Electrochemical and structural properties of electroless Ni-P-SiC nanocomposite coatings

Synthesis and properties of electrodeposited Ni–B–CeO2 composite coatings

Nickel–phosphorus (Ni–P) coatings with controllable P content and desirable characteristics can be produced by tuning bath chemistry and processing conditions during the electroless process. Although pure medium- and high-P coatings offer a good combination of mechanical and corrosion properties, their performance attributes can be further enhanced through incorporation of silica (SiO2) nanoparticles. Using 15 and 30 g/L of sodium hypophosphite as reducing agent in the plating bath, Ni–P coatings with respective P content of 10.8 and 14.3 wt.% were produced. While the surface roughness and grain size increased with an increase in the P content, the average hardness value and corrosion resistance of medium-P coatings were superior to their high-P counterparts. The average hardness of the Ni–P– SiO2 coatings based on medium-P Ni–P matrix was determined to be ~ 11.0 GPa. Electrochemical impedance spectroscopy (EIS) studies of these coatings indicated area-impedance values on the order of 108 Ω·cm2, whereas the double-layer capacitance per unit area (Cdl) and charge transfer area-resistance (Rct) values, computed from theoretical fit of the EIS data, were in the range of 1.18 × 10− 10 F·cm− 2 and 3.14 × 108 Ω·cm2, respectively. The findings confirmed that addition of SiO2 nanoparticles modifies deposit morphology through grain refinement, reduction in the surface roughness and minimization of surface porosity in the nanocomposite coatings.

Influence of SiO2 nanoparticles on hardness and corrosion resistance of electroless Ni–P coatings

Properties of electrodeposited Ni–B–Al2O3 composite coatings

Homogeneous nickel-phosphorus-silica (Ni-P-SiO 2 ) nanocomposite coatings were prepared on low carbon steel alloy surfaces by a new process. This method was developed by combining sol-gel and electroless deposition technique in the presence of surfactant to produce a composite coating containing well-dispersed SiO 2 nanoparticles. The SiO 2 -sol solution was directly added to the electroless Ni-P solution to produce nanocomposite coating on the St37 steel substrate. The surface morphology and composition analysis were studied by scanning electron microscopy (SEM) and energy dispersive X-ray spectrometer (EDS), which confirmed the presence of silica in the coating matrix. The results showed co-deposited SiO 2 nanoparticles with a clean surface and no agglomeration. Therefore, this technique can effectively avoid the agglomeration of nanoparticles in the coating matrix. The structural phase analysis indicated that by heat treating, the amorphous phase changed to crystalline phases such as Ni, Ni 3 P and some non-equilibrium phases. The microhardness and wear properties of Ni-P and Ni-P-SiO 2 composite coatings were evaluated and compared with each other. The hardness and wear resistance of Ni-P composite coatings increased in the presence of SiO 2 nanoparticles, whereas the maximum microhardness of 970 Hv 100 , minimum coefficient of friction of 0.25, and minimum wear loss of 4.4 mg were achieved in heat treated coating at 400 °C for 1 h.

Improvement in tribological behavior of novel sol-enhanced electroless Ni-P-SiO2 nanocomposite coatings

Highly homogeneous Ni–P/SiO2 nanocomposite coatings were prepared by electroless deposition from composite baths containing well dispersed SiO2 nanoparticles. The particle concentration in the coatings increases gradually with the SiO2 concentration in the bath and reaches an observed maximum of 25 vol.% at a bath concentration of 10 g/l. Tribological measurements of the heat treated coatings indicate that while the hardness of the coating is decreased compared to that of the Ni–P coating without particles, an improvement in Pin-on-Disk wear resistance up to a factor of 2 can be achieved. The aspect ratio of the wear track of samples heat treated above 270 °C is found to increase with the concentration of nanoparticles in the coatings. This observation indicates that the nanoparticles also modify the wear behavior of the coatings.

Homogeneous electroless Ni–P/SiO2 nanocomposite coatings with improved wear resistance and modified wear behavior

The present invention provides novel metal coatings containing Nickel and Silica-particles of 10 - 400 nm size as defined in the specification; workpieces containing such coatings; electroless nickel plating baths suitable for producing such coatings and workpieces; processes for manufacturing such plating baths and coatings / workpieces.

Peter Fehr

Papers

Homogeneous electroless Ni–P/SiO2 nanocomposite coatings with improved wear resistance and modified wear behavior

Electroless nickel plating containing silica nanoparticles