Faculty of Engineering


High performance nanoparticle-reinforced composite coatings

This is a Marsden funded project that aims to understand how nano-dispersion is realised in our new solution mixing method for composite coatings and how the mechanism can be used to create stronger materials and coatings.

Image to the right: The microstructure of Ni-TiO2 composite coatings formed by a) traditional solid particle mixing and b) new method of solution mixing. The new technique produced much better particle dispersion.

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The 21st Century has been called the “Nano Century” with intensive research in nanoscience and nanotechnology. One exciting research area focuses on dispersing nano-sized particles in a coating matrix to form composite coatings. The microstructure, mechanical properties, corrosion resistance, and colour of the coatings can be significantly improved/changed by the nanoparticle dispersion.

It is well known that dispersion of nanoparticles is the main mechanism for strengthening a material: the smaller the particles size and shorter the particle distance, the higher the strengthening effect. Solid nano-powders are traditionally used to synthesize particle reinforced composite coatings. This traditional process is using electrochemical deposition with nano-sized solid particles mixing into an electrolyte solution. Both nano-sized particles and metal ions co-deposit onto the surface of working parts, forming metal-matrix nano-composite coatings.

However, it is difficult to achieve a good dispersion for particles especially when they are in the nano-meter level due to their very large surface area and surface energy. The nano-particles tend to join (agglomerate) together. We recently discovered a new method that can avoid particle agglomeration by solution mixing instead of adding solid powders, leading to true dispersed nano-particle distribution.

Current major developments


We recently discovered a new method that can avoid particle agglomeration and form highly dispersed oxide reinforced composite coatings. We added a small amount of solution containing TiO2 components into the traditional Ni plating solution instead of solid powder, leading to “true nano” particle distribution with much greater property improvement. The hardness and wear resistance of the coating can be improved by 40-100% compared to the solid particle mixing method. We have successfully applied this new technique in different experimental systems, including:

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Surface morphologies of Ni-TiO2 composite coatings by a) traditional solid-particle mixing method showing agglomeration, and b) solution addition method with a smooth and compact surface. The denser and smoother surface results in improved corrosion resistance.
  • Nickel-phosphorous-titanium oxide (Ni-P-TiO2) electroless coatings on magnesium alloys. The micro hardness reached 1045 Hv, comparable to the traditional hard chrome coatings but does not use harmful Cr+6 processes.
  • Nickel-phosphorous-titanium oxide (Ni-P-TiO2) and Nickel-phosphorous-zirconium oxide (Ni-P-ZrO2) electroplating on carbon steels, aluminium alloys and copper alloys, with superior hardness and wear resistance.
  • Copper based composite coatings on copper and aluminium with much improved wear resistance and high conductivity (for electrical contacts).
  • Black nickel composite coatings with superior corrosion resistance for solar thermal energy absorption.
  • Gold coatings with improved wear resistance for decoration or electrical contacts.

Key focus areas/issues


In this project, we aim to:

  1. Understand the formation mechanism of the dispersed nano-particles.
  2. Investigate the effect of sol addition on the microstructure.
  3. Understand the effect of highly dispersed nano-particles on the properties of coatings.
  4. Optimise this method to create a wide range of wear, corrosion and high temperature resistant coatings for various industrial applications. 
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Key achievements


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Surface of Ni composite coating on steel: (a) traditional solid-particle mixing, (b) sol-enhanced black coating. (c) Low reflectance in the range of visible light for the Ni black coating (b).

Highly-dispersed nano-particle reinforced composite coatings have been prepared with the new solution mixing method. The new coatings show significantly improved hardness and wear resistance by 40-100%. Corrosion resistance is also enhanced, evidenced by almost no corrosion during a 120 h salt spray test. Our new method can produce coatings with some special features. For instance a uniform ultra-black coating that can absorb ~99.5% of light/radiation energy has been made with the sol enhanced electroless method. We found that the coatings have very fine and dense crevice structures on the surface which capture the visible light efficiently.

