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Oxidation of orthorhombic Ti 2 AlNb alloys at 800 °C in air
Author(s) -
Ralison A.,
Dettenwanger F.,
Schütze M.
Publication year - 2000
Publication title -
materials and corrosion
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.487
H-Index - 55
eISSN - 1521-4176
pISSN - 0947-5117
DOI - 10.1002/(sici)1521-4176(200005)51:5<317::aid-maco317>3.0.co;2-w
Subject(s) - orthorhombic crystal system , materials science , business , metallurgy , crystallography , chemistry , crystal structure
Aerospace activities as well as the power generation and automotive industries would definitely benefit from the potential weight savings and increased operation temperatures made possible by the use of orthorhombic titanium aluminides. A high effort is nowadays given in the development of these materials, based on the composition Ti 2 AlNb. They are attractive in comparison to the conventional titanium aluminides because of their good balance of specific mechanical properties at both room‐ and high‐temperatures combined with good thermomechanical processing capabilities and a very good ignition resistance. Three orthorhombic alloys with various β‐stabilising elements contents (Ti‐23Al‐25Nb‐0.35Si, Ti‐22Al‐25Nb‐1Mo‐0.2Si, Ti‐23Al‐13Nb‐5Ta‐3Mo) were investigated, with respect to their oxidation resistance in air at 800 °C. Oxidation kinetics are discussed with regard to the influence of the alloying elements. Complete scale spallation occurred after 10 × 100 h and a multilayered oxide scale of alternating TiO 2 ‐rich and AlNbO 4 ‐rich layers with segregation of the refractory elements had developed. In addition to this catastrophical scale formation, two types of subsurface morphologies were obtained, which appeared to be successive development states of the inward progress of the oxidation mechanism. The orthorhombic materials were very sensitive to interstitial diffusion leading to severe embrittlement. A third type of subsurface morphology was found together with a thin adherent alumina rich oxide scale on the Ta‐containing specimen. The protective morphology was associated with an interfacial zone of (Ti, Nb)‐nitride and (Al, Nb)‐rich metal phase. These observations and the “Ta‐effect” are discussed in consideration of the literature data.