Contents lists available at ScienceDirect Surface & Coatings Technology journal homepage: www.elsevier.com/locate/surfcoat Heat treatment of ultrasonic electrodeposited Ni-W/ZrO 2 nanocomposites E. Beltowska-Lehman a, ⁎ , A. Bigos a , M.J. Szczerba a , M. Janusz-Skuza a , L. Maj a , A. Debski a , G. Wiazania b , M. Kot b a Institute of Metallurgy and Materials Science of the Polish Academy of Sciences, 25 Reymonta St., 30-059 Krakow, Poland b Faculty of Mechanical Engineering and Robotics, AGH University of Science and Technology, 30 Mickiewicza Av., 30-059 Krakow, Poland ARTICLE INFO Keywords: Ni-W/ZrO 2 nanocomposites Electrochemical deposition Heat treatment Microstructure transformation Wear and corrosion resistance ABSTRACT Metal matrix composite (MMC) coatings of zirconium oxide (ZrO 2 ) in nanocrystalline Ni-W alloy were obtained by ultrasound assisted direct current electrodeposition from aqueous plating electrolyte. In the present study, effects of the heat treatment (in the range of 400 °C–800 °C, in argon atmosphere) on the microstructure and physicochemical properties of hard Ni-W/ZrO 2 coatings deposited on steel substrates were investigated. It was found that thermal treatment considerably affected the microstructure of Ni-W/ZrO 2 coatings, including phase compositions, surface morphology and grain size. Microstructure features of annealed composite coatings were correlated to tribological and mechanical properties. A significant improvement in hardness (12 GPa) and wear index (0.56 mm 3 /Nm) of Ni-W/ZrO 2 nanocomposites was achieved by thermal treatment at 500 °C compared to as-deposited coatings (8 GPa and 1.5 mm 3 /Nm, respectively). At higher temperature (about 600 °C), a tendency towards phase separation was observed and iron diffusion from the substrate to the composite coating layer became evident. 1. Introduction In recent years, the requirements for advanced or alternative ma- terials for industrial uses in aggressive environments at elevated tem- perature have become increasingly important. For economic efficiency, protective and functional coatings are being developed in order to protect working surfaces of cheaper or easier machined base material from mechanical and corrosion damage [1]. In particular, Ni-W alloy characterised by excellent mechanical, wear and corrosion properties, appears to be among the most promising materials that provide the required properties to the surfaces to be coated, intended for various engineering applications [2]. It is also well known that the addition of tungsten has been used to stabilise the mi- crostructure of pure nickel in devices operated at elevated temperatures [3]. Large atoms of tungsten provide solid solution strengthening to high-temperature alloys based on ferrous metals such as nickel. More- over, the substitution of nickel by tungsten results in a significant de- crease of the thermal expansion coefficient [4]. Composites with various types of inert ceramic particles such as oxides, carbides or nitrides allow further tailoring of Ni-W alloy prop- erties, and additional grain microstructure stability [5]. Compared to the alloy coatings, composites usually exhibit enhanced properties such as remarkable hardness and tensile strength, superior wear and corrosion resistance, self-lubrication, etc. Among various ceramic reinforcing particles, zirconium(IV) dioxide ZrO 2 is distinguished by excellent physicochemical properties such as high melting point, extreme hardness, high strength, thermal and che- mical stability, wear and corrosion resistance [6]. Moreover, zirconia and nickel-based alloys are usually compatible due to similar thermal expansion coefficient and elastic modulus [7]. Electrodeposition (bottom-up synthesis method, i.e., the atomic de- position process) is one of the most important surface finishing tech- nologies. Electrochemical deposition from aqueous electrolytes, under normal pressure and ambient temperature at high plating rate, is a simple, versatile and economical technique to synthesise (uniformly and efficiently) high-purity, porosity-free alloys and compounds, with no post-processing requirements (a one-step process without the need for additional surface treatments) [8]. Electroplating is a particularly advantageous technology for the deposition of ferrous metal alloys containing refractory components such as tungsten, which are difficult to obtain by conventional alloying processes due to the enormous dif- ferences in melting points and limited mutual solubility [9]. Moreover, electrodeposition as surface modification technique, is also widely used for the production of metal matrix composites (MMCs), including na- nocomposites. Currently, nanocomposite coatings are used mainly to protect automotive parts subjected to corrosive environments, and are https://doi.org/10.1016/j.surfcoat.2020.125779 Received 28 February 2020; Received in revised form 10 April 2020; Accepted 13 April 2020 ⁎ Corresponding author at: Institute of Metallurgy and Materials Science of the Polish Academy of Sciences, 25 Reymonta St., 30-059 Krakow, Poland E-mail address: e.beltowska@imim.pl (E. Beltowska-Lehman). Surface & Coatings Technology 393 (2020) 125779 Available online 26 April 2020 0257-8972/ © 2020 Elsevier B.V. All rights reserved. T