Influence of Target Material on the Microstructure and Properties of Ti–Si–N Coatings Prepared by r.f.-Reactive Sputtering

Abstract

We examined the effects of sputtering conditions and target materials on the microstructure and mechanical properties of Ti–Si–N coatings prepared by r.f.-reactive sputtering. We used composite targets consisting of a Ti (99.99%) plate and Si3N4 chips as well as the target consisting of a Ti plate and Si chips. Thin films were synthesized by an r.f. sputtering machine in a facing target-type (FTS) on the substrates of high speed steel. During the deposition, the substrate was heated from room temperature up to � 300 � C and a d.c. bias up to � 100 V was applied. Without substrate heating and bias, the hardness of the films increased from 30 GPa for a binary system, reaching a maximum of 37 GPa for a ternary system with a small amount (3–8 at%) of Si. It then decreased to values lower than those of binary systems when Si was more than 10 at%. The hardness of high Si films (containing � 20 at%Si) showed a lower value of 20 GPa. The hardness of high Si films deposited from the Ti–Si target increased and reached to a maximum value of 40 GPa around at a bias of � 30 V, but the crystallite size of the film increased to � 30 nm. On the other hand, the hardness of the films (containing � 20 at%Si) deposited from the Ti–Si3N4 target increased with increasing negative bias voltage, being saturated at 38 GPa over � 80 V. Although the crystallite size of the films increased gradually with increasing negative bias, it still remained at about 7 nm at � 80 V. The characteristics of the latter film could be attributed to the formation of a nano-composite structure defined