*3.3.1. Materials and methods*

Ni-P-SiC electrodeposits were obtained from a modified Watts Ni bath (containing 0.2 M NaCl, 0.65 M NiSO4⋅6H2O, 0.75 M NiCl2⋅6H2O, 0.1 M H3BO3, 0.1 M H3PO3 [36]) + 0.084 mM DTAB + 0.02 g mL-1 SiC, with a pH of 1.5 adjusted with 1 M HCl) (solution S1). These solutions were prepared immediately prior to each experiment using deionized water (18 MΩ cm) and analytical-grade reagents of the highest purity available (Sigma-Aldrich).

The Ni-P-SiC coatings were obtained via electrodeposition of solution S1 under galvanostatic conditions. The coatings were then annealed in air for 60 min at one of four temperatures: 300 °C, 400 °C, 500 °C, or 600 °C.

An atomic force microscope (AFM) (Digital Instruments, Mod. Nanoscope E) was used in contact mode to image the deposited Ni-P-SiC on the steel substrate. These measurements were performed in air (ex situ) using silicon nitride AFM tips (Digital Instruments). All images were obtained at 2 Hz and are represented in the so-called height mode, in which the highest portions appear brighter.

The deposited phases were identified via X-ray diffraction (XRD) using a Bruker diffractometer (Mod. D8 Advance) (Bragg-Brentano arrangement) with CuKα radiation (λ = 1.54 Å). The range of 2θ from 40° to 95° was recorded at a rate of 0.2° s-1.

The elemental composition of the coatings as a function of the thickness was obtained using a glow discharge spectrometer (GDS) (Leco, Mod. 850A).

Hardness was measured with a Matsuzawa MXT-ALFA Vickers microhardness tester with a 10-g load applied for 15 s. The final value quoted for the coating hardness was the average of ten measurements.

Wear tests were performed on a reciprocating ball-on-disk tribometer (CSM tribometer) in air at a temperature of approximately 25 °C and a relative humidity of approximately 39% under dry, nonlubricated conditions. Balls (3 mm diameter) made of AISI 8620 with a hardness of 25 HRC were used as the counter body in the wear tests. All wear tests were performed under a 2-N load at a sliding speed of 1 cm s-1. The friction coefficient and the sliding time were automatically recorded during the test. The wear volume was measured according to the ASTM G99 standard method. Three wear tests were conducted for each sample.
