Effects of conventional and active screen plasma nitriding on properties of electroless Ni–B coating

Abstract

In the present study, the properties of nitrided electroless Ni–B coatings prepared by conventional plasma nitriding and active screen plasma nitriding were investigated. For this purpose, electroless Ni–B coatings were deposited from an alkaline bath on AISI 4140 substrates. Then, some of the prepared coatings were plasma nitrided by conventional method and the other ones by active screen method under the same conditions. Microstructure, morphology, microhardness and wear resistance of the coatings were evaluated. Based on the results, post-treatments change the amorphous as deposited coating structure to a crystalline one, which increases microhardness and wear resistance. Employing plasma nitriding treatment on the coatings results in higher microhardness and superior wear resistance than conventional heat treatment. The sputtering of iron atoms during plasma nitriding process can be the main reason for these results. In addition, active screen plasma nitriding demonstrates less surface roughness and superior wear resistance than conventional plasma nitriding.