Time-modulated CVD on 0.8 μm-WC–10%-Co hardmetals: study on diamond nucleation and coating adhesion

Abstract

In this study, we investigate the deposition of diamond films onto 0.8 μm-WC–10%-Co hardmetals using chemical vapour deposition (CVD). Polycrystalline diamond films were deposited using (i) constant methane (CH 4) flow, at 3 and 4.5 sccm, and (ii) modulated CH 4 flow at 4.5 sccm and 3 sccm for 8 min and 10 min, respectively. Constant flow of CH 4 into the vacuum chamber, during diamond CVD is the conventional approach to deposit diamond films onto a range of materials. The timed CH 4 modulations are an integral part of our recently proposed process, called time-modulated CVD (TMCVD). The TMCVD process increased drastically the number of diamond crystallites nucleating onto WC–Co. Furthermore, the time-modulated films exhibited (i) smooth surface profile, (ii) improved film coverage and (iii) better coating adhesion. The adhesion was characterised using conventional indentation tests. Data obtained from the micro-Raman spectroscopy technique was used to calculate the biaxial stresses. It is expected that the TMCVD process increases both the diamond nucleation processes and the coating adhesion possibly due to the secondary nucleation processes occurring during the high CH 4 bursts. It is highly likely that the mechanical interlock at the coating/substrate interface increases during the CH 4 pulse cycles.