Microscopic Analysis Of SmCo Magnets And The Effect Of Its Magnetic Field On The Imaging Of SEM

Since the 2:17 SmCo alloys were developed and researched in the 1970 s,its high magnetic properties,lighter weight,and smaller volume are in line with the rapid development of the aerospace industry in China for devices requirements of miniaturization and integration.At the same time,due to the high Curie temperature of SmCo permanent magnets and its high temperature stability,this also makes them the best candidates for permanent magnet materials and devices operating in high temperature environments.However,when it is used for a long period of time under a high temperature environment,an oxide layer is formed on the surface,resulting in a decrease in the performance of the magnet and the device and resulting in failure.Therefore,it is necessary to study the micro-failure analysis and analysis methods of magnetic materials such as SmCo permanent magnets.At the same time,non-demagnetized magnetic samples will affect the scanning electron microscope(SEM).In this paper,the aging mechanism of SmCo permanent magnetic materials under long-term high-temperature aerobic conditions and the influence of its magnetic field on the SEM analysis process are analyzed.The main work of this paper is as follows:(1)Significant reduction in the quality of the SEM image caused by the magnetic field of the magnetic sample,mainly due to the deflection of the electron trajectories by the Lorentz force.In this paper,a rectangular SmCo permanent magnet sample with incomplete demagnetization is used as a magnetic field source,and samples are placed in different magnetic field directions for experimentation.Combining related theories and COMSOL software,the effect of magnetic field direction on SEM secondary electron imaging is analyzed,and the best observation is given.Direction and discuss its principles.(2)A magnetic field using a regular magnet was studied so that an SEM not equipped with a backscattered electron detector can obtain a method with an image of composition contrast similar to a backscattered image in a secondary electron mode.In this paper,the non-demagnetized SmCo permanent magnet sample was used as the magnetic field source.The surface-etched copper foil was photographed by SEM.Finally,the obvious contrast of the component was obtained in the secondary electron mode,and the theoretical analysis and COMSOL were also performed.Simulations discuss the causes of compositional contrast.(3)The SEM,EDS and XRD microscopic analysis methods were used to analyze the composition,morphology and forming speed of the surface oxide layer of Ni-coated SmCo permanent magnets at 550 °C in air for a long period of time ranging from 0 to 5000 h.It is found that the long-term aging of the surface oxide layer is mainly composed of oxides of Cu,Co,and Fe,and the formation sequence and mechanism of different oxides are discussed.At the same time,the speed of the thickening of the oxide layer is shown to be faster and slower,which is consistent with Wanger’s formula.The main reason is that the thickening of the oxide layer itself blocks the oxygen.