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Title: Formation of Z-Ti{sub 50}Al{sub 30}O{sub 20} in the sub-oxide zones of {gamma}-TiAl-based alloys during oxidation at 1000 C

Abstract

The oxidation behavior of {gamma}-TiAl and {alpha}{sub 2}-Ti{sub 3}Al + {gamma}-TiAl alloys was studied at 1,000 C in pure oxygen up to 250 h. All alloy coupons were polished to a 1 {micro}m finish prior to oxidation. A series of {gamma}-Ti{sub 48}Al{sub 52} coupons polished to a 600-grit finish were also prepared. The type of scale which formed during oxidation and the consequent subsurface changes in the alloy were found to depend on the presence and amount of {alpha}{sub 2} in the starting alloy microstructure, surface finish, and oxidation time. The {gamma}-alloy with a 600-grit finish formed a protective Al{sub 2}O{sub 3}-rich scale during the early stages of oxidation, whereas the same alloy with a 1 {micro}m finish formed a less protective Al{sub 2}O{sub 3} + TiO{sub 2} scale. In the former case, a continuous subsurface layer of Z-Ti{sub 50}Al{sub 30}O{sub 20} formed from {gamma} by essentially equal amounts of oxygen enrichment and aluminum depletion; essentially no titanium diffusion was required. With continued oxidation, the continuous Z-layer destabilized at the Z/{gamma} interface into a mixture of {alpha}{sub 2}(O) + Z. The presence of {alpha}{sub 2}(O) + Z in the subsurface zone always corresponded to the growth of a non-protective Al{submore » 2}O{sub 3} + TiO{sub 2} scale, suggesting that {alpha}{sub 2}(O) precipitation initiates the breakdown of the initially formed Al{sub 2}O{sub 3}-rich scale. The subsurface zone in the {gamma} alloy with a 1 {micro}m finish varied, containing either internal Al{sub 2}O{sub 3} and no Z phase or {alpha}{sub 2}(O) + Z. The {alpha}{sub 2} + {gamma} alloys formed a non-protective Al{sub 2}O{sub 3} + TiO{sub 2} scale and subsurface zone of {alpha}{sub 2}(O) + Z at all the times studied. The discontinuous distribution of {gamma} in the two-phase alloys prevented formation of a continuous Z layer. The Z phase was determined to be metastable on the basis of equilibration experiments with Ti-Al-O alloys.« less

Authors:
;  [1];  [2]
  1. Univ. of New South Wales, Sydney , New South Wales (Australia). School of Materials Science and Engineering
  2. Univ. of New South Wales, Sydney, New South Wales (Australia). School of Materials Science and Engineering|[Iowa State Univ., Ames, IA (United States). Dept. of Materials Science
Publication Date:
OSTI Identifier:
684394
Resource Type:
Journal Article
Journal Name:
Acta Materialia
Additional Journal Information:
Journal Volume: 47; Journal Issue: 10; Other Information: PBD: 10 Aug 1999
Country of Publication:
United States
Language:
English
Subject:
36 MATERIALS SCIENCE; OXIDATION; TITANIUM ALLOYS; ALUMINIUM ALLOYS; INTERMETALLIC COMPOUNDS; TEMPERATURE RANGE 1000-4000 K; DIFFUSION; INTERFACES; PHASE TRANSFORMATIONS

Citation Formats

Copland, E.H., Young, D.J., and Gleeson, B. Formation of Z-Ti{sub 50}Al{sub 30}O{sub 20} in the sub-oxide zones of {gamma}-TiAl-based alloys during oxidation at 1000 C. United States: N. p., 1999. Web. doi:10.1016/S1359-6454(99)00169-X.
Copland, E.H., Young, D.J., & Gleeson, B. Formation of Z-Ti{sub 50}Al{sub 30}O{sub 20} in the sub-oxide zones of {gamma}-TiAl-based alloys during oxidation at 1000 C. United States. doi:10.1016/S1359-6454(99)00169-X.
Copland, E.H., Young, D.J., and Gleeson, B. Tue . "Formation of Z-Ti{sub 50}Al{sub 30}O{sub 20} in the sub-oxide zones of {gamma}-TiAl-based alloys during oxidation at 1000 C". United States. doi:10.1016/S1359-6454(99)00169-X.
@article{osti_684394,
title = {Formation of Z-Ti{sub 50}Al{sub 30}O{sub 20} in the sub-oxide zones of {gamma}-TiAl-based alloys during oxidation at 1000 C},
author = {Copland, E.H. and Young, D.J. and Gleeson, B.},
abstractNote = {The oxidation behavior of {gamma}-TiAl and {alpha}{sub 2}-Ti{sub 3}Al + {gamma}-TiAl alloys was studied at 1,000 C in pure oxygen up to 250 h. All alloy coupons were polished to a 1 {micro}m finish prior to oxidation. A series of {gamma}-Ti{sub 48}Al{sub 52} coupons polished to a 600-grit finish were also prepared. The type of scale which formed during oxidation and the consequent subsurface changes in the alloy were found to depend on the presence and amount of {alpha}{sub 2} in the starting alloy microstructure, surface finish, and oxidation time. The {gamma}-alloy with a 600-grit finish formed a protective Al{sub 2}O{sub 3}-rich scale during the early stages of oxidation, whereas the same alloy with a 1 {micro}m finish formed a less protective Al{sub 2}O{sub 3} + TiO{sub 2} scale. In the former case, a continuous subsurface layer of Z-Ti{sub 50}Al{sub 30}O{sub 20} formed from {gamma} by essentially equal amounts of oxygen enrichment and aluminum depletion; essentially no titanium diffusion was required. With continued oxidation, the continuous Z-layer destabilized at the Z/{gamma} interface into a mixture of {alpha}{sub 2}(O) + Z. The presence of {alpha}{sub 2}(O) + Z in the subsurface zone always corresponded to the growth of a non-protective Al{sub 2}O{sub 3} + TiO{sub 2} scale, suggesting that {alpha}{sub 2}(O) precipitation initiates the breakdown of the initially formed Al{sub 2}O{sub 3}-rich scale. The subsurface zone in the {gamma} alloy with a 1 {micro}m finish varied, containing either internal Al{sub 2}O{sub 3} and no Z phase or {alpha}{sub 2}(O) + Z. The {alpha}{sub 2} + {gamma} alloys formed a non-protective Al{sub 2}O{sub 3} + TiO{sub 2} scale and subsurface zone of {alpha}{sub 2}(O) + Z at all the times studied. The discontinuous distribution of {gamma} in the two-phase alloys prevented formation of a continuous Z layer. The Z phase was determined to be metastable on the basis of equilibration experiments with Ti-Al-O alloys.},
doi = {10.1016/S1359-6454(99)00169-X},
journal = {Acta Materialia},
number = 10,
volume = 47,
place = {United States},
year = {1999},
month = {8}
}