The influence of amplitude and current sequence on induced electrodeposition of composite layers on base of Ni-Mo alloy
Julian Kubisztal, Antoni Budniok, Jolanta Niedbała Uniwersytet Śląski, Instytut Nauki o Materiałach, ul. Bankowa 12, 40-007 Katowice
Annals 4 No. 11, 2004 pages 293-296
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abstract Ni-Mo+Mo composite coatings were prepared by co-deposition of nickel with molybdenum and molybdenum powder on a carbon steel substrate (St3S) from a citrate solution in which Mo particles were suspended by stirring. In order to obtain composite Ni-Mo+Mo layers the following plating bath was prepared: 0.035 mol/dm3 Na2MoO4, 0.75 mol/dm3 NiSO4, 0.45 mol/dm3 Na3C6H5O7 with addition of: Mo powder (150 μm, 99.9% Mo, 10 g/dm3). The suspension had a pH of 5.6÷6.0. Pulse deposition method was applied at a temperature of 293 K. The surface of composite Ni-Mo+Mo coatings was mat, porous and light-grey, irrespective of deposition current conditions. The Ni-Mo+Mo coatings exhibit good adhesion to the substrate and no internal stresses causing their cracking were observed. Surface morphology was investigated by stereoscopic microscopy. It was stated, that the porosity and development of Ni-Mo+Mo surface coatings depends on current density and the quantity of molybdenum in the coating (Figs. 2 and 3). Their chemical composition, determined by X-ray fluorescence spectroscopy method, depends on the galvanic conditions under which the coatings were obtained. Generally all Ni-Mo+Mo coatings contained from 42 to 54% wt. molybdenum (Fig. 5). The calculated thickness of the Ni-Mo+Mo coatings was about 68.7÷83.7 μm and it depends on deposition rate and the current density (Fig. 6a). The investigation of phase composition of obtained coatings shows, the presence of crystalline Mo phases built into nanocrystalline Ni-Mo matrix (Fig. 4). Key words: nickel, molybdenum, electrolytic composite coatings, pulse deposition