Effect of CVD-Diamond on the Tribological and Mechanical Performance of Titanium Alloy (Ti6Al4V)

Nano-crystalline diamond and microcrystalline diamond films have been separately deposited on chemically treated titanium alloy (Ti6Al4V) substrates from methane/hydrogen (CH4/H2) gas mixture, using hot filament chemical vapor deposition technique. The coatings have architecture of Ti6Al4V/NCD and Ti6Al4V/MCD. The as grown nano-crystalline diamond and microcrystalline diamond films were characterized using high resolution scanning electron microscope and Raman's spectroscopy. The residual stresses along the surface of nano-crystalline diamond coatings and micro-crystalline diamond coatings are compressive in nature as shown by the Raman spectroscopy. Nanoindentation tests were also conducted using Berkovich nanoindenter for the purpose of measurement of hardness and elastic modulus values. The indentation depth for microcrystalline diamond coating was 65 nm, whereas for nanocrystalline diamond coating, it was 72 nm. Microcrystalline diamond and nanocrystalline diamond coatings have yielded the super-hardness of ~55 G Pa and ~38 G Pa respectively. The average coefficient of friction of microcrystalline diamond and nanocrystalline diamond coatings decrease from 0.305-0.27 to 0.068-0.053, respectively, when the load is increased from 1 N to 10 N. However, for conventional Ti6Al4V substrate the average coefficient of friction changes from 0.625 to 0.38 under the same input conditions.