Effect of boron carbide reinforcement on surface properties of electroless Ni-B and Ni-B-W coatings

Today, composite coating of nickel-boron with an electroless method is considered as an innovative, attractive, and trend topic. It is known that the hardness and tribological properties of electroless nickel-boron (EN-B) coating can be improved with co-deposition of ceramic particles. In this study, boron carbide (B4C) was added to binary (Ni-B) and ternary (Ni-B-W) EN-B coatings: (i) Ni-B-B4C, and (ii) Ni-B-W-B4C. Surface morphology, phase structure, tribological characteristics, and electrochemical behaviors for all coatings were investigated and compared. The surface morphology of composite coatings was transformed from cauliflower to cloudy-shaped with the addition of B4C particles. Characteristic amorphous structure with some degree of crystallinity was obtained at all types of coatings. Experimental test results revealed that the boron carbide particles provide a noticeable enhancement in hardness. The hardnesses of composite coatings were improved by approximately 52% in Ni-B-B4C and 62% in Ni-B-W-B4C compared to EN-B coatings. Boron carbide reinforcement and poly-alloying with tungsten caused an increase of hardness at Ni-B from 673 HV0.025 up to around 1096 HV0.025 (Ni-B-W-B4C) which is a noticeable increase in hardness. With boron carbide addition binary and ternary coatings wear factors showed a discernible diminishment by several times. Besides, electrochemical analyses indicated a minimal decrease in the corrosion resistance of composite coatings compared to that of Ni-B and Ni-B-W coatings.