【作者】 孙玥；

【导师】 曹中秋；

【作者基本信息】 沈阳师范大学 ， 应用化学， 2011， 硕士

【摘要】 高温合金的化学稳定性得益于其表面能否形成连续致密、附着性良好的氧化膜。用传统的电弧熔炼法制备的常规尺寸三元复相合金由于受到组元间固溶度的限制,无法避免其显微组织的不均匀,这使得合金表面形成活泼组元选择性外氧化膜所需的临界浓度较高。为降低活泼组元的临界浓度,采用机械合金化并通过热压使合金显微组织细化是较好的办法之一。本文采用机械合金化方法,通过热压制备了纳米晶Fe-Ni-Cr和Fe-Cr-Al合金,研究了它们在700-900℃、0.1MPa纯氧中的氧化行为,比较了纳米晶合金与相同组分的常规尺寸合金氧化行为的差异,探讨了晶粒细化对其氧化行为的影响。PMFe-40Ni-20/15Cr和MAFe-40Ni-20/15Cr合金的氧化动力学曲线均偏离抛物线规律。在高温氧化过程中,相同的温度下,MAFe-40Ni-20/15Cr合金的氧化速率明显小于PMFe-40Ni-20/15Cr合金。PMFe-40Ni-20/15Cr合金表面没有形成保护性的Cr2O3膜,而MAFe-40Ni-20/15Cr合金表面则形成了保护性的Cr2O3膜。在相同温度下,PMFe-40Ni-20Cr合金的氧化速率大于PMFe-40Ni-15Cr合金,MAFe-40Ni-20Cr合金的氧化速率小于MAFe-40Ni-15Cr合金。PMFe-60Ni-15Cr和MAFe-60Ni-15Cr合金的氧化动力学曲线均偏离抛物线规律。相同温度下,MAFe-60Ni-15Cr合金的氧化速率明显小于PMFe-60Ni-15Cr合金。在高温氧化过程中,PMFe-60Ni-15Cr合金表面没有形成保护性的Cr2O3膜,而MAFe-60Ni-15Cr合金表面则形成了保护性的Cr203膜。PMFe-10Cr-2.5Al和MAFe-10Cr-2.5Al合金的氧化动力学曲线均偏离抛物线规律。相同的温度下,MAFe-10Cr-2.5Al合金的氧化速率明显小于PMFe-10Cr-2.5Al合金。在高温氧化过程中,PMFe-10Cr-2.5Al合金表面没有形成保护性的Cr2O3膜,而MAFe-10Cr-2.5Al合金表面则形成了保护性的Cr2O3膜。机械合金化使合金晶粒尺寸降低,产生大量晶界,同时增大了组元的有效扩散系数,导致合金中的活泼组元以更快的速度向外扩散,降低了合金表面形成活泼组元选择性外氧化膜所需的临界浓度,有助于在高温氧化过程中形成保护性的外氧化物膜。更多还原

【Abstract】 Chemical stabilities of high-temperature alloys depend on the continuous, good adhesion and slow growth oxide scales formed on the alloy surface in high temperature oxidation processes. Ternary multiphase alloys of coarse-grained prepared by conventional arc-melting can not avoid from the microstructure with bigger grain size and the non-uniformity of phase distribution, which requires a higher critical concentration of the reactive component to form selective external oxidation. To decrease the critical concentration needed to form selective external oxide scales, microstructure refinement by mechanical alloying and hot pressing is one of the better ways. In this paper, the nanocrystalline Fe-Ni-Cr and Fe-Cr-Al alloys were prepared by mechanical alloying and afterwards hot pressing, while corresponding coarse-grained alloys were prepared by powders metallurgy. Moreover, the oxidation behavior of these alloys at 700-900℃under 0.1MPa oxygen pressures and the effect of grain size on their oxidation behavior were also studied as compared with the corresponding coarse-grained alloys.The oxidation kinetics of PMFe-40Ni-20/15Cr, and MAFe-40Ni-20/15Cr alloys all deviate from the parabolic law. At the same temperature, the oxidation rates of PMFe-40Ni-20/15Cr are higher than those of MAFe-40Ni-20/15Cr alloy. In the high temperature oxidation process, protective Cr2O3 scales are unable to form on the surface of PMFe-40Ni-20/15Cr alloy but form on the surface of MAFe-40Ni-20/15Cr alloy. At the same temperature, the oxidation rate of PMFe-40Ni-20Cr alloy is higher than that of PMFe-40Ni-15Cr alloy,and the oxidation rate of MAFe-40Ni-20Cr alloy is lower than that of MAFe-40Ni-15Cr alloy.The oxidation kinetics of PMFe-60Ni-15Cr and MAFe-60Ni-15Cr alloys all deviate from the parabolic law. The oxidation rates of MAFe-60Ni-15Cr alloy is lower than those of PMFe-60Ni-15Cr alloy at the same temperature. In the high temperature oxidation process, protective Cr2O3 scales are unable to form on the surface of PMFe-60Ni-15Cr alloy but formed on the surface of MAFe-60Ni-15Cr alloy.The oxidation kinetics of PMFe-10Cr-2.5Al alloy and MAFe-10Cr-2.5Al alloys all deviate from the parabolic law. The oxidation rates of MA Fe-10Cr-2.5Al alloy are significantly smaller than those of PMFe-10Cr-2.5Al alloy at the same temperature. In high temperature oxidation process, protective Cr2O3 scales are unable to form on the surface of PMFe-10Cr-2.5Al alloy but formed on the surface of MA Fe-10Cr-2.5Al alloy.Mechanical alloying decreases the grain size and produces a large number of grain boundaries, and increases effective diffusion coefficients of components. Thus, the reactive components in the alloy are able to diffuse outward faster, which are benefit to decrease the critical concentrations needed to form Cr oxide Cr2O3 scales and form the continuous scales of Cr2O3 scales as compared with the corresponding coarse-grained alloys alloy under the same conditions.更多还原