Effect of CVD-diamond coatings on the tribological performance of cemented tungsten carbide substrates

Abstract

A comparison has been documented between nanocrystalline diamond (NCD) and microcrystalline diamond (MCD) coatings deposited on cemented tungsten carbide (WC-Co) substrates with architectures of WC-Co/NCD & WC-Co/MCD, using hot filament chemical vapor deposition (HFCVD) technique. In the present work, the frictional characteristics were studied using ball-on-disc type linear reciprocating micro-tribometer, under the application of 1–10N normal loads, when sliding against smooth alumina (Al2O3) ceramic ball for the total duration of 15min, under dry sliding conditions. Nanoindentation tests were also conducted using Berkovich nanoindenter for the purpose of measurement of hardness and elastic modulus values. The average coefficients of friction of MCD and NCD coatings decrease from 0.37 – 0.32 and 0.3 – 0.27 respectively, when the load is increased from 1–10N. However, for conventional WC-Co substrate the average coefficient of friction increases from 0.60–0.75, under the same input operating conditions. The wear tracks formed on the surfaces of CVD-diamond coatings and WC-Co substrate, after friction measurement were characterised using Raman spectroscopy and scanning electron microscopy (SEM) techniques. However, the compositional analysis for the formation of tribo-layer observed on the wear tracks of CVD-diamond coatings was confirmed using energy dispersive spectroscopy (EDS) technique. Therefore, maintaining an appropriate level of normal load and using appropriate type of diamond coating, friction may be kept to some lower value to improve mechanical processes.

Keywords

• Hot filament CVD
• Nanocrystalline
• Microcrystalline
• Coefficient of friction
• Wear track
• Tribo-layer