Influence of surfactants on the tribological behaviour of electroless Ni?P coatings

Wear and scratch behaviour of electroless Ni-P-nano-TiO2: Effect of surfactants

Abstract: This paper investigates the effects of surfactants on microhardness, scratch, wear and friction behaviour of the Ni-P-nano-TiO 2 composite coatings. Nano TiO 2 particles were co-deposited with electroless Ni–P coating on low carbon steel substrates in the presence of anionic and cationic surfactants-sodium dodecyl sulphate (SDS) and dodecyl trimethyl ammonium bromide (DTAB) respectively. Results revealed that at an optimum concentration of the surfactants, the coatings obtained a smoother surface, low frictional coefficient, enhanced microhardness and high wear resistance. The findings of scratch test showed that the composite coatings with surfactants exhibited the ability to withstand higher critical load and lower penetration depth. This can be ascribed to the reinforcing action of co-deposited TiO 2 nanoparticles in the composite coatings. The cationic surfactant DTAB contributed to the increase in weight percentage of TiO 2 in the Ni–P matrix considerably. At critical micelle concentration (CMC) value of the DTAB surfactant, the coatings had the highest weight percent of incorporated TiO 2 and showed a better homogenous distribution.

Estimation of Zwitterionic Surfactant Response in Electroless Composite Coating and Properties of Ni–P–CuO (Nano)Coating

Abstract: Electroless Ni–P and Ni–P–CuO coating on mild steel was developed successfully with the addition of Zwitterionic surfactant. The usage of nano-CuO in electroless coating was intermittent though the cost is low with high catalytic activity. Zwitterionic surfactant was introduced into the composite coating for the first time to increase the suspension of nanoparticles effectively during the coating process. Surfactant helps to reduce the intermolecular attraction between the solid and liquid interfaces and hence binding of nanoparticles with the hydrogen gas bubbles was eliminated. Also agglomeration of nanoparticles was controlled by stirring the electrolyte continuously using magnetic stirrer. The characterization and tribological properties were tested for the newly developed composites. Scanning electron microscope micrograph reveals the deposits are produced without any defects and the presence of CuO nanoparticles in the deposit. Energy-dispersive spectroscopy measurement shows the changes of weight percentage of elements available in the substrate. The surface roughness of the deposit was improved with the addition of CuO, it packs the gap between two grains and offers smooth finish and as the result the surface properties are modified. Microhardness of the substrate was improved for the substrate added with nano-CuO. The corrosion resistance of the substrate was improved when compared to the substrate produced using electroless Ni–P binary coating. Zwitterionic surfactant reduces the agglomeration of nanoparticles during chemical reaction and allows the particles to coat only on the target. Similarly, this technique can be implemented in the production of other composites in electroless coatings.

Effect of zwitterionic surfactant on tribological behaviour of electroless plating

Abstract: Zwitterionic surfactant consisting of positive and negative charges on its head is introduced in electroless alkaline bath to reduce the cost of electroless plating in industrial applications. The concentration of surfactant varied from 0 to 0·030 g L−1 insteps of 0·006 g L−1. The surfactant exhibits attractive and repulsive forces in the electrolyte used, and their corresponding influence on coating thickness, surface structure, adhesion, specific wear rate and microhardness was studied. The results indicated that there was an improvement in the properties of coated substrate. Scanning electron microscope image showed a unique blackberry shaped surface structure after adding the surfactant. Without zwitterionic surfactant, the coating thickness was 44·31 μm, and with surfactant at 0·018 g L−1, it was increased to 98·03 μm. The wear resistance of coated substrate was improved to 54% when compared with the substrate coated without surfactant. Without addition of surfactant, the microhardness was 43...

A new method to prepare MgO and base for further electroless nickel deposition on magnesium substrate

Abstract: The present research uses the safer hydrogen halide to prepare the MgO-MgI2/MgBr2 layers onto AZ91 magnesium alloy in alkaline solution. The water-soluble metal salts (MgI2/MgBr2) were not responsible for the corrosion protection; whereas Mg(OH)2 formed first and then converted to MgO by heat-treatments and this MgO was responsible for the corrosion protection. The electrochemical results showed that the development of MgO mitigated the corrosion process and improved the corrosion resistance. This new treatment was then used as a pre-treatment for further electroless nickel (EN) deposition and it showed the good corrosion current density and better corrosion potential on the magnesium substrate. This new treatment and EN depositions were characterised by XPS and SEM. The electrochemical polarisation and EIS test of these EN depositions were evaluated in 3.5 wt.% NaCl. In addition, pitting behaviour of these EN depositions were evaluated by linear sweep voltammetry test.

Wear and corrosion resistance of electroless Ni-P- ZnO - SiO2 nanocomposite coatings on magnesium AZ91D alloy

Abstract: In this work, wear and corrosion behavior of the electroless Ni-P- ZnO-SiO2 of nanocomposite coatings with concentrations as follows (0.5-0.5),(1-1),(1.5-1.5),( 2-2) g/L were developed on AZ91D magnesium alloy. Surface morphology and elemental analysis were carried out by Optical microscope (OM) and scanning electron microscopy (SEM) coupled with Energy-dispersive X-ray spectroscopy (EDAX). Wear and corrosion resistance were determined by pin-on-disc apparatus, and salts spray method. SEM was used to study wear mechanisms of coated magnesium alloy. The low specific wear rate of 1.3964x105mm3/Nm of ZnO-SiO2 was at (1.5-1.5)g/L which showed a better wear resistance to other nano-coated samples follows. The corrosion rate at (1.5-1.5)g/L showed a lower rate of 0.000265 MPY compared to other nano co-deposits. The co-deposits ZnO-SiO2 with optimum concentration ZnO-SiO2 at (1.5-1.5)g/L can be for nickel-phosphorus matrix composite nanocoatings for enhanced wear and corrosion resistance.

Studies on crystallization of electroless NiP deposits

Abstract: Electroless Nickel-Phosphorus deposits with phosphorus content of 4.35, 5.45, 6.80, 8.10 and 9.12 Wt.% P were made, on mild steel substrates. The deposits were annealed at 60, 100, 200, 300, 330, 360, 400 and 600°C for 2 hours. The crystallization process of these deposits was studied using X-ray line profile analysis, differential scanning calorimetry and microhardness. The X-ray diffraction pattern of all the deposits indicated the presence of crystalline and amorphous phases coexisting in the as deposited condition. The lattice disorder in the crystalline phase increased with increasing phosphorus content. Profile refinement techniques have been used to separate the crystalline nickel (111) reflection from the amorphous profile. The separated (111) and (222) profiles of nickel were used for crystallite size and microstrain analysis. The crystallite size of nickel was found to vary from 50A in the as deposited condition to about 600A in the fully annealed state (400°C). The crystallite size increased sharply above 300°C, indicating the onset of precipitation. The microhardness values showed typical precipitation hardening type of behavior, increasing from an initial value of about 450 VHN in the as deposited state to the peak hardness of about 825 to 950 VHN, corresponding to a temperature range of 360 to 400°C. Differential scanning calorimetry of these deposits, indicated only one major reaction between 325 to 375°C. Ni 3 P has been identified as the final stable precipitate at 600°C.