Effect of dispersed oxides of rare earths and other reactive elements on the high temperature oxidation resistance of Fe
- PDF / 2,964,100 Bytes
- 8 Pages / 594 x 774 pts Page_size
- 75 Downloads / 241 Views
THE effect of finely distributed
with the addition of 0.3 wt pct glycerin as the lubricant and compacted at a pressure of 2 • 106 g / c m z to 10 • 10 x 100 m m compacts and pre-heated in vacuum at 573 K for 2 h to remove the lubricant. The compacts, sealed in quartz capsules, were sintered at 1473 K for about 170 h. The sintered alloys were hot-rolled to one m m thick sheets at 873 K and cut into 10 • 10 • 1 m m size sample. The specimens were abraded with silicon carbide paper, degreased and annealed in vaccum at 1373 K for 48 h to relieve stress and to minimize grain growth during the subsequent oxidation process. In order to clarify the effect of using sintered materials, Fe-20Cr-1 pct Cr203 and Fe-20Cr alloys were prepared by the same procedure described above and in addition a Fe-20Cr alloy was also prepared by arc-melting. An example of the dispersoid distribution in Fe20Cr-1 pct Y203 after annealing rolled sheet for 48 h at 1273 K is shown in Fig. 1. This structure is quite similar to those found in other alloys with and without dispersoids. The dispersoid distribution in the alloys was uniform. It should be noted that Cr20 3 was also present as a dispersed oxide in all the alloys. It was EXPERIMENTAL formed from oxygen present in the original powder The starting materials were -100 mesh size iron materials. The specimens were isothermally oxidized in 1 atm powder, -325 mesh chromium powder and powders of the reactive metal oxides ranging from 0.1 to 0.01 ~ m air at 1273, 1323 and 1373 K. N o attempt was made to diam. Fe-20Cr-1 wt pct MOv materials were prepared control the water content of the oxidizing atmosphere. by conventional powder metallurgical procedure, where The dew point of the air was approximately 276 K the powders were well mixed at the desired composition based on the typical humidity in the laboratory. Oxidation kinetics were determined by weight gain measHIROSHI NAGAI, YOSHIKI TAKEBAYASHI and HIROurements. The specimen was placed in an alumina pan YASU MITANI are Associate Professor, Graduate Student and suspended by a platinum wire in a quartz tube. A Emeritus Professor, respectively,Department of Materials Science resistance wound furnace was raised to surround the and Engineering, Osaka University, Yamada-kami, Suita, Osaka 565, Japan. tube so that the specimen was exposed in a uniform hot Manuscript submitted June 8, 1979. zone at the desired temperature. Although the weight ISSN 0360-2133/81/0311-0435500.75/0 METALLURGICAL TRANSACTIONSA 9 1981 AMERICAN SOCIETY FOR METALS AND VOLUME12A, MARCH 1981--435 THE METALLURGICAL SOCIETY OF AIME
stable oxides such as ThO2, CeO 2, Y203 or other rare earth metal oxides on the high temperature oxidation behavior of alloys based on Ni-Cr, Co-Cr or Fe-Cr have been well documented. HI Similar dispersions in pure Cr were also shown to modify the oxidation rate. 12,13 Although a n u m b e r of models have been proposed to explain the mechanism by which the dispersed oxides modify the oxidation behavior of these alloys, the mechanism has not been clear
Data Loading...
