Effect of target frequency, bias voltage and bias frequency on microstructure and mechanical properties of pulsed DC CFUBM sputtered TiN coating

Pulsed magnetron sputtering is well known since early 1990s for offering high process stability, improved coating quality, higher plasma density and high bias current. Target frequency, bias voltage and bias frequency are the three major influencing process parameters during deposition. In the present study, TIN was deposited on M2 grade high speed steel by pulsed DC closed-field unbalanced magnetron sputtering (CFUBMS) technique, over a wide range of above mentioned process parameters. The microstructure of the coating was analysed using field-emission scanning electron microscopy (FESEM) and high resolution transmission electron microscopy (HRTEM) and phases were detected using grazing incidence X-ray diffraction (GIXRD) technique. The mechanical properties, like adhesion and microhardness of the coating were assessed by scratch adhesion test and Vickers microhardness test respectively. The inter-diffusion phenomenon between the coating and the substrate was studied using depth profile secondary ion mass spectrometry (SIMS). The coating microstructure obtained from FESEM revealed that the deposition rate increased as well as column width reduced with increase of target frequency up to 150 kHz. The reduction in column width was more prominent with increase of negative bias voltage up to - 70 V. Scratch and hardness test indicated that adhesion and composite microhardness of the coating increased with increase of target frequency up to 200 kHz. However, both were at first increased and then decreased with increase of negative bias voltage. With increase of bias frequency, adhesion of the coating was found to improve with almost no edge spallation. However, no specific trend between coating microhardness and bias frequency could be obtained. Unlike some previous reports, with increase of bias frequency, average substrate ion current during pulse-on period was found to marginally decrease. However, the same during ion etching was noted to increase with increase of bias frequency. (C) 2010 Elsevier B.V. All rights reserved.