Microstructural observations on the oxidation of [gamma][prime]-Ni[sub 3]Al at high oxygen partial pressure

Journal Article · Fri Apr 01 04:00:00 EST 1994 · Acta Metallurgica et Materialia; (United States)

DOI:https://doi.org/10.1016/0956-7151(94)90166-X· OSTI ID:5051407

Schumann, E; Ruehle, M ^[1]

---

1. Inst. fuer Werkstoffwissenschaft, Stuttgart (Germany). Max-Planck-Inst. fuer Metallforschung

The oxidation behavior of [gamma][prime]-Ni[sub 3]Al in air has been studied by transmission electron microscopy (TEM). [gamma][prime]-Ni[sub 3]Al single crystals (surfaces parallel to (001)) were oxidized and cross-sections were prepared for TEM examination. After 1 min oxidation simultaneous formation of an external NiO scale and internal oxidation of [gamma][prime]-Ni[sub 3]Al were observed. The internal oxide particles were identified as [gamma]-Al[sub 2]O[sub 3], which possesses a cube-on-cube orientation relationship with respect to the Ni matrix. After 6 min oxidation a continuous [gamma]-Al[sub 2]O[sub 3] scale has formed between the internal oxidation zone (IOZ) and the [gamma][prime]-Ni[sub 3]Al single crystal. Oxidation for 30 min resulted in a microstructure similar to the 6 min oxidation, but the Ni in the two-phase zone has been oxidized to NiO. Oxidation for 50 h resulted in a scale consisting of an outer layer of NiO, an intermediate layer of NiAl[sub 2]O[sub 4] and an inner layer of Al[sub 2]O[sub 3]. The spinel must have formed by a solid state reaction between NiO and [gamma]-Al[sub 2]O[sub 3]. The [gamma]-Al[sub 2]O[sub 3] in the inner Al[sub 2]O[sub 3] layer transforms to the thermodynamically stable [alpha]-Al[sub 2]O[sub 3]. A crystallographic orientation relationship exists between both modifications of Al[sub 2]O[sub 3], whereby (0001)[1[bar 1]00][sub [alpha][minus]Al[sub 2]O[sub 3]][parallel](111)[1[bar 1]0][sub [gamma][minus]Al[sub 2]O[sub 3]], i.e. close packed planes and close packed directions of [alpha]-Al[sub 2]O[sub 3] are parallel to the close packed planes and close packed directions in [gamma]-Al[sub 2]O[sub 3].

• OSTI ID: 5051407
• Journal Information: Acta Metallurgica et Materialia; (United States), Journal Name: Acta Metallurgica et Materialia; (United States) Vol. 42:4; ISSN 0956-7151; ISSN AMATEB
• Country of Publication: United States
• Language: English

Related Subjects

36 MATERIALS SCIENCE
360105* -- Metals & Alloys-- Corrosion & Erosion
ALLOYS
ALUMINIUM ALLOYS
ALUMINIUM COMPOUNDS
ALUMINIUM OXIDES
CHALCOGENIDES
CHEMICAL REACTIONS
INTERMETALLIC COMPOUNDS
MICROSTRUCTURE
NICKEL ALLOYS
NICKEL COMPOUNDS
NICKEL OXIDES
OXIDATION
OXIDES
OXYGEN COMPOUNDS
PHASE STUDIES
SCALING
TRANSITION ELEMENT COMPOUNDS