Influence of boron doping on mechanical and tribological properties in multilayer CVD-diamond coating systems

Titanium alloy (Ti6Al4V) substrates were deposited with smooth multilayer coatings, by hot filament chemical vapour deposition technique. The effect of boron doping on lattice parameter, residual stresses, hardness and coefficient of friction in multilayer-diamond coating system was studied. The frictional behaviour of the coatings was studied using a ball-on-disc micro-tribometer by sliding the coated samples of titanium alloy (Ti6Al4V) substrates against alumina (Al2O3) balls, and increasing normal load from 1 to 10N. The average friction coefficient decreased from 0.36 to 0.29 for undoped multilayer-diamond coating system and from 0.33 to 0.18 for borondoped (BD) multilayer-diamond coating system. The average indentation depths for undoped and BD multilayerdiamond coating systems were found to be equal to ∼58 and ∼65 nm, respectively, and their hardness values were 60 and 55GPa, respectively.