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Gold coatings on brass: (a) traditional Au coating, (b) sol-enhanced Au coating, and (c) ) wear losses of three coatings after identical wear tests: (a) pure gold coating, (b) gold coating with solid mixed oxide particles, and (c) gold coating with sol-enhanced nano-composite coating, showing much reduced wear loss.

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Wear tracks after identical wear tests: (Cr) on traditional hard chrome coating, (Ni) on our Ni-P-TiO2 coating.

Key people


Wei Gao
Chemical and Materials Engineering

Michelle Dickinson
Chemical and Materials Engineering

Weiwei Chen
Chemical and Materials Engineering

Contact


Wei Gao
Email: w.gao@auckland.ac.nz
Phone: +64 9 373 7599 extn 88175

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Related publications


Chen, W.W. and Gao, W, 2009. Plating or Coating Method for Producing Metal-Ceramic Coating on a Substrate. Patent NZ578038, Auckland UniServices, New Zealand.

Chen, W.W. and Gao, W., and He, Y.D., 2009. A novel electroless plating of Ni-P-TiO2 nano-composite coatings, Surface and Coatings Technology, vol. 204(15), pp. 2493-2498.

Chen, W.W. and Gao, W., 2009. Sol-gel enhanced Ni-P composite coatings, in High Performance Coatings for Automotive and Aerospace Industries, Nova Science Publishers Inc., New York.

Chen, W.W., He, Y.D. and Gao, W., 2010. Electrodeposition of sol-enhanced nanostructured Ni-TiO2 composite coatings, Surface and Coatings Technology, vol. 204 (15), pp. 2487-2492.

Chen, W.W., Gao, W. and He, Y.D., 2010. Sol-enhanced triple-layered Ni-P-TiO2 composite coatings, Journal of Sol-Gel Science and Technology, vol. 55 (2), pp.187-190.

Chen, W.W., He, Y.D. and Gao, W., 2010. Synthesis of nanostructured Ni-TiO2 composite coatings by sol-enhanced electroplating, Journal of the Electrochemical Society, vol. 157(8), pp. E122-E128.

Chen, W.W. and Gao, W., 2010. Sol-enhanced electroplating of nanostructured Ni-TiO2 composite coatings – The effects of sol concentration on the mechanical and corrosion properties, Electrochimica Acta, vol. 55(22), pp. 6865-6871.

He, Y.D., Fu, H.F., Li, X. G. and Gao, W., 2008. Microstructure and properties of mechanical attrition enhanced electroless Ni-P plating on magnesium alloy, Scripta Materialia, vol. 58(6), pp. 504-508.

Yao, M., He, Y., Wang, D. and Gao, W., 2007. Nano-Micro-Laminated (ZrO2-Y2O3)/(Al2O3-Y2O3) Composite Coatings and Their Oxidation Resistance, Oxidation of Metals, vol. 68(1-2), pp 1-9.

Liu, Z.M. and Gao, W., 2006. Electroless nickel plating on AZ91 Mg alloy substrate, Surface and Coatings Technology, vol. 200(16-17), pp. 5087-5093.

Li, Z.W., Gao, W., Zhang, D.L. and Cai, Z.H., 2004. High temperature oxidation behaviour of a TiAl–Al2O3 intermetallic matrix composite, Corrosion Science, vol. 46(8), pp. 1997-2007.

Li, Z.W. and Gao, W., 2003. Improved oxidation resistance of Ti with a thermal sprayed Ti3Al(O)–Al2O3 composite coating, Scripta Materialia, vol. 48(12), pp. 1649-1653.

Gao, W., Liu, Z. and Li, Z.W., 2001. Nano- and Micro-crystal Coatings and Their High-Temperature Applications, Advanced Materials, vol. 13(13), pp. 1001-1004.

Liu, Z., Gao, W., Dahm, K., and Wang, F., Oxidation Behaviour of Sputter-Deposited Ni-Cr-Al Micro-Crystalline Coatings, Acta Metallurgica and Materialia, vol. 46(1998) 1691-1700.

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This project has been made possible with the support of the Marsden Fund.