Kinetic and Microstructural Analyses of Chromia Forming Alloys during Cyclic Oxidation  

作　　者：N.K.OTHMAN D.J.YOUNG 

机构地区：[1]School of Materials Science & Engineering,University of New South Wales,Sydney 2052 Australia

出　　处：《中国腐蚀与防护学报》2009年第4期315-315,共1页Journal of Chinese Society For Corrosion and Protection

摘　　要：Three Fe-Cr model alloys(Cr:9,17,and 25 wt%) were subjected to cyclic oxidation in Ar-10%H_2-5%H_2O(p_(o_2)=3.6×10^(-22) atm),Ar-20%O_2 and Ar-20%O_2-5%H_2O atmospheres at 700℃.In general,increasing alloy chromium levels reduced the oxidation rate.At high p_(o_2),in the absence of water vapour,the 9%Cr alloy exhibited breakaway oxidation at the beginning of the reaction.However, for chromium levels≥17%,no breakaway oxidation occurred,and the weight gain was very low.Adding water vapour to Ar-20%O_2 accelerated the oxidation of alloys containing 17%Cr or less.However,this accelerating effect was not evident for high chromium alloys.At low p_(o_2),breakaway oxidation of alloys with chromium concentration≤17%occurred after 300 cycles exposure.High chromium content alloys did not undergo significant oxidation.XRD analysis showed that for low chromium content alloys(Cr≤17%), spinel and wustite were formed in the low p_(o_2) gas,while in the high p_(o_2) gas,hematite,magnetite and spinel were produced.In the case of high chromium alloys,only Cr_2O_3 was detected.Metallographic examination showed that the spinel was present in the form of internal precipitates.A dense chromia layer was observed at alloy chromium levels above 25%.The reasons for the difference in oxidation behaviour at different oxygen potentials,and the effect of water vapour are discussed in connection with the microstructure of the oxides.Three Fe-Cr model alloys （Cr： 9, 17, and 25 wt%） were subjected to cyclic oxidation in Ar-10%H2-5%H2O （po2=3.6×10^-22 atm）, Ar-20%O2 and Ar-20%O2-5%H2O atmospheres at 700 ℃. In general, increasing alloy chromium levels reduced the oxidation rate. At high Po2, in the absence of water vapour, the 9%Cr alloy exhibited breakaway oxidation at the beginning of the reaction. However, for chromium levels≥17%, no breakaway oxidation occurred, and the weight gain was very low. Adding water vapour to Ar-20%O2 accelerated the oxidation of alloys containing 17% Cr or less. However, this accelerating effect was not evident for high chromium alloys. At low Po2, breakaway oxidation of alloys with chromium concentrationS17% occurred after 300 cycles exposure. High chromium content alloys did not undergo significant oxidation. XRD analysis showed that for low chromium content alloys （Cr≤17%）, spinel and wustite were formed in the low Po2 gas, while in the high po2 gas, hematite, magnetite and spinel were produced. In the case of high chromium alloys, only Cr2O3 was detected. Metallographic examination showed that the spinel was present in the form of internal precipitates. A dense chromia layer was observed at alloy chromium levels above 25%. The reasons for the difference in oxidation behaviour at different oxygen potentials, and the effect of water vapour are discussed in connection with the microstructure of the oxides.

关 键 词：镁合金 氧化 腐蚀 防护 

分 类 号：TG17[金属学及工艺—金属表面处理]