The properties of (Ti,Al)N coatings deposited by inductively coupled plasma assisted d.c. magnetron sputtering

Abstract

(Ti,Al)N coatings were deposited on M2 high speed steel substrates by inductively coupled plasma (ICP) assisted d.c. magnetron sputtering, and the structure and mechanical properties such as hardness, Young's modulus, wear resistance and adhesion strength were investigated. A TiAl alloy target (Ti/Al — 50:50 at.%) was sputtered in an Ar and N 2 atmosphere with 400 W for d.c. magnetron power as well as 400 W for ICP power at 80 mtorr of working pressure. Both the hardness and adhesion strength of the coating were found to increase with increasing substrate bias voltage. The hardness value was higher than 6500 HK 0.01 at the bias voltage higher than –50 V. The Young's modulus of the coating had a maximum value of approximately 450 GPa at −50 V. The wear properties of coatings also improved with the application of the substrate bias voltage. It was found that the grain size decreased (<100 nm), and the columnar structure, which was observed in the absence of bias, disappeared when a bias voltage was applied. The high hardness and good wear property was attributed to the microstructure change from a columnar structure with facet shaped grains to a denser one with small and round shaped grains.