Characterization and properties of nanocrystalline diamond coatings

Diamond an allotrope of carbon and hardest substance ever known has attracted a great deal of interest in many fields of Materials Engineering, owing to its outstanding fundamental properties and technological applications. It is least compressible (~100 GPa) and has the highest known thermal conductivity of the order of 2000 Wm−1 K−1. Subsequently it has a low thermal expansion coefficient (0.8×10−6 K−1) at room temperature and is very resistant to chemical corrosion. Diamond coatings obtained by Chemical Vapor Deposition (CVD) are being excellently used in wear resistant parts for mechanical and tribological applications on account of high hardness and elastic modulus, chemical inertness and low self-friction coefficient. However, the tribological characteristics of the CVD diamond coatings are mainly influenced by the grain size and crystallinity. The Hot Filament CVD technique (HFCVD) has several advantages like uniformity over a large area, ease of operation, relatively simple set-up and adaptability to product geometries. Besides, diamond's excellent thermal conductivity acts as an additional safeguard in maintaining lower temperatures by rapidly dissipating heat.