Residual stress analysis by different bias voltage of DLC films on AISI 4050 alloy steel

Abstract

Thin films are one the best choice to improve materials properties. Instead of entire replacement of the material in a component, which may be expensive, a coating process is a good option to achieve required properties precisely where they are required. Generally, coating depends on deposition methods which consist of chemical or physical interactions to form a film on substrate surface. Residual internal stresses are generated during cooling stage after deposition process, due to always present difference in thermal expansion coefficient of film and substrate materials. These stresses produce either failure or performance reduction on component utilization. Raman spectroscopy was used to evaluate these residual stresses. In this work Raman spectrum behavior was analyzed under different residual stress conditions of DLC films deposited on molybdenum doped alloy steel substrates. The comparative method used at three different bias tensions of -550, -650 and -750 V showed that residual stress increases with increasing bias voltage. The normal compressive load to produce delamination in scratching test decreased from 16 N to 9 N with bias voltage increase from -550 V to -750 V, as expected due to higher interface stresses.