Development and characterization of Ni-B coatings with reinforcement of solid lubricant hBN

Abstract

Electroless deposition techniques can be utilized in manufacturing coatings with self-lubricating properties suitable for industrial applications. Electroless Ni-B coatings have emerged as a better alternative to electrodeposited Ni-based coatings and apart from possessing high hardness; these alloy coatings are well-known for their superior resistance to wear and abrasion. Incorporation of hBN as solid lubricating phase in electroless Ni-B alloy matrices can effectively improve its tribological characteristics. This study presents microstructural, mechanical and tribological characterizations of electroless Ni-B and Ni-B/hBN composite coatings developed on steel substrates. Microstructural features and phase compositions of the deposited coatings can be systematically studied involving FESEM and XRD analyses. Studies of deposited coatings with X-ray diffraction reveal a mixed phase amorphous/crystalline characteristic and confirms the existence of hBN in coatings’ matrix. Heat treatment of deposited samples (at 450^oC, 1hr) is performed to observe changes in structural aspects of coatings. Thorough tribological characterizations on all deposited Ni-B based coatings performed in sliding and scratch modes reveal significant improvements in frictional behaviour with the addition of hBN. Notably, annealing imparts significant changes in electroless Ni-B coatings’ structure as new diffraction peaks corresponding to crystalline nickel (Ni) and nickel boride intermetallic phases (Ni3B, and Ni2B) are noticed. Formation of these hard intermetallic phases upon heat treatment corroborates to the betterment in mechanical and tribological characteristics of deposited coatings.