Versatility of the sputtering technique in the processing of WC–Fe–Ni–Cr composites C.M. Fernandes a , A.M.R. Senos a, ⁎, M.T. Vieira b a Department of Ceramics and Glass Engineering, CICECO, University of Aveiro, 3810‐193 Aveiro, Portugal b CEMUC, Mechanical Engineering Department, University of Coimbra, Rua Luís Reis Santos, Pinhal de Marrocos, 3030‐788 Coimbra, Portugal abstract article info Article history: Received 19 January 2012 Accepted in revised form 23 May 2012 Available online 31 May 2012 Keywords: Sputtering Tungsten carbide Stainless steel Mechanical properties Microstructure The versatility of the sputtering technique when innovatively applied to the coating of powders was investi- gated by using three different preparation methodologies to coat WC particles with Fe–Ni–Cr binder: single coating deposition of stainless steel and Ni on WC particles (CP1); sequential sputter deposition of a first Ni coating layer, followed by a second one of stainless steel (CP2) and, finally, a mixed process of Ni deposition on WC particles, followed by stainless steel addition by conventional powder mixing (CP3). The average chemical composition of the three powders was equivalent, having ~ 10 wt.% of Fe–Ni–Cr binder, but their particle surfaces were modified in different ways by the specific sputter-coating conditions, affecting the powder processing and the final composite characteristics, as follows. The composite obtained with only one sputtering step (CP1) attained almost full densification during conventional vacuum sintering, while CP2 and CP3 needed an additional hot isostatic pressing cycle to attain high enough densification. Mixed carbides, (M,W) 6 C and/or (M,W) 4 C, with M_Fe, Ni, Cr, were detected in the composites, whatever has been the processing used in powder preparation, but in different amounts. The best compromise between hardness and toughness was observed for the CP1 composite, although the phase composition shows the highest amount of fragile carbides, ~ 14 wt.% of carbides (M,W) 4 C and (M,W) 6 C. All the composites prepared by the different methods showed Ni homogenization within the metallic binder. Regarding these results, the most effective method for the composite powder preparation was the simplest one with only one deposition step (CP1), since higher densifications and enhanced mechanical properties were obtained, comparatively with the other composites (CP2 and CP3). Additionally, one can conclude that sputtering is, in fact, a versatile process which can be used to modify the powder surfaces' characteristics in different ways, affecting the powder processing and the final material properties. © 2012 Elsevier B.V. All rights reserved. 1. Introduction Innovation in the materials manufacturing industries passes through improved design and processing techniques, together with the develop- ment of new materials, in order to manufacture products with enlarged field of applications and more competitive prices. Tungsten carbide-based composites are well known materials used as cutting tools and in other applications, such as drill bits and compo- nents for mining, oil and gas drilling, transportation and construction, metal forming, structural and fluid-handling components, and forest- ry tools, among others [1]. The processing of these material starts with the powder preparation, conventionally done by wet milling all the components, typically carbides and metallic binder powders. More recently, new methods concerning the coating of WC particles with binder have been reported [2–4] which offer a variety of interesting characteristics, where the essential properties of the powder or the final product can be influenced by a specific coating layer. A variety of chemical and physical methods have been successfully applied to metallise the surface of WC particles, most of them with Co, the tradi- tional metallic binder [4–6]. However, very few reports about the effect of the powder coating on the processing and final properties can be found [7,8]. Exception is made for the systematic studies of our group, where the coating of WC powders with iron rich binders was performed using a specially developed sputtering equipment [9,10]. The sputter-coating process showed to be an innovative way to add uniformly the binder to tungsten carbide powders, modifying their surface properties, such as oxidation resistance, stability in aque- ous suspensions, flowability and green strength [3,11]. Moreover, binder nanocrystallinity and uniform distribution among the carbide particles were achieved in the sputtering deposition which promotes the attainment of high densified composites and excellent properties, in terms of hardness and toughness [9,12]. Despite that, sputter- coated powders have revealed a high chemical reactivity and further studies are yet needed to get a desired final phase composition and optimised properties. Stainless steel is a promising binder for WC based composites, since it has good ductility, higher corrosion and oxidation resistance and good sinterability at relatively low temperatures, comparatively Surface & Coatings Technology 206 (2012) 4915–4921 ⁎ Corresponding author. Tel.: + 351 234 370 354; fax: + 351 234 370 204. E-mail address: anamor@ua.pt (A.M.R. Senos). 0257-8972/$ – see front matter © 2012 Elsevier B.V. All rights reserved. doi:10.1016/j.surfcoat.2012.05.093 Contents lists available at SciVerse ScienceDirect Surface & Coatings Technology journal homepage: www.elsevier.com/locate/surfcoat