Scratch and Sliding Wear Testing of Electroless Ni–B–W Coating

Abstract

Electroless Ni–B–W coating is deposited on low carbon steel in an alkaline sodium borohydride-reduced electroless bath. The mechanical and tribological properties of such coatings are much necessary to be assessed to carry out application-based studies. The present work focuses mainly on the evaluation of hardness and fracture toughness of electroless Ni–B–W coatings using a scratch tester. Coating's response toward scratching is also studied thoroughly. The characteristic short-range order present in its lattice structure causes the generation of a specific behavioral pattern. Furthermore, a linear sliding wear test is carried out on coatings' surface to analyze the wear behavior at different loading conditions. The specific wear rate is observed to be minimum at a normal load of 22.5 N against Si3N4 counterbody. The patterns of tribological behavior of the coating at different load values are examined from the worn surface morphologies. But before embarking on the scratch and sliding wear tests, the synthesized coatings are characterized under field emission scanning electron microscope and X-ray diffraction in an exhaustive manner. The growth rates with respect to time and the changes in morphological aspects of the coating are also evaluated. The present study establishes electroless Ni–B–W deposits as a suitable option for protecting mechanical components against wear.

Tribo-mechanical behaviour of electroless Ni-B-Mo coatings with varying bath composition

“…The coating's hardness and elastic modulus are improved upon heat treatment within 300 °C to 450 °C with the formation of Ni 2 B, Ni 3 B phases [21,22]. The binary alloy coatings are developed along with different elements such as Mo, W and investigated the coating characteristics [19,[23][24][25][26][27][28].…”

Co-deposition of W and Mo in electroless Ni–B coating and its effect on the surface morphology, structure, and tribological behavior

“…The amorphous hump was also observed for mid-B Ni–B-based coatings in other research works where the Ni (111) peak was surrounded by a broad dispersive peak. 7,17,18,32,33 Also, it may be noted here that the XRD results indicate that the B content in the coatings lie in the mid-B range, i.e. within ∼4–7 wt%.…”

“…The top surface nodule formation and cauliflower-like appearance takes place through nucleations of nano-grains, which initiates at the peaks or valleys of surface profile and then grows along the lateral direction. 17,29 A similar phenomenon results in the formation of the globular cauliflower-like morphology of the binary and poly-alloy coatings.…”

“…Dense and homogenous growth of colonies of nodules was also observed for Ni–B–W coatings by Nemane and Chatterjee. 17 The Ni–B–Mo-coated surface (Figure 2(c)) typically resembles the surface of a cauliflower with the formation of aggregates of a cluster of nodules. This is similar to the observation made by Serin and Göksenli 18 where Ni–B–Mo coatings were seen to form agglomerates of nickel that formed clusters and was casually distributed.…”

“…Besides heat/thermo-chemical treatment or nitriding, recent studies have revealed that an inclusion of a third or fourth element to form poly-alloys enhances the properties of the coatings. 16–24 The inclusion of tungsten resulted in the formation of the Ni–B–W coating, 16,17 while the inclusion of molybdenum resulted in the deposition of the Ni–B–Mo coating. 18,19 A significantly higher microhardness of Ni–B–W coatings were observed compared to the binary alloy.…”