Stability of alpha phase in alumina-chromia plasma sprayed deposits after annealing
- Inst. of Plasma Physics, Prague (Czech Republic)
In plasma sprayed Al{sub 2}O{sub 3} deposits usually a spinel structure forms which lacks some of the desirable properties. In order to obtain the hard and stable {alpha}-Al{sub 2}O{sub 3} phase in coatings, additions of some other metal oxides are considered. Chromia (Cr{sub 2}O{sub 3}) studied in this paper has been chosen because of its complete solid solubility in Al{sub 2}O{sub 3} and because of its crystal lattice type which is close to that of Al{sub 2}O{sub 3}. Several feedstock powders with 0 to 37 wt% of chromia, prepared by various technologies, were used for spraying in air by the water stabilized plasma gun PAL 160. Comparison of feedstock powders, free-flight particles and deposits proved that the dwell time above the melting temperature during spraying is sufficiently long for mutual dissolution of both components and formation of one solid solution (Al, Cr){sub 2}O{sub 3}. This time was, however, short for reaching a large scale chemical homogeneity as it was confirmed by the X-ray chemical microanalysis and by asymmetry of XRD line profiles of the alpha phase. The as-sprayed materials were then annealed at temperatures up to 1,300 C and their phase composition was checked. Amount of the mixed {alpha}-(Al, Cr){sub 2}O{sub 3} changed with temperature of annealing. At lower temperatures and shorter holding times amount of {alpha}-phase decreases while metastable {theta}-phase appears and fraction of {gamma}-phase increases. At temperatures above 1,100 C amount of {alpha}-phase again increases similarly to the bulk ceramics.
- OSTI ID:
- 160534
- Report Number(s):
- CONF-940684-; ISBN 0-87170-509-5; TRN: IM9603%%116
- Resource Relation:
- Conference: 1994 national thermal spray conference, Boston, MA (United States), 20-24 Jun 1994; Other Information: PBD: 1994; Related Information: Is Part Of 1994 Thermal spray industrial applications: Proceedings; Berndt, C.C.; Sampath, S. [eds.] [State Univ. of New York at Stony Brook, NY (United States). Dept. of Materials Science and Engineering]; PB: 816 p.
- Country of Publication:
- United States
- Language:
- English
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