COLD SPRAY COATINGS FOR WEAR APPLICATIONS
Friday, June 18, 2010 at 02:16PM Wear resistance of materials and coatings rely on two main characteristics, namely hardness and toughness. Finding a monolithic material that has both of these characteristics is challenging; hence, cermet materials such as WC-Co with both hard ceramics and ductile metals have proven to be quite popular for many wear applications. During the early years following the introduction of cold spray process to North America in the 1990’s, cold spray coatings were limited to ductile materials that could undergo plastic deformation during impact with a solid surface. Hence hard and brittle materials such as monolithic ceramics were not cold sprayable. Even adding some metallic phase with hard phase powder yielded limited success mostly in the form of very thin monolayer deposits.
In the past few years, many of the cermet materials have been successfully deposited beyond monolayer thicknesses using cold spray. The key is to preheat (i.e., above 300 °C) the powder to further enhance the ductile nature of the metallic matrix phases upon impact. Yandouzi et al. [i] have shown how increasing the particle velocity and/or temperature at impact can significantly improve on coating density and hardness. It is important to note; however, that the increase in particle temperature can be kept well below the level where temperature-sensitive hard phase materials such as WC undergo thermal degradation and where nanostructured metals undergo grain growth. Hence controlling the range of particle temperature at impact that will retain all of the positive attributes of the cold spray process (i.e., no grain growth, no oxidation, no change in composition) while allowing for the deposition and build up of quality hard cermet coatings is key to success.
The following are examples of cermet and metal coatings, as well as their attributes, which have been deposited via cold spray:
- § Bronzes, due to their high strength, good elasticity, good wear, and corrosion resistance, have been cold sprayed for bearing applications; [ii]
- § Cold sprayed Cr3C2-based coatings possessed increased hardness, improved wear resistance, and lower friction; [iii]
- § Bronze-diamond and NiCrAl-diamond composite coatings were successfully deposited using cold spray without degrading the diamond particles; [iv], [v]
- § Al2O3 was added to Al and cold sprayed to protect Mg parts with increased hardness, wear resistance and superior corrosion resistance; [vi]
- § Cold spray of milled Cu-MoS2 resulted in a dense, thick coating that could be tailored to possess higher hardness, superior wear resistance, and reduced coefficient of friction; [vii] and
- § The deposition of WC-Co(Cr) powder, in conventional and nanostructure form, using cold spray was successfully carried out by preheating the powder; there were no signs of thermal degradation in all of the coatings. [viii], i
Although HVOF is still considered to be the favored thermal spray process for depositing wear resistant metal and cermet coatings, recent results of cold sprayed coatings look very promising.
REFERENCES
[i] M. Yandouzi, E. Sansoucy, L. Ajdelsztajn, B. Jodoin, WC-based cermet coatings produced by cold gas dynamic and pulsed gas dynamic spraying processes, Surface & Coatings Technology 202 (2007) pp. 382-390.
[ii] X. Guo, G. Zhang, W.Y. Li, L. Dembinski, Y. Gao, H. Liao, C. Coddet, Microstructure, microhardness and dry friction behavior of cold-sprayed tin bronze coatings, Applied Surface Science 254 (2007) pp. 1482-1488.
[iii] D.E. Wolfe, T.J. Eden, J.K. Potter, A.P. Jaroh, Investigation of Cr3C2-Based Wear-Resistant Coatings Applied by the Cold Spray Process, Journal of Thermal Spray Technology, Volume 15(3) September 2006, pp. 400-412.
[iv] H. Na, G. Bae, S. Yoon, C. Lee, Improved Deposition Characteristics of Diamond Enhanced by Plastically Deformed Nickel Layer in Kinetic Sprayed Bronze/Diamond Composite Coating, Thermal Spray 2009: Proceedings of the International Thermal Spray Conference, pp. 255-260.
[v] X.-K. Suo, C.-J. Li, G.-J. Yang, C.-X. Li, Formation of Diamond/NiCrAl Cermet Coating through Cold Spray, Thermal Spray 2009: Proceedings of the International Thermal Spray Conference, pp. 249-254.
[vi] K. Spencer, D.M. Fabijanic, M.-X. Zhang, The use of Al-Al2O3 cold spray coatings to improve the surface properties of magnesium alloys, Surface & Coatings Technology 204 (2009) pp. 336-344.
[vii] M. Yamada, J. Wakabayashi, M. Fukumoto, Fabrication of Cu-MoS2 Composite Coating by Cold Spraying and Evaluation of its Property, Thermal Spray 2009: Proceedings of the International Thermal Spray Conference, pp. 326-330.
[viii] G.-J. Yang, P.-H. Gao, C.-J. Li, C.-X. Li, Toughening of Cold-sprayed Nanostructured WC-12Co Deposit through using Mulitmodal WC Particles and Annealing, Thermal Spray 2009: Proceedings of the International Thermal Spray Conference, pp. 331-336.
George E. Kim, Ph.D.
F.W. Gartner
Perpetual Technologies, Inc.
email: gkim@perpetualtech.ca
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