Investigation of the effect of boric acid addition to bath composition on the properties of nickel coatings deposited from nickel sulfamate baths

Nickel electroplating has long been recognized as one of the most versatile and widely implemented surface modification technologies in modern materials engineering. Its core principle involves the electrodeposition of a nickel layer onto a conductive substrate through an electrolytic process. This relatively simple yet highly controllable method enables the formation of metallic coatings that can drastically improve the surface properties of engineering materials without compromising their bulk mechanical characteristics. Over the last century, this technique has evolved from being a decorative coating method into a technologically indispensable process that underpins critical components across multiple industries. In automotive and aerospace engineering, for instance, nickel plating is utilized to impart enhanced wear resistance and fatigue performance to lightweight steels and alloys. In electronics and micro-manufacturing, nickel deposits are prized for their solderability, corrosion protection, and dimensional precision. In marine and energy-related sectors, their role as protective barriers against harsh corrosive environments has been indispensable. This breadth of applications underlines the importance of continuously refining electroplating chemistries and parameters to meet ever-increasing industrial demands. One of the most striking features of nickel electroplating lies in its ability to engineer the surface–substrate interface. Low carbon steels, such as AISI 1020, represent a family of materials that, while affordable and mechanically reliable, remain inherently susceptible to surface degradation phenomena such as corrosion, abrasion, and oxidation. Their intrinsic advantage excellent machinability, weldability, and plasticity render them ubiquitous in structural and mechanical contexts. However, their limited durability in aggressive environments poses challenges for high-performance service life. Nickel electroplating presents itself as an effective solution to overcome these limitations. By depositing a controlled nickel layer, the steel surface is endowed with greater hardness, refined tribological properties, and an extended resistance to corrosive agents, all while preserving the favorable mechanical attributes of the steel's interior structure. Among the several available electrolyte formulations, nickel sulfamate baths have gained prominence due to their ability to yield coatings with superior microstructural qualities. In comparison to the conventional Watts bath, sulfamate-based electrolytes are associated with deposits that exhibit lower internal stress, excellent ductility, and strong adhesion to the substrate. These features are particularly vital when coatings are intended for precision parts, where dimensional integrity must be preserved without the risk of warping or embrittlement. Additionally, nickel sulfamate baths permit higher current densities, thereby accelerating deposition kinetics and enabling the formation of thick, coherent coatings in shorter processing times. The industrial relevance of such electrolytes is further amplified by their compatibility with a wide variety of metallic substrates and their proven record in producing coatings with fine-grained, compact structures. Despite these advantages, the performance of nickel sulfamate electrolytes can be significantly influenced by bath additives. Boric acid (H₃BO₃), in particular, has historically been recognized as a buffering agent that stabilizes the local cathodic pH during electroplating. Its function extends beyond pH control: boric acid reduces the deleterious effects of hydrogen evolution—a side reaction that can lead to porosity, microcracking, and inhomogeneous deposits. By moderating hydrogen generation and forming weak complexes with nickel ions, boric acid plays a role in nucleation control and grain refinement. Consequently, its presence in the electrolyte directly influences coating density, mechanical performance, and resistance to environmental degradation. While conventional literature has noted its role in Watts baths, fewer systematic investigations have been carried out on nickel sulfamate systems, particularly in relation to low carbon steels like AISI 1020. The present research was therefore designed to address this knowledge gap. Electroplating experiments were conducted using nickel sulfamate baths, in which boric acid concentration was systematically varied to investigate its role in tailoring coating properties. The experimental matrix incorporated six boric acid levels (0, 5, 10, 20, 40, and 60 g/L) across three deposition temperatures (30 °C, 45 °C, and 60 °C). A constant current density of 4 A/dm² and a deposition time of 40 minutes were applied to maintain consistency. The choice of AISI 1020 steel as a substrate was deliberate, reflecting its industrial relevance as a cost-effective material in mechanical and structural engineering, yet one whose durability critically depends on surface enhancements. A comprehensive suite of characterization techniques was deployed to evaluate the deposited nickel coatings. Scanning Electron Microscopy (SEM) was employed to observe surface morphology and microstructural uniformity. Energy Dispersive Spectroscopy (EDS) provided insights into elemental distribution and confirmed the incorporation of nickel as the dominant phase. X-ray Diffraction (XRD) was applied to determine crystallographic orientation and to identify the potential formation of nickel boride phases, which are known to impart hardness. Mechanical assessments were conducted via Vickers microhardness testing under a 0,1 kg load, offering quantitative comparisons across the different bath conditions. Tribological performance was examined with a Taber abrasion tester, which simulated mechanical wear under controlled loading. Finally, corrosion resistance was assessed using ASTM B117 salt spray testing, providing a standardized evaluation of protective performance under chloride-rich conditions. The results demonstrated a strong and consistent influence of boric acid on the coating characteristics. Coating thickness was found to increase proportionally with boric acid concentration, ranging from as low as 6.1 µm at 0 g/L to 26 µm at 60 g/L. Hardness values exhibited a similar trend, rising from 176 HV₀.