Effect of carbon nanotubes concentration on wear resistance of nickel-boron-carbon nanotubes coatings

In the present study, nickel-boron-carbon nanotubes coatings were deposited in AISI 4140 steel substrate by varying carbon nanotubes concentration, and then the structure and wear behavior of the coatings were taken into investigation. The structure of the coatings was studied through XRD, SEM, and microhardness tests. Additionally, the wear behavior of the samples was evaluated using pin on disk method, and the worn surface of the samples was studied by SEM and EDS analysis. Results indicated that by increasing carbon nanotubes concentration the crystallographic structure of the coatings changes from amorphous to semi-crystalline. Moreover, SEM images of the samples and microhardness results indicated that increasing carbon nanotubes concentration increases surface microhardness and lead to higher coating thickness. Increasing carbon nanotubes concentration up to 0.6 gr/lit increased the wear resistance, and decreased the coefficient friction. However, increasing carbon nanotubes concentration up to 1 gr/lit increased the wear rate of the coating which was due to agglomeration of carbon nanotubes.