Aug. 2009, Volume 3, No.8 (Serial No.21) Journal of Materials Science and Engineering, ISSN 1934-8959, USA 54 Enhancement of corrosion resistance of ternary Ni-W-P alloys using nanocoating ∗ Talal A. Aljohani 1 , Abdullah M. Almayouf 2 , Abdullah I. Almarshad 1 (1. Corrosion Research Group, King Abdulaziz City for Science and Technology, Riyadh 11442, Saudi Arabia; 2. Department of Chemistry, King Saud University, Riyadh 11451, Saudi Arabia) Abstract: Ternary Ni-W-P alloys deposits on carbon steel substrate were obtained by the electroless process. Nickel sulfate and sodium tungstate were used as nickel and tungsten sources, respectively, and sodium hypophosphite was used as reducing agent. Deposits were characterized for their structure, morphology, chemical composition and microhardness. A single broad peak was obtained from XRD results for ternary Ni-W-P alloys. Addition of 0.09, 0.12 and 0.15 M of tungsten in the bath has increased the peak sharpness. The grains size of the nanocrystalline deposits determined using Schererr formula and found to be around 10 nm for all alloys. The hardness was increased after addition of tungsten from 4.46 to 7.01 GPa for the lowest and highest tungsten concentrations respectively. The DC and EIS electrochemical measurements revealed that the ternary Ni-W-P alloys exhibit excellent corrosion resistance. The polarization resistance was noticeably increased. Key words: electroless Ni-W-P; nanocoating; corrosion resistance; nanocrystalline 1. Introduction Electroless coating can be divided to three main categories namely alloy coatings, composite coatings and metallic coatings [1] . Electroless nickel has gained more popularity due to its excellent properties such as high hardness, wear and corrosion resistance and has been applied to various kinds of automobile, aircraft and electronics application [2] . These properties can be further improved through the co-deposition of one or ∗ Acknowledgements: The authors acknowledge the financial support by King Abdulaziz City for Science and Technology (KACST) and acknowledge Mr. Ibrahim Mashour for valuable assistance. Corresponding author: Talal A. Aljohani (1980- ), male, Master; research field: materials corrosion and protection. E-mail: tgohani@kacst.edu.sa. two metallic elements in electroless nickel deposits. Among the metals, tungsten has a significant importance due to its high hardness and high melting point [3] . The deposition of tungsten with nickel has been of considerable interest because of enhanced physical properties of the thin film. Tungsten possesses the highest melting point (3410ºC), the lowest coefficient of linear thermal expansion, and the highest tensile strength and has unusual mechanical properties, so the addition of tungsten to Ni-P alloy deposited by electroless process improves the properties of the alloyed layer [4] . A plausible mechanism has been proposed for the deposition of ternary Ni-W-P alloys based on the assumption that nickel and tungsten form a mixed complex in solution, which act as the direct precursor for the deposition of alloys. The reactions of deposition are as follow: Ni 2+ + 2e → Ni (1) WO 4 2- + 6e + 4H 2 O → W + 8OH - (2) H 2 PO 2 - + 3OH - → HPO 3 2- +2H 2 O + 2e (3) H 2 PO 2 - + 2H + + e → P + 2H 2 O (4) Unfortunately, no direct evidence has yet presented for existence of such a complex [5] . 2. Experiment 2.1 Samples preparation The experiments were designed to deposit a thin film of Ni-W-P from electroless nickel baths. All the chemicals used in the preparation of electroless baths were analytical grade and dissolved in deionized water.