Preparation and characterization of Ni–Cu–P/CNTs quaternary electroless composite coating Wu Yucheng a, * , Ren Rong a , Wang Fengtao a , Yuan Zaoshi a , Wang Tugen a , Hu Xiaoye b a School of Materials Science and Engineering, Hefei University of Technology, Hefei 230009, China b Key Laboratory of Materials Physics, Institute of Solid State Physics, Chinese Academy of Sciences, Hefei 230031, China Received 9 July 2007; received in revised form 24 January 2008; accepted 1 February 2008 Available online 23 February 2008 Abstract Ni–Cu–P/carbon nanotubes (CNTs) quaternary composite coatings were successfully obtained on low carbon steel matrix by electroless plating. The effects of CNTs concentration in the bath on the microstructure of the composite coatings, CNTs content in the composite coatings and the hardness of composite coatings before and after heat treatment at 400 8C have been studied. In addition, the corrosion resistance of Ni–Cu–P/CNTs composite coatings was evaluated by anodic polarization curves in 3.5 wt.% NaCl solution at room temperature. It was noted that the CNTs concentration remarkably influenced the surface morphology of the coatings. With increasing CNTs concentration, both the CNTs content in the composite coatings and the hardness of composite coatings increased at first and then decreased. And the composite coatings after heat treatment provided higher hardness than the as- deposited coatings. The corrosion resistance of Ni–Cu–P/CNTs composite coatings is excellent compared with that of Ni–Cu–P coatings. # 2008 Elsevier Ltd. All rights reserved. Keywords: A. Surfaces; B. Chemical synthesis; D. Mechanical properties; D. Microstructure 1. Introduction Recently, carbon nanotubes (CNTs) are getting more and more attention for their excellent characteristics after their discovery by Iijima [1]. CNTs have great potential for composite reinforcement application due to their exceptional mechanical and physical properties such as high strength, elastic modulus, flexibility, unique conductivity and reduced friction [2–7]. Several studies have reported on the preparation and performances of CNTs-reinforced electroless composite coatings with improved wear resistance, hardness and decreased friction coefficient, including Ni/CNTs and Ni–P/CNTs composite coatings [8–10]. In addition, CNTs can also be used to prepare the composites with promising electrochemical properties due to their chemical stability. Ni–Cu alloys with Cu content around 30 wt.% are highly corrosion resistant under corrosion environments such as in halide solution like seawater. Due to these attractive features, a variety of attempts have been made to plate Ni–Cu www.elsevier.com/locate/matresbu Materials Research Bulletin 43 (2008) 3425–3432 * Corresponding author. Tel.: +86 551 2905085; fax: +86 551 2901152. E-mail address: ycwu@hfut.edu.cn (W. Yucheng). 0025-5408/$ – see front matter # 2008 Elsevier Ltd. All rights reserved. doi:10.1016/j.materresbull.2008.02.019