Tribo-Mechanical Characterisation of Borohydride Reduced Ni–B

Tribo-Mechanical Characterisation of Borohydride Reduced Ni–B–W Coatings

Barman, Manik / Barman, Tapan Kumar / Sahoo, Prasanta

The borohydride reduced electroless coatings are widely used for their excellent tribological, physical and mechanical behaviours. The coating behaviours are dependent on its compositions. The addition of hard particles into Ni–B matrix may alter the coating composition and ultimately lead to modification in coating behaviours. Hence, electroless Ni–B–W coatings were developed on AISI 1040 steel substrate to understand the significance of tungsten concentration in tribo-mechanical behaviour of the W reinforced ternary coatings. The surface roughness of the coating was seen to increase significantly with sodium borohydride concentration though the surface roughness is lower (0.185) at lower concentrations of sodium borohydride relative to substrate (0.285). But the roughness values did not vary much with nickel chloride concentration as well as sodium tungstate. The SEM results of as-coated specimens reveal the cauliflower-like surface morphology which is useful for the reduction in friction and wear of the coatings. The elemental analysis results obtained from EDAX show an increase in tungsten concentration from 2.8 to 4.2% with the increase in bath level concentration leading to increase in surface hardness obtained from nano-indentation technique and the scratch hardness obtained from micro-scratch tests. The nano-hardness and scratch hardness were also observed to improve with nickel chloride, sodium borohydride concentration in the coating bath solution.