The present paper describes the study of the synergism between the matrix microstructure and reinforcement phase in electrodeposited nanocomposite coatings. Adding hard nanoparticles into the metallic matrix leads to hardening of the coating. The effects of particle load, size and dispersion on hardening as well as their influence on metal microstructure refinement were studied. The relative contributions of strengthening factors in Ni/nano-SiC composites, namely, Hall–Petch strengthening, Orowan strengthening, enhanced dislocation density and particles incorporation, were evaluated. The production of various coatings under different stirring conditions and powders resulted in dissimilarities in the incorporation of particles. The Hall–Petch relationship for pure nickel was determined using samples produced under different current densities. Additionally, the grain refinement resulting from the particle codeposition and agitation mode were identified as influential factors in grain-size strengthening. Dislocation density strengthening was significant in electrodeposits produced using ultrasonic agitation, while it was negligible in layers produced under other conditions. Particles codeposition affected the magnitude of Orowan strengthening, resulting in cases where strengthening was negligible despite the presence of particles. The sum of contributions and the modified Clyne methods were used to calculate the hardness of the composites based on the contribution of each strengthening factor, and the calculation results were in good agreement with experimental data. The wear behavior of the composites was analyzed by pin-on-disk measurements, and the results correlated with the strengthening mechanisms. Particle size, dispersion and content increased the strengthening effects as well as the hardness and wear resistance of the coatings. Graphical abstract

This study analysed the influence of the codeposition of SiC particles with different sizes: 50 nm, 500 nm and 5 μm, and the type of bath agitation (stirring or ultrasonic) on the electrocrystallisation of nickel coatings. The composites matrix microstructure was analysed by means of SEM, EBSD and XRD, to evaluate the grain size, crystal orientation, and internal stresses and was benchmarked against pure nickel samples electrodeposited in equivalent conditions. The codeposition of nano- and microsize particles with an approximate content of 0.8 and 4 vol.%, respectively, caused only a minor grain refinement and did not vary the dominant < 100 > crystal orientation observed in pure Ni. The internal stress was, however, increased by particles codeposition, up to 104 MPa by nanoparticles and 57 MPa by microparticles, compared to the values observed in pure nickel (41 MPa). The higher codeposition rate (11 vol.%) obtained by the addition of submicron-size particles caused a change in the grain growth from columnar to equiaxial, resulting in deposits with a fully random crystal orientation and pronounced grain refinement. The internal stress was also increased by 800% compared to pure nickel. The ultrasound (US) agitation during the deposition caused grain refinement and a selective particle inclusion prompting a decrease in the content of the particles with the larger particles. The deposits produced under US agitation showed an increase in the internal stresses, with double values compared to stirring. The increase in the deposits microhardness, from 280 HV in pure Ni to 560 HV in Ni/SiC submicron-US, was linked to the microstructural changes and particles content. Graphical abstract

This work has explored the potential of using pulse reverse (PR) plating for increasing the deposited fraction of SiC nanoparticles. Two PR waveforms were selected, a short pulse (500 Hz) waveform and a newly modified and adapted pulsed sequence that equals the plating thickness to the particles’ diameter (50 nm) for the on-time and half-diameter during the anodic time. The pulse waveforms were designed with 4 and 10 A⋅dm⁻² as the average current density and cathodic peak current density, respectively. Direct current (DC) deposits at the same values were also produced as reference. In all cases, the codeposition of nano-SiC particles influenced the microstructure. The electroplating under DC 10 A⋅dm⁻² showed the strongest grain refinement and increased the content of the particles (up to 2% vol.) PR using high-frequency achieved a similar codeposition. The maximum particle incorporation was achieved by the proposed adapted pulse waveform, doubling the SiC content produced by other set-ups (up to 4% vol.); increasing the microhardness of the deposits to 400 HV, despite no grain refinement compared to the pure metal. From these results, it was observed a relationship between the influence of the plating method on the microstructure, the particle content, and the material's hardness.

This work explores the surface protection against wear provided by electroplated metal matrix composite coatings containing hard and lubricant particles. The second phase mix was selected to provide wear resistance by hardening the material and decreasing the friction coefficient. In this study, the capacity of providing wear protection by nano-SiC and self-lubrication by submicron graphite was addressed. Nickel-based composites with a dual powder mix of SiC 60 nm and graphite 400 nm, combined on a 10:10 g L⁻¹ ratio, were produced by electrocodeposition. In addition, to better understand their synergy, mono-composites with SiC 60 nm or Graphite 400 nm with a powder load of 10 g L⁻¹ were also produced. Pure nickel was also electrodeposited under the same conditions as a benchmark. Electron backscatter diffraction (EBSD) maps and chemical composition analysis were used to correlate the results from microhardness, wear resistance, and friction to the microstructure and particle incorporation rate. The wear rate tested by pin-on-disc decreased when the codeposition fraction and microhardness increased. Three main factors were determined to contribute to the coating hardness: Intrinsic hardness of the particle type, strengthening by grain refinement, and dispersion strengthening. The composites containing SiC provided the best wear protection due to the highest microhardness and grain refinement.

This work focuses on the significance of the particle’s residence time in composite electrodeposition. Ni-SiC were produced using different pulse-reverse (PR) waveforms based on the average particle diameter (60 nm). The waveform was designed to deposit a metal thickness equivalent to the average diameter during the cathodic pulse and strip half during the anodic pulse. The shape of the waveform was modified to study its effect on particle codeposition by changing the cathodic and anodic pulse current density peaks and cycle time while maintaining the same charge. For benchmark, samples were also produced under direct current (DC), matching the cathodic pulse current density peaks and average. The electrodeposition was done in an additive-free and SDS-Watts bath. ζ -potential measurements were employed to determine the interaction between particles and electrolyte. A relation was established between particle incorporation rate and residence time at the electrode interface, examining. The microhardness of the deposits was also studied. The SiC content was more than doubled by PR compared to DC, from 2 vol.% to 5.5 vol.% even after SDS addition. The increase in codeposition rate was related to the anodic pulse time, supported by the existing models on the mechanisms of particle codeposition.