| With the development of morden industry, national defence, transportation and newly developing technology, the serving conditions of many equipments, apparatus and parts are more and more severe, and which raises the harsh terms to materials. The materials of high-termperature equipments not only need to content chemical properties, but also have a better oxidation resistance. Besides the atmosphere, the applied loading and other external environments also affect the oxidation resistance greatly. Therefore, the effect of applied loading and other external environments on the high-termperature oxidation is more and more paid attention to. By now, the tensile effect on the high-temperature oxidation or corrosion has been investigated extensively and detailedly, however, the effect of compressive stress on the high-temperature oxidation has been studied scarcely. As a state of external stress, compressive stress existes in many high-temperature parts, and the effect of which on the oxidation or corrosion behavior may affect the lifetime and security of serving materials. Thus, it is necessary to investigate the effect of compressive stress on the high-temperature oxidation behaviors. As an external environment, the effect of high magnetic field on the surface and interfacial diffusion behaviors has been investigated, but there has been no an accepted theory to be proposed. We studied the effect of magnetic field on the high-temperature oxidation behavior and the ions diffusion during the oxidation process, the purpose was to give more experimental results to further study the magnetic effect on the high-temperture oxidation and oxide-scale properties.In the present paper, some model alloys were used, such as pure Fe, Ni, and Fe-xCr, Ni-xCr, Fe-20Ni alloys. The oxide-scale microstructures and components were examined by optical microscopy (OM), scanning electronic microscopy (SEM), X-ray diffraction (XRD), and electronic probe microanalysis (EPMA) and so on. The oxidation kinetics oxidized under compressive stresses or magnetic field was estimated by thermogravimetric analysis (TGA) or thickness measurements. In addition, the stress relaxation of oxide scales and healing crack behavior were analyzed by examining the density or integrity of oxide scales. Moreover, high-temperature oxidation of three metallic materials under magnetic field was carried out. The major results as follows:(1) It was found that the oxidation rates were accelerated by the applied compressive stresses based on the analysis on the oxidation kinetics of metallic materials. The accelerated oxidation rates of pure Ni and Fe-20Cr alloy oxidized under compressive stress were related to the increased oxide nuclei. As the stress concentration and the induced aggregation of dislocations developed under compressive stress, the high energy zone would generate, at where oxide nucleation occurred. When the oxide nuclei increased, the grain boundaries in oxide scale also increased, and the actions and anions were easily diffuse along the grain boundaries, so the oxidation rate was accelerated. Besides, it was found that there was a compressive stress of about 5 MPa, at which the oxidation rate reached its maximum. This phenomenon was explained by analyzing the relation between the oxide size and the weight gain. As Fe-oxides formed on pure Fe, Fe-20Ni and Fe-16Cr alloy, the stress relaxation occurred in the form of oxide-scale cracks or spallation. It was due to that the Fe-oxides have lower Young's modulus and higher thermal expansion coefficient. The development of cracks or defects in the Fe-oxides applied the short-circuit paths for the oxygen transfer and cation diffusion, so the oxidation rates were accelerated. In addition, it was shown that the growth of intergranular and intargranular scale on Fe-20Ni alloy also accelerated owing to the development of cracks in the oxide scale(2) During the analysis on the stress relaxation in oxide scales, it was found that there was a critical compressive stress, above which the oxide scales would fail. The oxide scales on pure Ni and Fe-20Cr alloy showed plastic deformation to stress relief. For pure Ni, cavities developed at the NiO/Ni interface in the case of stressed condition, which weakened the interface. Thanks to the outward buckling and the smaller oxide size which can accommodate partial internal stress, the oxide scales of pure Ni are plastic deformed. In the case of Fe-20Cr, the formation of smaller oxide particles under compressive stress applied more grain boundaries in the scale. These grain boundaries played a role in the same effect on the stress relaxation. The slip bands were developed under 8 MPa compressive stress for 20 h of oxidation. Up to 65 h, however, plastic deformation in the form of grain boundary slide occurred when the applied stress was 4 MPa, and the healing cracks were observed. In the case of Ni-12Cr alloy, cracks existed after 72 h of oxidation for the unstressed samples. Wedge-type cracks formed on samples oxidized under 5 MPa compressive stress for 48 h. The formation of wedge-type crack was an evidence of healing cracks in an extent. Up to 72 h, obvious healing cracks were noticed, and it showed pseudoplasticity. For Fe-16Cr alloy, the oxide scales showed cracks and spallation because the oxide scale consisted of Fe-oxides, and multi-layer delamination was generated after 20 h of oxidation. Moreover, as the type of oxide has a remarkable effect on the stress relaxation, the precipitation of Fe3O4 from FeO under the mutual continuous cooling and compressive stress conditions was studied, the results showed that the applied compressive stresses accelerated the precipitation of Fe3O4 from FeO.(3) The high-temperature oxidation behaviors of pure Fe, Fe-20Ni and Fe-5Cr alloys oxidized under high magnetic field were investigated. It was found that the application of parallel high magnetic field induced an increase in the oxidation rate of pure Fe, and induced the occurrence of oriented growth of FeO layer. But the effect of perpendicular magnetic field on the growth of oxide scale was not pronounced. In the case of Fe-20Ni alloy, the application of parallel high magnetic field retarded the growth of oxide scales, and the oriented growth of subscale was induced. Besides, the growth of scale and Cr-riched layer on Fe-5Cr alloy was suppressed by the application of parallel magnetic field.
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