The effect of nanodiamond concentration on wear behavior of nickel-boron-nanodiamond composite coatings

One of the most important finishing operations that is usually performed as the final process when producing a part is the modification of surface properties with surface engineering operations. Many metals can be coated by the electroless-coating method. Electroless nickel-boron coatings have been widely used in the industry due to their cheap price and uniform coating capability. In this article, nickel-boron-nanodiamond electroless coating with different concentrations of nanodiamond was applied on AISI 4140 steel, and its structural properties and wear behavior were investigated. The structural properties of the coatings were investigated with the help of X-ray diffraction tests, scanning electron microscopy, and hardness test. Also, the friction coefficient and wear properties of the samples were studied using the pin-on-disc test. The results show that with the increase in nanodiamond concentration, the structure of the coating changes from amorphous to semi-crystalline. In addition, the electron microscope images and the hardness test results show that adding nanodiamonds to the electroless bath increases the hardness. Adding nanodiamonds to a concentration of 0.5 g/L improved the wear resistance and reduced the friction coefficient. However, increasing the concentration of nanodiamonds up to 1 g/L due to the agglomeration of nanodiamonds caused an increase in the specific wear rate of the coating.