Effect of sonic vibration on vapour deposited coating

Abstract

This work examines how vapor deposited coating of carbon (partially diamond) on stainless steel 304 substrate is affected by the sound vibration. For this a specially designed chemical vapor deposition (thermal CVD, hot filament) apparatus having facility of generating sound vibration at different frequency is fabricated. A coating of carbon (partially diamond) has been deposited on the substrate, and the characterization of the coating has been done by SEM including EDX and XRD. The coating of carbon is identified by EDX, and the allotropic forms of graphite and diamond peaks of carbon are found by XRD analysis. By SEM analysis, it is found that the microstructures of deposited coatings are more compact and smooth"er under vibration than that in absence of vibration. The experiments were conducted under different ranges of vibration including sonic and ultra sonic range. Studies have shown that the growth rate of deposited coating on a unit area is higher under vibration than that in absence of vibration. It is found that deposition rate varies with the distance between substrate and activation (tungsten) heater and frequency of vibration. The deposition rate does not vary significantly with the change of frequency in the sonic range. The amount of deposition under ultrasonic vibration increases significantly with the frequency of vibration upto 5 - 6 mm distance between substrate and activation heater. Within this distance, the difference of deposition rate under vibration and without vibration conditions increases almost linearly with the increase of frequency of vibration. Beyond this distance, the effect of frequency on deposition rate becomes almost constant. In addition, the higher the distance thc less is the effectiveness of frequency of vibration on the deposition rate in that range. The deposition rate increases due to the extra vibration of sound added to the system which may enhance the activation energy by increasing its kinetic energy. During experiments the effects of pressure, temperature and duration on deposition rate under vibration and absence of vibration are also investigated. The experimental results are compared with those available in the literature and physical explanations are provided.