₁ in the absence of boric acid to 357 HV₀.₁ at the highest tested concentration. Microstructural analysis confirmed that coatings produced without boric acid were irregular, porous, and prone to defects such as pinholes and surface roughness. In contrast, coatings prepared with higher boric acid levels displayed smoother, denser morphologies, with fine-grained structures indicative of improved nucleation dynamics. XRD characterization offered further insights into the mechanism of performance improvement. In addition to the expected nickel peaks, the presence of Ni₃B phases was identified in samples deposited at higher boric acid concentrations. The formation of these intermetallic compounds is significant, as they contribute directly to grain boundary strengthening and microstructural stabilization, thereby enhancing hardness and wear resistance. The correlation between microstructure and property improvements was also validated through wear testing. Taber abrasion results revealed that coatings produced in boric acid-deficient baths suffered from substantial mass loss and severe wear tracks, while those from 40 g/L and 60 g/L conditions demonstrated remarkable wear resistance, characterized by minimal weight reduction and smoother wear scars. Corrosion behavior further highlighted the role of boric acid. Samples deposited without or with minimal boric acid additions exhibited early onset of red rust, blistering, and surface oxidation in salt spray tests. Conversely, samples obtained from baths containing 40–60 g/L boric acid showed no visible corrosion damage even after extended exposure, underscoring the dense and coherent nature of the deposits. This performance is attributed to the suppression of microstructural defects, improved passivation, and the formation of more uniform nickel matrices. Taken together, these observations confirm that boric acid concentration exerts a more pronounced influence on coating performance than other studied parameters such as bath temperature, which had a relatively secondary effect. In conclusion, this study provides systematic evidence that the incorporation of boric acid into nickel sulfamate baths significantly enhances electroplated coatings on AISI 1020 steel. Its effects manifest through multiple pathways: stabilization of local cathodic pH, suppression of hydrogen evolution, facilitation of uniform nucleation, and promotion of secondary hardening phases such as Ni₃B. These mechanisms collectively yield coatings with superior thickness, hardness, wear resistance, and corrosion durability. The results not only confirm the essential role of boric acid but also offer valuable guidance for industrial plating practices, where optimized bath compositions can deliver cost-effective performance improvements. Looking ahead, the findings suggest promising avenues for further investigation. Future research could extend to synergistic effects of boric acid with other bath additives, such as saccharin or organic brighteners, which are known to influence deposit stress and brightness. Moreover, the application of post-deposition treatments—such as heat treatment or laser surface modification—may unlock additional functionalities in nickel sulfamate coatings. By integrating electrochemical optimization with advanced surface engineering strategies, it is conceivable to extend the applicability of low-cost steels like AISI 1020 into domains that demand higher levels of performance. Ultimately, the present work contributes to both the scientific understanding and the industrial advancement of nickel electroplating, underscoring the transformative potential of bath chemistry optimization in surface engineering. Beyond its immediate scientific contributions, the outcomes of this study hold significant implications for industrial practice. The demonstrated ability of boric acid to improve coating density, mechanical performance, and corrosion resistance indicates that nickel sulfamate plating can be optimized in a manner that reduces production costs while simultaneously enhancing product reliability. Industries such as automotive and aerospace, where component longevity and performance are directly tied to safety and economic efficiency, stand to benefit particularly from these findings. Furthermore, the results suggest that similar approaches could be extended to other low carbon steels and alloys, enabling broader adoption of nickel electroplating as a sustainable surface engineering solution. By systematically controlling bath chemistry, manufacturers can achieve higher quality coatings without resorting to more expensive alloying or complex post-treatment techniques, thereby reinforcing the role of electroplating as a cost-effective yet technologically advanced method of surface enhancement.