A Novel Method to Deposit Vanadium Carbide Interlayer on Tool Steel Substrate Applied to Mitigate CVD Diamond Thermal Stresses

This work shows considerable advance in combining the exceptional properties of chemical vapor deposition (CVD) diamond with the toughness of steel, a subject that has been sought since the early 1990s. Combining both the previously developed techniques for vanadium carbide (VC) deposition, namely laser cladding vanadium carbide (LCVC) and thermo-reactive deposition (TRD) in a salt bath, made it possible to achieve the deposition of a CVD diamond film on a D6 tool steel, with a very low stress level of 1.8 ± 0.1 GPa. This was the lowest value for growth at 750 °C substrate temperature. The LCVC step was a fast processing to thicken the VC layer, while the short-term TRD (only 1 hour) closed the cracks left in the LCVC coating, relieved the residual stresses resulting from the rapid solidification after the laser incidence, and promoted a phase transformation from V₈C₇ to V₆C₅, a phase with lower thermal expansion coefficient. Hot Filament Chemical Vapor Deposition (HFCVD) was used to perform the CVD diamond deposition. The vanadium carbide layer has been an intermediate layer capable of acting as an excellent diffusion barrier and able to satisfactorily mitigate the thermal stress of the CVD diamond. The samples were characterized by Scanning Electron Microscopy with Field Emission Gun (FEG-SEM) equipped with Energy-Dispersive X-ray Spectroscopy (EDS), X-ray diffractometry, Rockwell A (588.6 N) indentation tester. Raman spectroscopy was used to further characterize HFCVD diamond, to compute the thermal compressive stress.