Effects of plasma nitriding on properties of electroless Ni-B coating

In this study, the properties of nitrided electroless Ni-B coating prepared by conventional plasma nitriding (CPN), were compared with those of annealed one. For this purpose, electroless Ni-B coatings were deposited from an alkaline bath on AISI 4140 substrates. Then some of the prepared coatings were annealed under controlled atmosphere and the other ones were plasma nitrided at the same conditions. Microstructure, morphology, microhardness and wear resistance of the coatings were evaluated. Based on the results, under the experimental conditions, plasma nitriding increases surface roughness; meanwhile, it improves wear resistance and microhardness of the coatings. The sputtering of iron atoms during CPN process could be the main reason for these results.