Morphology and microstructure evolution of Ti-50 at.% Al cathodes during cathodic arc deposition of Ti-Al-N coatings

Abstract

Today's research on the cathodic arc deposition technique and coatings therefrom primarily focuses on the effects of, e.g., nitrogen partial pressure, growth temperature, and substrate bias. Detailed studies on the morphology and structure of the starting material-the cathode-during film growth and its influence on coating properties at different process conditions are rare. This work aims to study the evolution of the converted layer, its morphology, and microstructure, as a function of the cathode material grain size during deposition of Ti-Al-N coatings. The coatings were reactively grown in pure N 2 discharges from powder metallurgically manufactured Ti-50 at.% Al cathodes with grain size distribution averages close to 1800, 100, 50, and 10 lm, respectively, and characterized with respect to microstructure, composition, and mechanical properties. The results indicate that for the cathode of 1800 lm grain size the disparity in the work function among parent phases plays a dominant role in the pronounced erosion of Al, which yields the coatings rich in macro-particles and of high Al content. We further observed that a reduction in the grain size of Ti-50 at.% Al cathodes to 10 lm provides favorable conditions for self-sustaining reactions between Ti and Al phases upon arcing to form c phase. The combination of self-sustaining reaction and the arc process not only result in the formation of hole-like and sub-hole features on the converted layer but also generate coatings of high Al content and laden with macro-particles.

Effect of work function and cohesive energy of the constituent phases of Ti-50 at.% Al cathode during arc deposition of Ti-Al-N coatings

“…The holes observed in the converted layer of the E.M. grade (see Fig. 4) are attributed to the formation of a gamma phase with a 5.3% higher density compared to that of the Ti-Al powder [19].…”

“…Other deposition parameters include a base pressure of 2.0x10 -6 Pa, an arc current of 75 A, a substrate bias of -30 V, a constant deposition time of 10 minutes, and substrates were held stationary in front of the cathode at a distance of 15 cm. Coatings were also deposited from planar cathodes of both grades under the same parameters as above, although only with a N2 pressure of 2 Pa. To capture and follow the growth and evolution of the converted layer of both grades, smaller cathode pieces (2x1x0.5 cm 3 ) of both grades were arced with the single trigger event as described elsewhere [19]. The pieces had a mirror-like finish achieved by sequential grinding, lapping, and polishing, where the final step removes surface oxides prior to the single trigger event.…”

“…The heat modifies the surface by forming a so-called converted layer of few microns [7][8][9]. Several research papers have discussed the association and dynamics of the cathode spot with surface roughness [10,11], surface contamination [12,13], surface temperature [14], inclusions [15], steering magnetic field [16], and material properties like work function [17] and cohesive energy [18][19][20]. The significance of material properties of the cathode, e.g., work function and cohesive energy become prominent in the dynamics of the cathode spot, especially if the cathode comprises more than one phase.…”

Influence of additional dielectric coatings on the electrode surfaces on selected parameters of acoustic emission signals in high-voltage gas insulation systems

“…Artificial neural networks are also used in the analysis of AE signals [22,23]. One can notice that topics like presence of PDs in high-voltage insulation systems [24], coatings influence of arc deposition [25], improving electrical parameters with the use of nanocoatings [26] and mainly using AE method with diagnostics of high-voltage equipment [27], especially transformers [28,29], are now in the center of attention of researchers.…”

Erosion and cathodic arc plasma of Nb–Al cathodes: composite versus intermetallic

“…Furthermore, additionally to the elemental fractions of multi-element cathodes, structure and morphology of such cathodes are likely to influence cathodic arc properties. While several experiments indicate the formation of intermetallic phases in the converted layer of eroded composite cathodes [17][18][19], experiments which explicitly compare cathodic arcs from a cathode composed of an intermetallic phase to a composite cathode with the same elements and atomic ratio seem to be absent in literature, apart from a recent report by [20] in the context of arc deposition. There, the authors compared two kinds of Ti-Al cathodes with different phase compositions: pure α-Ti and Al phases versus a mixture of intermetallic Ti 3 Al and TiAl phases, both with 50 at% Al content.…”