WC-based cermet coatings produced by cold gas dynamic and pulsed gas dynamic spraying processes M. Yandouzi a, ⁎ , E. Sansoucy a , L. Ajdelsztajn b , B. Jodoin a a University of Ottawa, Ottawa, Ontario, Canada b University of California, Davis, California, USA Received 9 February 2007; accepted in revised form 30 May 2007 Available online 6 June 2007 Abstract Due to their mechanical properties, WC-based cermet coatings are extensively used in wear-resistant applications. These coatings are usually produced using thermal spray processes. However, due to the nature and the environment of these spraying processes, the feedstock powder structure and properties suffer from decomposition, which subsequently degrade the performance of the coatings produced. The cold gas dynamic spraying process appears to be a promising alternative technique to preserve the properties of the feedstock powder during the coating preparation. Although the latter technique can minimize or eliminate the degradation of the sprayed material, the deposition of cermet using this technique is a difficult task. In this study, two types of cermet powders, the nanocrystalline (WC–15Co) and the conventional (WC–10Co4Cr) powders were deposited using the cold gas dynamic spraying and the pulsed gas dynamic spraying processes. The feedstock powders and coatings microstructures were investigated by OM, SEM and XRD, as well as their hardness. The results revealed the possibility of depositing cermet coatings onto aluminum substrates using both processes without any degradation of the carbide phase of the feedstock powder. The cold gas dynamic spraying process experienced difficulty in depositing and building up dense coatings without major defects. The pulsed gas dynamic process produced thick cermet (conventional and nanocrystalline) coatings with low porosity as long as the feedstock powder was preheated above 573 K. © 2007 Elsevier B.V. All rights reserved. Keywords: Cold gas dynamic spraying; Pulsed gas dynamic spraying; Nanocrystalline; WC–15Co; WC–10Co–4Cr; Coatings 1. Introduction WC–Co cemented carbide (or cermet), in the form of sintered components or coatings has been successfully used to provide wear resistance in a wide range of applications, par- ticularly in the heavy machinery sector [1]. The excellent wear resistance exhibited by these cemented carbides is attributed to their unique combination of high hardness and moderate levels of fracture toughness. A large variety of metallic matrix mate- rials (Co, Cr, Ni, etc.) are available to incorporate the WC grains. The best performance in terms of wear resistance is reached with cobalt [2]. However, the corrosion resistance of this composite is insufficient for many applications. In such cases, preference is given to coatings produced from commer- cially available WC–CoCr spray powders, in which the chro- mium addition provides an improvement in the corrosion resistance of the metallic binder phase over that of unalloyed WC–Co [3,4]. Cemented carbides wear properties have been extensively investigated over the years and it has been found that the abrasive wear resistance of sintered cermet is generally improved by a reduction of the binder volume fraction and a decrease of the carbide particle size [5]. Moreover, it has been reported that sintered WC-based nanocrystalline materials show greater wear resistance compared to the conventional (non- nanocrystalline) ones [6]. It is envisioned by the hard metals industry that nanocrystalline cemented carbide coatings could offer new opportunities for achieving a combination of superior hardness and toughness [7]. Available online at www.sciencedirect.com Surface & Coatings Technology 202 (2007) 382 – 390 www.elsevier.com/locate/surfcoat ⁎ Corresponding author. Mechanical Engineering Department, Faculty of Engineering, University of Ottawa, 770 King Edward Avenue, Ottawa, Ontario, Canada K1N-6N5. E-mail address: yandouzi@uottawa.ca (M. Yandouzi). 0257-8972/$ - see front matter © 2007 Elsevier B.V. All rights reserved. doi:10.1016/j.surfcoat.2007.05.095