Wear properties of CrC–37WC–18M coatings deposited by HVOF and HVAF spraying processes I. Hulka a , V.A. Şerban a , I. Secoşan a , P. Vuoristo b, ⁎, K. Niemi b a Department of Materials and Welding Science “Politehnica” University of Timişoara, Blv. Mihai Viteazu, No 1, RO-300222, Romania b Department of Materials Science, Tampere University of Technology, Korkeakoulunkatu 6, FI-33101 Finland abstract article info Article history: Received 30 March 2012 Accepted in revised form 29 July 2012 Available online 4 August 2012 Keywords: CrC–37WC–18M HVOF HVAF Wear CrC–37WC–18M cermet coatings were deposited using new feedstock powders which seem to combine the properties of WC–CoCr and CrC–NiCr coatings. A conventional particle size CrC–37WC–18M powder was used as feedstock for the HVOF (high velocity oxygen fuel) thermal spraying process and a fine particle dis- tribution was used as feedstock for the HVAF (high velocity air fuel) thermal spraying process. In order to characterize the morphology of the feedstock powders and deposited coatings SEM and X-ray diffraction were used. The microhardness of the coatings was also studied. The wear behavior of the coatings was eval- uated by pin-on-disk and rubber wheel abrasion tests. The HVAF coating showed equal or even better wear resistance as compared to corresponding HVOF coatings. © 2012 Elsevier B.V. All rights reserved. 1. Introduction Thermal sprayed WC cermet coatings have been used to resist wear environments at ambient and elevated temperatures for a number of years due to their properties such as high abrasion, sliding and erosion resistance, advantages offered by dense coatings [1,2]. High velocity oxygen fuel (HVOF) thermal spraying is suitable in obtaining dense cer- met coatings with low oxidation due to its unique advantage of heating the feedstock to near or above its melting point, preferably between the solidus and liquidus temperatures, at a relatively low process tempera- ture by a supersonic combustion gas stream [3–5]. Due to high velocity, the time of interaction between the powder and the flame shortens and in conjunction with the process temperature limited thermal alteration occurs ensuring good cohesion and morphology with reduced porosity and low decarburization [6,7]. An alternative to the HVOF process, for manufacturing cermet hard coatings, is the high velocity air fuel (HVAF) process which utilizes compressed air, instead of oxygen, for combustion and operates at lower temperatures than the HVOF process [8]. The HVAF process reduces the manufacturing cost of coatings, re- placing pure oxygen by compressed air having as consequence coatings which do not show any of the oxidation or decarburization effects after spraying [9]. WC and Cr x C y based thermally sprayed coatings are extensively used to decrease the friction coefficient between various sliding components and to improve corrosion resistance in many indus- tries [10,11]. Due to the Cr content the coatings are suitable for high-temperature applications [12]. The CrC–37WC–18M is quite a new powder developed to combine the properties of WC–CoCr and CrC–NiCr cermet powders. It is composed of two carbide phases WC and Cr 3 C 2 embedded into an alloy composed of Ni, Co and a small amount of Fe. There are no studies in the literature focused on the prop- erties of CrC–37WC–18M deposited via HVOF and HVAF processes. The aim of the study was to characterize the phase and microstructure of the CrC–37WC–18M coatings deposited by HVAF and HVOF thermal spraying as well as to study the composition, abrasive and sliding wear behaviors of the coatings. 2. Experimental Two types of CrC–37WC–18M powders were used for this study: a WOKA 7502 powder with a nominal size distribution of -45+15 μm and a fine WOKA 7504 powder with a nominal size distribution of -30+10 μm. Both powders are manufactured by Sulzer Metco, Germany, by agglomeration and sintering. A Sympatec Helos laser dif- fractometer was used to determine the particle size distribution of the powders. Philips XL-30 scanning electron microscope equipped with an EDAX analyzer was used to investigate the morphology of the powders and coatings in this study. WOKA 7504 powder was deposited by the HVAF process using a M2 thermal spray gun with 0.52[MPa] propane, respectively and [0.59] MPa air as process gases. The standoff distance was 150 mm. WOKA 7502 powder was deposited by the HVOF process using a Diamond Jet Hybrid 2700 gun at TUT with 68 l/min pro- pane, 236 l/min oxygen and 368 l/min air as process gases. The standoff distance was 230 mm, traverse speed of the gun 11 mm/s and powder feed rate 60 g/min. This gun provides particle velocities up to 650 m/s. In both processes nitrogen was used as a carrier gas for the feedstock Surface & Coatings Technology 210 (2012) 15–20 ⁎ Corresponding author. Tel.: +358 40 849 0044; fax: +358 3 3115 2330. E-mail addresses: hulka_iosif@yahoo.com (I. Hulka), viorel.serban@rectorat.upt.ro (V.A. Şerban), ionut_secosan@yahoo.com (I. Secoşan), petri.vuoristo@tut.fi (P. Vuoristo), kari.niemi@tut.fi (K. Niemi). 0257-8972/$ – see front matter © 2012 Elsevier B.V. All rights reserved. http://dx.doi.org/10.1016/j.surfcoat.2012.07.077 Contents lists available at SciVerse ScienceDirect Surface & Coatings Technology journal homepage: www.elsevier.com/locate/surfcoat