Preparation and properties of Ni–Co–P/nano‐sized Si₃N₄ electroless composite coatings

Abstract

Ni-Co-P/nano-sized Si 3 N 4 composite coating was successfully fabricated on aluminum alloys by electroless plating in this work. The surface and cross-sectional morphologies, composition, microstructure, microhardness, friction and wear behavior of deposits were investigated with SEM, EDS, XRD, Vickers hardness and high-speed reciprocating friction, respectively. It was found that a Ni-Co-P/nano-sized Si 3 N 4 composite coating on aluminum alloy substrate is uniform and compact. The existence of nano-sized Si 3 N 4 particles in the Ni-Co-P alloy matrix causes a rougher surface with a granular appearance, and increases the microhardness but decreases the friction coefficients and wear rate of electroless coatings. Meanwhile, the effects of heat treatment at 200, 300, 400 and 500 C for 1 h on the hardness and tribological properties were researched. It is revealed that both of the microhardness and tribological properties of Ni-Co-P coatings and Ni-Co-P/Si 3 N 4 composite coatings increase with the increase of heating temperature in the range of 200-400 C, but show different behavior for the two coatings after annealing at 500 C.

Electroless Nanocomposite Coatings: Synthesis, Characteristics, and Applications

“…To achieve a better wear resistance, it is necessary to ensure (i) a high number density of nanoparticles, (ii) uniform distribution, (iii) better integrity between the nanoparticles and the Ni-P matrix, and (iv) heat treatment to impart a high hardness and to present an incompatible surface for the counterface material during wear. The tribological performance of EL Ni-P nanocomposite coatings incorporated with CNTs/ MWCNTs [6][7][8]12], Si 3 N 4 [23], SiO 2 [42], Al 2 O 3 [25], HNT [18], WS 2 [20], and WC [15] nanoparticles confirms the above attributes.…”

“…If nanoparticles could act as nucleation sites, then one would expect an increase in the rate of deposition. Hu et al [23] have reported that addition of Si 3 N 4 nanoparticles to EL Ni-Co alloy plating bath has increased the number of catalytic active sites and increased the rate of deposition from 4.2 to 5.6 mm. Addition of TiN nanoparticles, however, has caused a decrease in the deposition rate from 11 to 5 mm [21].…”

“…The entrapment of particles in EL Ni-P matrix is likely to influence the roughness of the resultant coating. Incorporation of Si 3 N 4 nanoparticles in EL Ni-Co-P matrix has increased the average surface roughness from 0.235 mm (for particle-free EL Ni-Co-P coating) to 0.658 mm [23]. However, incorporation of CNTs in the EL Ni-P matrix has led to a decrease in the average roughness from 192 to 129 nm (assessed using atomic force microscopy at a 14 mm  14 mm scale) [12].…”

“…Subsequently, the nanoparticle suspension is added to the EL plating bath. This procedure is widely used for many types of nanoparticles, viz., SiC [13,14], WC [15], TiO 2 [16], Al 2 O 3 [17], halloysite nanotubes [18], ZrO 2 [19], WS 2 [20] TiN [21], TiC [22] Si 3 N 4 [23] diamond [24], etc. Besides CNTs, ball milling is also considered as a pretreatment for other nanoparticles.…”

Electroless Plating of Ni-P-W Coatings Containing Scattered Nb2O5 on Sintered NdFeB Substrate

“…It has been reported that the Ni-P coatings prepared by electroless plating have some outstanding mechanical and chemical properties, such as good corrosion resistance, wear-resistance and high microhardness etc. 4,5 . On the other hand, the electroless plating has the advantage of its ability to coat interior surfaces of pipes, valves, and other parts.…”