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Recently, titanium aluminium tantalum nitride (Ti-Al-Ta-N) coatings have been shown to exhibit beneficial properties for cutting applications. However, the reason for the improved behaviour of these coatings in comparison to unalloyed Ti-Al-N is not yet clear. Here, we report on the tribological mechanisms present in the temperature range between 25 and 900°C for this coating system, and in particular on the effect of the bias voltage during deposition on the tribological response. Based on these results, we provide an explanation for the improved performance of Ta-alloyed coatings. An industrial-scale cathodic arc evaporation facility was used to deposit the coatings from powder metallurgically produced Ti 40 Al 60 and Ti 38 Al 57 Ta 5 targets at bias voltages ranging from -40 to -160 V. X-ray diffraction experiments displayed a change with increasing bias voltage from a dual-phase structure containing cubic and hexagonal phases to a single-phase cubic structure. Investigations of the wear behaviour at various temperatures showed different controlling effects in the respective temperature ranges. The results of dry sliding tests at room temperature were independent of bias voltage and Ta-alloying, where the atmosphere, i.e. moisture and oxygen, were the most important parameters during the test. At 500°C, bias and droplet-generated surface roughness were identified to determine the tribological behaviour. At 700 and 900°C, wear depended on the coating's resistance to oxidation, which was also influenced by the bias voltage. In conclusion, Ta-alloyed coatings show a significantly higher resistance to oxidation than unalloyed Ti-Al-N which could be an important reason for the improved performance in cutting operations.

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