Origin of high temperature oxidation resistance of Ti–Al–Ta–N coatings

Abstract

a b s t r a c t a r t i c l e i n f o Keywords: TiAlTaN AlTiN Anatase Rutile Oxidation kineticsAlloying Ti-Al-N coatings with Ta has proven to enhance their hardness, thermal stability, and oxidation resistance. However, especially for arc-evaporated Ti-Al-Ta-N coatings only limited information on the detailed influence of the elements on various properties is available. Therefore, we have developed arc-evaporated Ti 1−x−y Al x Ta y N coatings with various Al (x = 0.50-0.65) and Ta (y = 0.00-0.15) contents. While the thermal stability of our coatings during annealing in inert He atmosphere increases with increasing Ta content, best results are obtained for specific Ta-Al ratios during oxidation. Single phase cubic Ti 0.32 Al 0.60 Ta 0.08 N yields a mass-gain of only~5% after 5 h at 950°C in synthetic air, whereas Ti 0.35 Al 0.65 N is completely oxidized after 15 min. This is in part based on the suppressed anatase and direct rutile TiO 2 formation at a defined Ta-Al content. Consequently, the anatase-to-rutile transformation, generally observed for Ti 1−x Al x N, is absent. This reduces the generation of pores and cracks within the oxide scale and especially at the nitride-oxide interface, leading to the formation of a protective rutile and corundum based oxide scale. This is also reflected in the pronounced decrease in activation energy for the protective scale formation from 232 kJ/mol for Ti 0.35 Al 0.65 N down to 14.5 kJ/mol for Ti 0.32 Al 0.60 Ta 0.08 N. Based on our results we can conclude that especially phase transformations within the oxide scale need to be suppressed, as the connected volume changes lead to the formation of cracks and pores.

High temperature behavior of functional TiAlBSiN nanocomposite coatings

“…which have proven to have excellent properties for industrial applications in the cutting and stamping tool industry [1][2][3]. In general, the increasing industrial demand for advanced coating systems with tailored properties, such as high hardness, good abrasive, sliding wear resistance, high temperature stability, as well as oxidation and corrosion resistance, have motivated researchers to continuously develop new quaternary and multinary based coating systems with exceptional combinations of functional properties [4][5][6]. The thermal stability of the majority of the hard protective coatings produced so far is relatively low, with a maximum operation temperature of approximately 1000°C [7].…”

“…The oxidation resistance of protective coatings gradually increases from binary compounds such as TiC (~400°C) and TiN (~650°C), ternary compounds: TiAlN (~850°C) and TiSiN (~1000°C), to quaternary compounds: TiAlTaN (~850°C) and TiAlSiN (~800°C), TiAlBN (~900°C) and recently multielement compounds such as TiAlCrYN (~930°C), CrAlSiBN (~1200°C) and TiAlSiCN (~1300°C), due to the doping of Ti-X-(N/B/C) coating with suitable X element (X = V, Al, W, Si, C, B, etc.) and also, because of their changes in nanocrystalline structure [5,[11][12][13][14]15,16,17,18]. However, the nanostructure can be considered a metastable phase, which means that when the operating temperature exceeds certain temperature, the nanostructure changes, specially grain size increases and amorphous phases crystallize within the coating layer.…”

Galling phenomena in metal forming

“…Results from load-scanner tests at an elevated temperature of 400 ℃ reveal that large h-BN powder size and low h-BN concentration can help [55]. Ti-Al-N coatings with Ta have proven to enhance hardness, thermal stability, and oxidation resistance; however, by optimizing the chemical composition of x alloyed Ti1-xAlxN coatings, the oxidation resistance can be significantly improved, resulting in a much wider range of applications [56].…”

Chemical Bonding Analysis in Ti1-x-yAlxTayN Solid Solutions

“…36 Finally, one of the most promising alloying element is Ta, which allows not only significant enhancing of the hardness, toughness and oxidation resistance of Ti 1−x Al x N coatings, but also increasing the temperature of formation of the AlN wurtzite phase up to 1200 • C, which ensures maintaining high hardness values up to this temperature. 32,[37][38][39] It is well-known that the properties of the multicomponent solid solutions strongly depend even on small variations of the relative content of the constituting chemical elements. 32 To a large extent this is due to the changes in the electronic structure and chemical bonding of the transition metal nitrides caused by variations of their elemental composition.…”

“…32 To a large extent this is due to the changes in the electronic structure and chemical bonding of the transition metal nitrides caused by variations of their elemental composition. Despite the numerous experimental and theoretical investigations of the mechanical properties, 32,35,40 solar selective characteristics, 41,42 oxidation behavior, 32,38,43 biocompatibility 44,45 and thermodynamic stability [46][47][48][49] of different ternary and quaternary TiN-based solutions, the quantitative analysis of the evolution of chemical bonding of these materials at an ab initio level was not thoroughly addressed. In the present paper, within density functional theory (DFT) calculations, we examine the evolution…”