Isothermal oxidation behavior of powder metallurgy beta gamma TiAl–2Nb–2Mo alloy

• Published in: Intermetallics 2011-10, Vol.19 (10), p.1509-1516
• Main Authors: Kim, D.J., Seo, D.Y., Saari, H., Sawatzky, T., Kim, Y.-W.
• Format: Article
• Language: English
• Subjects: A. Titanium aluminides; Alloy powders; Aluminides; B. Oxidation; Beta; C. Powder metallurgy; D. Microstructure; G. Aero-engine components or aerospace constructional uses; Intermetallics; Oxidation; Titanium base alloys; Titanium compounds; Titanium dioxide
• ISSN: 0966-9795; 1879-0216
• DOI: 10.1016/j.intermet.2011.05.027

A new TiAl–2Nb–2Mo beta gamma alloy was synthesized by powder metallurgy process. HIP’ed and vacuum heat treated specimens were isothermally oxidized at 800 °C and 900 °C in air up to 500 h. The TiAl–2Nb–2Mo alloy oxidized parabolically up to 500 h at both 800 °C and 900 °C. The oxides consisted of outer TiO2 layer, intermediate Al2O3 layer, and inner TiO2 rich mixed layer and the oxidation mechanisms of the alloy were identical at both temperatures. During oxidation, the degradation of lamellar colonies formed a diffusion zone just below the oxide/substrate interface consisting of γ-TiAl matrix and dispersed beta phases which contained high concentration of Nb and Mo. The oxidation rate of the TiAl–2Nb–2Mo alloy is more sensitive to temperature than those of the Ti–48Al–2Nb–2Cr and Ti–48Al–2Nb–2Cr–W alloys. [Display omitted] ► PM beta gamma TiAl–2Nb–2Mo alloy forms Ti and Al oxides at 800 °C and 900 °C. ► TiN phase forms at the oxide/substrate interface owing to the nitrogen effect. ► Diffusion zone formed by degradation of lamellar colonies containing beta phases. ► Weight gain curve obeys the parabolic law at 800 °C and 900 °C up to 500 h.