A comparative investigation of mechanical and tribological properties of multilayered CVD-diamond coatings: effect of boron doping

Abstract

In the present work, smooth boron-doped (BD) and undoped multilayered diamond coating systems (MDCS) with top layer nanocrystallinity were deposited on chemically etched cemented tungsten carbide (WC-6%Co) substrates, using hot filament chemical vapour deposition (HFCVD) technique. Both coatings were accomplished by combining the alternate thin films of microcrystalline diamond (MCD) and nanocrystalline diamond (NCD) with a transition layer (TL) of ~1μm thick, using predetermined process parameters during the deposition process. The effects of boron doping on the residual stresses (σ), hardness (H) and coefficient of friction (COF) of MDCS were analyzed using Raman spectroscopy, Berkovich Nanoindenter and Micro-tribometer, respectively. The comparison has been documented between BD-MDCS with undoped one, under same input operating conditions and within same atmospheric conditions. The frictional characteristics were studied under the application of increasing normal load when sliding against smooth alumina (Al2O3) ceramic counter ball for the total duration of 20 min, within dry sliding conditions. The average values of COF of undoped-MDCS and BD-MDCS decrease from ~0.30 – 0.27 and ~0.28 – 0.25, respectively under the application of 1 – 10 N loads. Also, the average values of indentation depths for undoped-MDCS and BD-MDCS were ~65 nm and ~70 nm, with average hardness values in the range of ~65 – 80 GPa and ~55 – 75 GPa, respectively. Therefore, depositing smooth, adhesive and thick BD-multilayered diamond coatings on cemented tungsten carbide components would certainly enable its many useful future applications in mechanical industry.