Temperature-dependent residual stress and thermal stability studies of multilayer HF-CVD diamond coatings on RB-SiC

Abstract

Structurally graded multilayer (ML) diamond coatings were deposited on reaction bonded silicon carbide (RB-SiC) using a hot filament chemical vapour deposition (HF-CVD) system via two different routes: a continuous process (C-ML) and a three-step intermittent process (Ix-ML, x being the number of steps). In this study, the temperature-dependent residual stresses and thermal stabilities of the C-ML and Ix-ML coatings after annealing at 100° intervals from 100 °C–800 °C were investigated. Scanning electron microscopy, 2D/3D Raman mapping, cluster analysis, and sp2/sp3 ratio computations were carried out at all stages and the results were compared. The residual stresses of the as-deposited coatings, I1-ML, I2-ML, I3-ML, and C-ML, were compressive with values of −1.09 GPa, −0.90 GPa, −0.62 GPa and −1.35 GPa, respectively, which progressively shifted to the tensile regime on annealing and exhibited values of 0.50 GPa, 0.50 GPa, 0.61 GPa and 1.75 GPa respectively, after annealing at 700 °C. The sp2/sp3 ratios of the C-ML and I3-ML coatings dropped from 0.94% to 0.54% and 1.07% to 0.54%, respectively, as the annealing temperature increased from 100 °C to 700 °C. All coatings were completely oxidised at 800 °C except I3-ML, where patches of the original coating persisted even after annealing at 800 °C.