Arc Evaporation of Ti–Al–Ta–N Coatings: The Effect of Bias Voltage and Ta on High-temperature Tribological Properties

Abstract

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.

XPS and AFM Investigations of Ti-Al-N Coatings Fabricated Using DC Magnetron Sputtering at Various Nitrogen Flow Rates and Deposition Temperatures

“…Properties of Ti-Al-N are strongly dependent on their chemical composition [7,8]. The Al content in Ti-Al-N coatings overcomes the oxidation problems, but a superficial Al 2 O 3 layer formed at high temperature [9][10][11].…”

Properties of multilayered and multicomponent nitride alloys from first principles

“…The 0 K thermodynamics of quaternary transition metal nitride (Ti-Al-X-N, X=Zr,Hf,V,Nb,Ta) alloys has recently been investigated by Holec using ab initio simulations [86]. Zr improves the oxidation resistance and the as deposited hardness of Ti 1−x Al x N [87,88]; Hf leads to an inferior oxidation resistance of Ti 1−x Al x N and promotes the formation of cubic domains, however it retards the formation of stable wurtzite AlN during thermal annealing [89,90]; The addition of V to Ti 1−x Al x N hard coatings enables lubricating effects based on oxidation resistance and improves the overall wear resistance [91][92][93]; Nb and Ta are also favored due to combining outstanding mechanical properties with good oxidation resistance [94][95][96].…”

Progress in development of coated indexable cemented carbide inserts for machining of iron based work piece materials

“…The PVD TiAlN coatings were alloyed with Ta as described elsewhere [12,13]. The CVD TiCN coatings consists of a TiN interlayer (0.7 µm), a medium temperature TiCN layer (5.8 µm) [14], a bonding layer and corundum type α-Al 2 O 3 layer in 0001 texture (3.5 µm).…”