机械合金化铁硅钇合金的高温氧化行为

High-temperature Oxidation Behavior of Mechanical Alloying FeSiY Alloys

通过金相显微镜、热重分析、X射线衍射仪及带有能谱的扫描电子显微镜等研究了添加Y和机械合金化(MA)对Fe Si合金在900℃、0.1 MPa纯氧气条件下高温氧化行为的影响。结果表明,与熔炼(CC)Fe-3Si合金相比,MA Fe-3Si-0.5Y和MA Fe-3Si-5.0Y合金的晶粒尺寸明显降低,但在24 h氧化过程中,MA合金的氧化增重明显增加,这归因于晶粒细化提高了合金中的晶界密度,增加了合金各组元和氧的传质速率,促进了氧化过程的进行。与MA Fe-3Si-0.5Y相比,MA Fe-3Si-5.0Y合金在氧化初期表现出较高的氧化速率和较大的氧化增重,但3 h后合金的氧化速率迅速降低,这归因于氧化膜内层钇氧化物的迅速生成和富集。钇的添加减少了'Kirkendall空位'和阳离子空位所形成的孔洞,抑制了合金基体和氧化膜界面空腔和裂纹的形成,提高了合金氧化膜的粘附性。

By means of optical microscope(OM),thermogravimetric analysis(TGA),X-ray diffraction(XRD) and scanning electron microscope(SEM) equipped with an energy-dispersive X-ray spectrometer attachment(EDX),the effect of the rare-earth yttrium addition and mechanical alloying(MA) on the high-temperature oxidation behavior of Fe Si alloys was studied at 900 ℃ in 0. 1 MPa flowing pure O2. Results show that,compared to the conventional casting(CC) Fe-3 Si alloy,the grain size of MA Fe-3 Si-0. 5 Y and MA Fe-3 Si-5. 0 Y alloys is remarkably decreased,but during the 24-h oxidation,the mass gain of the MA alloys increases obviously,which is due to the fact that grain refinement enhances the density of grain boundaries,promotes the diffusion of the alloying elements and oxygen,and thus accelerates the oxidation process. Compared to MA Fe-3 Si-0. 5 Y alloy,MA Fe-3 Si-5. 0 Y alloy exhibits relatively larger initial oxidation rate and mass gain,but after 3-h oxidation,the oxidation rate is reduced much,which is due to the rapid formation and enrichment of yttrium oxides in the inner oxide scale. The addition of yttrium decreases the number of the Kirkendall vacancies and the holes originated from the cation vacancies,which inhibits the cavity and crack formation at the interfaces between the substrate and oxide film,and improves the adhesion of the oxide scales.