.S. measurements • 3 electrode system • Electrolyte: 3.5% w/w Na2SO4 • Frequency range: 10mHz-100kHz • Applied AC potential: ± 10mV

  18. Ni/SiC RESISTANCE TO PITTING CORROSION Visual observations


  20. Ni/SiC RESISTANCE TO PITTING CORROSION Equivalent circuits

  21. Ni/SiC RESISTANCE TO PITTING CORROSION Pure nickel deposits

  22. V.O. E.I.S. Ni/SiC RESISTANCE TO PITTING CORROSION Micro-composite deposits

  23. V.O. E.I.S. Ni/SiC RESISTANCE TO PITTING CORROSION Nano-composite deposits

  24. Ni/SiC RESISTANCE TO PITTING CORROSION Visual observations E.I.S. Pure or micro-composite nano-composite

  25. Cu/SiC COATINGS MICROSTRUCTURE Cu +μSiC – 20μm Cu – 20μm Cu +nSiC – 20μm Pure copper Cu +μSiC – 70μm Cu – 70μm Cu +nSiC – 70μm Nanocomposite

  26. DC DC DC DC Brass Cu/SiC COATINGS ABRASION RESISTANCE Copper Copper + nano SiC Copper+ micro SiC DC Weight loss (g) 1 HZ DC Number of cycles DC

  27. SCALING-UP / INDUSTRIALIZATION Ni + nSiC deposits Cu + μSiC deposits Propellermodels Pasta extruders Propeller profiles Train axels

  28. SCALING-UP / INDUSTRIALIZATION Industrial samples – exposure to salt spray Nickel + nano SiC Nickel 7 d 30 d 45 d 30 d 7 d 45 d 90 d

  29. SCALING-UP / INDUSTRIALIZATION Train axels testing under real conditions When mounted After 250000km

  30. Ni/SiC CONCLUSIONS • The application of the pulse current for the production of pure Nickel deposits causes a grain refinement more evident at the frequencies of 0.1-100 Hz. A progressive increase of micro hardness (17% max) has no effect on corrosion resistance. • The micro-composite deposits present the highest microhardness and abrasion resistance strictly related to the SiC content, but the lowest resistance towards localized corrosion. The use of the pulse current increases corrosion resistance. • The codeposition of the nanoparticles causes a further grain refinement, a slight microhardness increase, a noticeable increase of wear resistance and the highest increase to localized corrosion.

  31. CONCLUSIONS • The addition of SiC micro-particles drastically increases the abrasion resistance of both nickel and copper matrix deposits but penalizes the protective properties • The addition of SiC nano-particles refines the deposits microstructure thus producing more compact coatings with improved protective properties and a good abrasion resistance • The use of pulse current influences the amount of codeposited SiC, refines the microstructure and improves the protective properties • Each specific composite system has different required properties and so specific process parameters are needed to obtain the best results. A specific study for each system is therefore necessary. • The knowledge of the process parameters and their critical aspects are required for a successful scaling-up and industrialization with slight modifications of the existing industrial plants.

  32. P.L. Bonora, M. Lekka Development and electrochemical characterization of metal matrix nano/micro composite electrodeposits University of Trento, Department of Materials Engineering and Industrial Technologies, Lab. of Industrial Corrosion Control