Premium
The Oxidation of cobalt‐tantalum base alloys containing carbon
Author(s) -
ElDahshan M. E.,
Hazzaa M. I.
Publication year - 1987
Publication title -
materials and corrosion
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.487
H-Index - 55
eISSN - 1521-4176
pISSN - 0947-5117
DOI - 10.1002/maco.19870380805
Subject(s) - tantalum , cobalt , materials science , carbide , carbon fibers , oxide , tantalum carbide , alloy , cobalt oxide , inorganic chemistry , metallurgy , chemistry , composite material , composite number
The oxidation of cobalt‐tantalum carbon alloys, containing 10 and 15 wt.% Ta and carbon in the range 0–1 wt%, was carried out in oxygen and air at atmospheric pressure at 900, 1000 and 1100°C. The alloys oxidised according to the parabolic rate law with activation energy of about 38 Kcal/mole. In general, the addition of tantalum decreases the oxidation rates, in comparison with cobalt and with the same mass of chromium added to cobalt. Again, the presence of carbon in the Co‐Ta alloys decreases its oxidation rates in comparison with carbon‐free alloys. The scales formed on Co‐Ta and Co‐Ta‐C alloys consist mainly of an outer layer of cobalt oxide, CoO, and an inner porous layer of mixture of oxides: cobalt oxide; CoO, tantalum oxide; Ta 2 O 5 , and solid solution of these two oxides; CoTaO 4 at all temperatures in the range of 900°‐1100°C. The binary Co −10% Ta and Co −15% Ta show an internal oxidation along the internal phase, increasing of alloy tantalum content increases the density of the internal phase. The presence of carbon in the ternary Co‐Ta‐C alloys has little effect and there is no apparent preferential penetration along the tantalum carbide network. In contrast to carbide present in Co‐Cr‐C alloys, where these carbides were preferentially attacked, the outer scale was disrupted, due to the formation of carbon gaseous oxides.