Recent advances in electroless nickel‑boron coatings

Abstract

Electroless nickel‑boron coatings have been used in various industrial sectors for more than 40 years due to their excellent mechanical and tribological properties, that exceed those of hard chrome, with homogeneous surface finishing, and competitive corrosion resistance. Standard electroless nickel‑boron coatings are usually confined to use in niche applications such as saw blades, firearms, and valves in the oil and gas industry due to the presence of heavy metals from the stabilizing agent in the coated system. However, recent advances in technology have made it possible to remove heavy metals but also to improve the productivity and properties of the coatings, sometimes in a remarkable manner. This introduces the standard EN-B coatings and their properties and highlights the most recent improvements, variants in bath composition and process and applications of electroless nickel‑boron; such as the production of lead and thallium-free coatings, the effect of ultrasonics and surfactants, composite and multi-alloy coatings, but also innovative post-treatments to provide a wide panorama of the recent advances in the field. Finally, the review brings light to the new developments that are still necessary in the field to narrow the gap between research and industrial development and enlarge the niche area of utilization. • EN-B coatings present high hardness, making them excellent candidates for the replacement of hard chrome. • Removing heavy metal stabilizer from electroless nickel-boron opens new fields of applications such as automotive. • Use of ultrasound allows increasing the plating speed of electroless nickel-boron without losing in properties. • Properties of electroless nickel-boron coatings can be tuned by using composite, multilayers, and alloy coatings. • Bath replenishment and recycling are still limited, developing methods for sustaining plating bath life is required.