High Temperature Oxidation Behaviour of Tial8Nb Alloy

Abstract

The goal of this work is to determine the effect of niobium on the kinetics and mechanism of Ti-Al oxidation in air. In order to compare the oxidation kinetics of Ti-Al and Ti-Al with the addition of niobium, isothermal oxidation was performed on Ti-48Al and Ti-46Al-8Nb (in at.%) alloys at 1073 K in synthetic air. Cyclic oxidation of Ti-46Al and Ti-46Al-8Nb alloys was carried out in laboratory air for 42 cycles (1 cycle, 24 hrs). The morphology, as well as chemical and phase composition of the oxidation products were investigated using X-ray Diffraction (XRD) and Scanning Electron Microscopy combined with Energy Dispersive Spectroscopy (SEM-EDS). From these investigations it can be concluded that niobium addition increases the corrosion resistance of TiAl and, furthermore, improves the adherence between the metallic substrate and the oxide scale. The oxidation mechanism of Ti-46Al-8Nb was studied via secondary neutral mass spectroscopy (SNMS) after two-stage isothermal oxidation (24 hrs in 16 O 2 followed by 24 hrs in 18 O 2 ) at 1073 K. From this analysis it can be assumed that the oxidation mechanism of Ti-46Al-8Nb alloy consists of simultaneous outward titanium and aluminum diffusion and inward oxygen transport.Keywords: intermetallics, titanium aluminide, niobium, oxidationCelem pracy jest określenie wpływu dodatku niobu na kinetykę i mechanizm utleniania stopu TiAl w powietrzu. Dla porównania kinetyk utleniania stopu Ti-Al oraz stopu z dodatkiem niobu zostały przeprowadzone badania izotermicznego utleniania stopów o składach Ti-48Al i Ti-46Al-8Nb (w at.%) w powietrzu syntetycznym w 1073 K. Stopy Ti-48Al i Ti-46Al-8Nb poddano cyklicznemu utlenianiu w powietrzu laboratoryjnym w 1073 K obejmującym 42 cykle 24-godzinne. Morfologię oraz skład fazowy i chemiczny produktów utleniania badanych próbek przeprowadzono metodą dyfrakcji promieniowania rentgenowskiego (XRD) oraz skaningowej mikroskopii elektronowej (SEM) w połączeniu z metodą dyspersji energii promieniowania rentgenowskiego (EDS). Na podstawie tych badań stwierdzono, że dodatek niobu w stopie TiAl podwyższa jego odporność korozyjną a ponadto polepsza przyczepność zgorzeliny do rdzenia metalicznego. Mechanizm utleniania stopu Ti-46Al-8Nb badano metodą spektrometrii masowej rozpylonych cząstek neutralnych (SNMS) po dwuetapowym izotermicznym utlenianiu (pierwszy etap w 16 O 2 przez 24 godz., kolejny w 18 O 2 przez 24 godz.) w 1073 K. Na podstawie tej analizy postuluje się, że mechanizm utleniania stopu Ti-46Al-8Nb odbywa się w wyniku równoczesnej odrdzeniowej dyfuzji tytanu i glinu oraz dordzeniowego transportu tlenu.

Air oxidation behaviour of standard PVD and novel HIPIMS coatings at 750°C for 1000 h

“…Decomposition of TiN, additionally accelerates degradation of the exposed material, due to the further development of non-protective TiO 2 phase and due to release of free N 2 . In contrast to present study, Przybylski et al 19 found that TiN formed in Ti46Al8Nb alloy under isothermal oxidation at 800°C in synthetic air.…”

“…In contrast to present study, Przybylski et al 19 found that TiN formed in Ti46Al8Nb alloy under isothermal oxidation at 800uC in synthetic air.…”

“…The formation of layered poor, non-protective oxide scale on TiAl based intermetallic was described by many researchers. 1–7,12,19…”

“…The formation of layered poor, non-protective oxide scale on TiAl based intermetallic was described by many researchers. [1][2][3][4][5][6][7]12,19 Al 2 Au system Figure 10 shows a comparison of the Al-Au phase diagram reported by Okamoto, 20 Liu et Al. 21 and Li et al 22 The coating system used in this study contained Al 65 and Au 35 at-% respectively in deposited state.…”

High-temperature oxidation behavior of a cast Ti-47.5Al-2.5V-1.0Cr-0.2Zr alloy

“…These factors all affect the oxidation resistance, however, no systematic studies have been carried out in terms of oxidation kinetics, spalling form and delamination characteristics of oxide film. Studies into the oxidation of TiAl alloys are helpful in understanding the oxidation resistance of the alloy, and, at the same time, suitable means of oxidation resistance can be found according to the oxidation degree of the alloy during the oxidation process [10][11][12] . Therefore, further research regarding the oxidation behavior of the TiAl alloy becomes more urgent.…”