Effect of Negative Substrate Bias Voltage on the Microstructure and Mechanical Properties of Nanostructured Ti–Al–N–O Coatings Prepared by Cathodic Arc Evaporation

Abstract

Ternary Ti–X–N coatings, where X = Al, Si, Cr, O, etc., have been widely used for machining tools and cutting tools such as inserts, end-mills, and etc. Ti–Al–N–O coatings were deposited onto silicon wafer and WC-Co substrates by a cathodic arc evaporation (CAE) technique at various negative substrate bias voltages. In this study, the influence of substrate bias voltages during deposition on the microstructure and mechanical properties of Ti–Al–N–O coatings were systematically investigated to optimize the CAE deposition condition. Based on results from various analyses, the Ti–Al–N–O coatings prepared at substrate bias voltage of -80 V in the process exhibited excellent mechanical properties with a higher compressive residual stress. The Ti–Al–N–O (-80 V) coating exhibited the highest hardness around 30 GPa and elastic modulus around 303 GPa. The improvement of mechanical properties with optimized bias voltage of -80 V can be explained with the diminution of macroparticles, film densification and residual stress induced by ion bombardment effect. However, the increasing bias voltage above -80 V caused reduction in film deposition rate in the Ti–Al–N–O coatings due to re-sputtering and ion bombardment phenomenon.