An Ni/nanodiamond composite coating was deposited on carbon steel in a traditional Watt’s solution without additives via direct current (DC) electroplating. The effects of the nanodiamond concentration and current density in the plating solution on the morphology, grain size, and texture of the Ni/nanodiamond composite coating were observed using X-ray diffraction (XRD) and scanning electron microscopy (SEM). The distribution of the nanodiamond particles in the composite coating was investigated by Raman spectra and SEM. The mechanical properties of the composite coating, such as its elastic modulus and hardness, were examined using a Nano Indenter XP nanometer mechanical test system. The coefficient of friction was tested using a Universal Micro-Tribotester. The results demonstrated that the preferential orientation of the Ni/nanodiamond composite coating varied from the (111) crystal orientation of the pure nickel coating to the (200) crystal orientation. When the nanodiamond concentration in the plating solution was 8.0 g/L and the current density was 3.0 A/dm², the hardness of the composite coating reached the maximum value of 5.302 GPa and the friction factor was maintained at around 0.1. The average grain size of the composite coating was reduced to 20.4 nm.

The electrodeposition process parameters were optimized for the acquisition of high-strength monolithic nickel layers on Q235A substrates based on the Watts nickel plating solution using the DC electrodeposition method. Based on the study of the electrochemical polarization behavior of nickel ions in Watts’ plating solution, 16 experimental protocols were selected according to the orthogonal test method. The residual stress, microhardness, modulus of elasticity, and surface roughness of the nickel plating were tested by X-ray diffractometer, nano-mechanical test system, and surface profilometer, respectively, to investigate the influence of current density, temperature, and PH on the mechanical properties of nickel plating, so as to determine the best process solution for the preparation of high-strength nickel plating. The results of the study show that the mechanical properties of the nickel deposits electrodeposited onto Q235A are optimized when plating at a current density of 3 A/dm², a bath temperature of 45 °C, and a pH of 3.5. The nickel-plated layer has a minimum grain size of 34.8 nm, a microhardness of 3.86 GPa, a modulus of elasticity of 238 GPa, and a surface roughness Ra of 0.182 μm.

Ni-based composite coating containing nanodiamonds was deposited on the substrate of Q235A low-carbon steel in a traditional Watts solution, without any additive. The nanodiamond grains prepared by detonation synthesis were measured by Transmission electron microscope (TEM) and X-ray diffraction (XRD). The electrochemical behavior of Ni²⁺ ion in the composite bath including nanodiamonds was studied by linear sweep voltammetry experiments, and the morphology, elastic modulus, and hardness of Ni-based composite coating were characterized using Scanning Electron microscope (SEM) and the nano-indenter XP tester. Effects of the nanodiamond concentration in the bath, stirring speed, and the electroplate mode on the properties of Ni-based composite coating were investigated. The results show that the reduction of Ni²⁺ ion in the electroplating process increased initially, and then decreased as the nanodiamond concentration in the bath increased from 4 g/L to 16 g/L, irrespective of whether direct current (DC), single-pulse, or double-pulse electroplating mode was used. The highest over-potential could be obtained when the nanodiamond concentration in the bath was 8 g/L. Moreover, the hardness and elastic modulus of the composite coating prepared by the DC electroplating mode were 4.68 and 194.30 GPa, respectively. By using the same plating parameters, the coating prepared by the double-pulse electroplating mode showed better properties, with hardness and elastic modulus values of 5.22 and 197.38 GPa, respectively.