Ce对Fe-Cr合金高温氧化行为的影响

Fe-15Cr 和 Fe-30Cr 合金在1000至1200℃空气中氧化时,表面富铁氧化伤的发展导致保护性Cr_2O_3层衰退,氧化速率增大。添加 Ce 可延迟衰退过程的发生,从而大幅度减低氧化速率。随氧化温度和合金成份变化,Cr_2O_3层衰退的开始时间和发展特征随之改变,Ce 对氧化行为的影响因而呈现出规律性的变化。研究发现,合金中 Cr 的内氧化使 Cr_2O_3层形成小舌包卷合金并使其氧化成富铁氧化物。这是Cr_2O_3层衰退的原因之一。含 Ce 合金中 Ce 的优先内氧化则降低自氧化层进入合金的氧浓度,抑制Cr 的内氧化。氧浓度降低还能促进 Si 的内氧化物在氧化层/合金界面集聚。

THE EFFECT OF Ce ADDITION ON HIGH TEMPERATURE OXIDATION OF Fe-Cr ALLOYS

The influence of 0.15 or 0.70wt% Ce addition on the oxidation of Fe-15Cr and Fe-30Cr alloys in air at the temperature range between 800 and 1300℃ up to 500hr was studied.The oxidation kinetics indicated that the oxidation rates of Fe-15Cr alloy at 1000℃ and 1100℃ and that of Fe-30Cr alloy at the tem peratures from 1000 to 1200℃ reduced remarkablely owing to the 0.7wt%Ce added.However,the effect of 0.15wt%Ce was much less. The morphology observation,X-ray diffraction analyses and EPMA were carried out for the oxide layers on test alloys.The studies showed that Cr_2O_3 films could be formed rapidly on the surfaces of all test alloys at an early stage of oxidation,and then the Fe-ion concentration in Cr_2O_3 remained somewhere about 1wt% for a long time.However,the 0.7wt%Ce addition decreased the growth rate of Cr_2O_3 layer slightly.The most obvious effect of Ce was to inhibit Cr_2O_3 layer degeneracy in which Cr_2O_3 was replaced gra- dually by rapidly growing Fe-rich oxide,and to delay the breakaway of oxide film. The concentration of oxygen diffused into alloy from Cr_2O_3 layer is reduced by a factor of 10~7 owing to internal oxidation of Ce.With the reduction of oxygen concentration in alloy,internal oxidation of Si in Fe-15Cr alloys which contained about 0.2wt%Si took place in the vicinity of the Cr_2O_3 layer/alloy interface,so that a SiO_2 interface layer was formed in the Fe-15Cr-0.7Ce alloy.