Short Communication Effect of plasma nitriding on electrodeposited Ni–Al composite coating N. Daemi a , F. Mahboubi a, * , H. Alimadadi b a Department of Mining and Metallurgical Engineering and New Technologies Research Center, Amirkabir University of Technology, Hafez Ave., P.O. Box 15875, Tehran 4413, Iran b Department of Mechanical Engineering, Technical University of Denmark, Kemitorvet, Building 204, 2800 Kgs. Lyngby, Denmark article info Article history: Received 24 April 2010 Accepted 6 July 2010 Available online 31 July 2010 abstract In this study plasma nitriding is applied on nickel–aluminum composite coating, deposited on steel sub- strate. Ni–Al composite layers were fabricated by electro-deposition process in Watt’s bath containing Al particles. Electrodeposited specimens were subjected to plasma atmosphere comprising of 80% N 2 –20% H 2 , at 500 °C, for 5 h. The surface morphology investigated, using a scanning electron microscope (SEM) and the surface roughness was measured by use of contact method. Chemical composition was analyzed by X-ray fluorescence spectroscopy and formation of AlN phase was confirmed by X-ray diffrac- tion. The corrosion resistance of composite coatings was measured by potentiodynamic polarization in 3.5% NaCl solution. The obtained results show that plasma nitriding process leads to an increase in microhardness and corrosion resistance, simultaneously. Ó 2010 Elsevier Ltd. All rights reserved. 1. Introduction Adding ceramics and intermetallics into regular metal coatings is becoming a common method to improve surface properties like friction coefficient, wear, corrosion, oxidation, etc. Electro-deposi- tion is a well established method for fabrication of such materials because of advantages in uniform depositions on complexly shaped substrates, low cost, good reproducibility and the reduction of waste [1]. During this process, these insoluble particles are sus- pended in a conventional plating electrolyte and are captured in the growing metal film. Nickel and nickel alloys are reasonably easy to be electrodepos- ited, vastly investigated and successfully applied in several appli- cations [2]. Enhancement in different materials properties may be achieved by reinforcing metallic coating by different ceramic or metal particles. Hence effect of micro and nano sized particles such as SiC [3–6] and Al 2 O 3 [6–8], on different material properties were investigated. Other ceramics like WC [9], CeO 2 [10] and TiO 2 [11] were successfully electrodeposited and examined too. These composite coatings are of particular importance due to their in- creased microhardness and improved wear resistance. Another type of composite coating can be produced by co-deposition of metallic particles and metallic ions to fabricate electrodeposited metal matrix/metal particle composite (EMMC) coatings [12–16]. Subsequent treatment of these composite coatings may result in formation of new phases which would be difficult or impossible to produce using conventional electro-deposition methods and can improve high temperature oxidation, hardness, corrosion proper- ties, etc. Ni–Al composite coatings are one of the most popular of these composite coatings. Susan et al. [12] and Napyoszek-Bilnik et al. [13] have reported the co-deposition mechanism of Al parti- cles and the influence of operating parameters on the co-deposi- tion of these particles incorporated in nickel. Zhou et al. [15] have also reported the Al particles size effect on the microstructure of the co-deposited Ni–Al composite coatings. Earlier works re- vealed that co-deposited Al particles and heat treatment of them improved the oxidation resistance of pure Ni due to formation of Ni 3 Al phase at high temperature [17–20]. In order to improve of coating properties, the surface of electro- plated coatings can be modified by plasma nitriding. Plasma nitrid- ing is of particular interest as it is an environmentally friendly process with rather low operating temperature [21–23]. The pres- ence of a dense nitride layer on the surface cause an improvement in corrosion and wear resistance [24,25]. Diffusion of nitrogen is assisted in plasma atmosphere which in controlled conditions can bring about nitrogen rich solid solutions and nitrogen contain- ing compounds [26]. Reduced treatment gas and energy consump- tion, fewer environmental problems and formation of very low porosity single phase compound layer facilitate extension of plas- ma nitriding market in comparison with conventional gas or salt bath nitriding [27]. By plasma nitriding, aluminum particles are converted to alu- minum nitride (AlN). Aluminum nitride is a wide-band gap semi- conductor material that is finding applications in a number of technologies due to its unique combination of desirable properties such as chemical and thermal stability, low thermal expansion coefficient, and high mechanical hardness. 0261-3069/$ - see front matter Ó 2010 Elsevier Ltd. All rights reserved. doi:10.1016/j.matdes.2010.07.007 * Corresponding author. E-mail address: mahboubi@aut.ac.ir (F. Mahboubi). Materials and Design 32 (2011) 971–975 Contents lists available at ScienceDirect Materials and Design journal homepage: www.elsevier.com/locate/matdes