Tribological behavior of electroless Ni-B ternary and quaternary coatings with inclusion of W and Mo

Electroless nickel coatings help to tailor requisite surface properties in materials for use in various applications. The aim of the present study is to examine the tribological behavior of electroless nickel-boron coatings incorporated with Mo and W. The coated layers are developed over pin samples with various bath compositions. The coated specimens are characterised to assess their basic features. The tribological tests are carried out with the help of a pin-on-disc tribo-tester under dry conditions. The coating characteristics are determined to comprehend the importance of tungsten as well as molybdenum concentration in electroless nickel-boron coatings. In the as-deposited state, all the coated specimens displayed a surface morphology resembling cauliflower. Moreover, the roughness of these coated surfaces in their as-deposited state showed an increase corresponding to the concentration of the bath parameter, resulting in a higher coefficient of friction (COF). The addition of Mo into Ni-B matrix promotes the coarse grained and cracked surface morphology leading to highest friction coefficient value of as-deposited Ni-B-Mo coatings. The highest surface roughness of Ni-B-Mo coatings also leads to the highest specific wear rate due to breaking and crushing of roughness peaks. The present study reveals the effect of incorporation of W and Mo in electroless Ni-B coatings to control the friction and wear characteristics of the specimens. This will help in deciding the proper electroless bath compositions for specific tribological applications.