Production of composite layers on the base of Ni-Mo alloy with larger contents of Mo
Jolanta NIedbała Uniwersytet Śląski, Instytut Fizyki i Chemii Metali, ul. Bankowa 14, 40-007 Katowice
Annals 2 No. 5, 2002 pages 369-373
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abstract The composite layers on a base of Ni-Mo alloy with larger contents of Mo were electrodeposited in galvanostatic condition. Studies were carried out in an citrate solution containing suspension of Mo powder. In order to compare Ni-Mo layers from the citrate solution not containing of Mo powder were obtained. The carbon steel (St3S) with a surface 4 cm2 was used as a substrate material. The layers were deposited in the current density range of 100 to 300 mA/cm2. The two range of kinetic changes of layers formation, distinct in Ni-Mo layers has been observed (Fig. 1). To the potential value of about 1.3V, the current deposition of Ni-Mo+Mo layers are less in comparison with current deposition of Ni-Mo layers. It may be concluded that inhibition effects occur in electrodeposition of Ni-Mo+Mo composite layers (Fig. 1). So the contents of Mo in Ni-Mo layers and Ni-Mo+Mo layers obtained in the potential range is comparable. In the case of potential values above 1.3 V, the current deposition of Ni-Mo+Mo layers is less than the current deposition of Ni-Mo layers (Fig. 1). The surface of composite layers Ni-Mo+Mo was mat, porous and light-grey, irrespective of current condition. The Ni-Mo+Mo layers exhibit good adhesion to the substrate and no internal stresses causing cracking were observed. An increase in current deposition is accompanied by an increase in surface development (Fig. 2). On the X-ray diffractograms of layers obtained at the room temperature beside the wide peaks which indicate of the presence of nanocrystalline Ni-Mo base the peak of crystalline Mo are observed (Fig. 3). In the case of Ni-Mo+Mo layers an increase in the temperature to 800oC the crystallization of the composite base is observed (Fig. 3). The Mo contents in Ni-Mo layers determined by X-ray fluorescence method is in the range of 20.70% (j = 100 mA/cm2) to 30.5% (j = 100 mA/cm2). The increase in current deposition to j = 300 mA/cm2 is accompanied by a insignificant decrease in Mo contents in the layers to 28.1%. The Mo contents in Ni-Mo+Mo layers is in the range of 57.13% (j = 250 mA/cm2) to 79.60% (j = 150 mA/cm2). An addition of Mo powder to electrolyte causes considerable increase in Mo contents in Ni-Mo layers. Based on an increase in mass of the electrode and an chemical constitution, a thickness of Ni-Mo+Mo layers has been estimated. The thickness is in the range of 65.6 to 132.6 μm and depends on the current deposition. An increase in current deposition is accompanied by an decrease in the thickness of Ni-Mo+Mo layers. The thickness of Ni-Mo+Mo composite layers is greater than thickness of Ni-Mo layers. The thickness of Ni-Mo layers is in the range of 40 to 60 μm. The rate of the layers electrodeposition depends on current density (Fig. 4). The rate of the layers electrodeposition increases with an increase in current density both in the case of Ni-Mo layers and Ni-Mo+Mo layers but the rate of Ni-Mo+Mo layers electrodeposition is greater. There was ascertained that from citrate solution (pH = 6.5÷7.5) Ni-Mo layers containing about 30% Mo and Ni-Mo+Mo layers containing about 80% Mo are obtained. The optimum current density of Ni-Mo layers electrodeposition is in the range of 0.2 to 0.3 mA/cm2. In the case of Ni-Mo+Mo layers the optimum current density is in the range of 0.1 to 0.2 mA/cm2. The rate of Ni-Mo+Mo layers electrodeposition is greater than the rate of Ni-Mo layers electrodeposition