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Author Schumann, E. ♦ Ruehle, M.
Source United States Department of Energy Office of Scientific and Technical Information
Content type Text
Language English
Subject Keyword MATERIALS SCIENCE ♦ ALUMINIUM ALLOYS ♦ OXIDATION ♦ NICKEL ALLOYS ♦ ALUMINIUM OXIDES ♦ INTERMETALLIC COMPOUNDS ♦ MICROSTRUCTURE ♦ NICKEL OXIDES ♦ PHASE STUDIES ♦ SCALING ♦ ALLOYS ♦ ALUMINIUM COMPOUNDS ♦ CHALCOGENIDES ♦ CHEMICAL REACTIONS ♦ NICKEL COMPOUNDS ♦ OXIDES ♦ OXYGEN COMPOUNDS ♦ TRANSITION ELEMENT COMPOUNDS ♦ Metals & Alloys- Corrosion & Erosion
Abstract 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].
ISSN 09567151
Educational Use Research
Learning Resource Type Article
Publisher Date 1994-04-01
Publisher Place United States
Journal Acta Metallurgica et Materialia
Volume Number 42
Issue Number 4


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