EDP Sciences Journals List
Issue J. Phys. IV France
Volume 03, Number C9, Décembre 1993
Proceedings of the 3rd International Symposium on High Temperature Corrosion and Protection of Materials
Actes du 3ème Colloque International sur la Corrosion et la Protection des Matériaux à Haute Température
Page(s) C9-403 - C9-410
DOI http://dx.doi.org/10.1051/jp4:1993942

Proceedings of the 3rd International Symposium on High Temperature Corrosion and Protection of Materials
Actes du 3ème Colloque International sur la Corrosion et la Protection des Matériaux à Haute Température

J. Phys. IV France 03 (1993) C9-403-C9-410

DOI: 10.1051/jp4:1993942

Oxidation resistance of TiAl improved by a CoCrAl coating

Shigeji Taniguchi1, Toshio Shibata1, Naoyuki Asanuma2, Hanyi Luo3, Fuhui Wang3 and Weitao Wu3

1  Faculty of Engineering, Osaka University, 2-1 Yamadaoka, Suita, Osaka 565, Japan
2  Graduate School of Engineering, Osaka University, Japan
3  Institute of Corrosion and Protection of Metals, The Chinese Academy of Sciences, Wencui Road 62, 110015 Shenyang, China


Abstract
The oxidation behavior of TiAl coupons coated with a fine-grained Co-30Cr-4Al (mass %) layer of about 30 µm thickness was studied at 1100-1400 K in a flow of purified oxygen at atmospheric pressure for up to 500 ks. Three oxidation stages were recognized: initial transient, parabolic, and acceleration stages. However, at 1100 K a parabolic stage continues for more than 800 ks. The parabolic rate constants agree well with the reported values for alumina-former alloys. Voids are developed mainly at the scale/coating and coating/substrate interfaces as the oxidation proceeds. This is attributable to a slightly loose structure of the coating, its recrystallization during oxidation, and a Kirkendall effect due to preferential diffusion of Co into the substrate. The accelerated oxidation can be explained in terms of the formation of microcracks in convoluted scales. At 1400 K the growth of rutile on the scale seems to be additionally contributing to the acceleration.



© EDP Sciences 1993