Failure analysis of Sm2Co17 type permanent magnet for high temperature
With the increasing using temperature, the magnetic performance of high temperature stable Sm2Co17 type permanent magnet will be decreased. In order to explore the effect of the high temperature on microstructure of the alloy, the differential thermal analysis (DTA) was made and three distinct phase transformation temperature 254 °C, 342 °C and 540 °C were obtained. Then X-ray diffraction (XRD), scanning electron microscopy (SEM) and X-ray energy dispersive spectrometer equipped (EDS) were used to analyze the phase information, microstructure and composition of the samples treated at the above temperatures. The results suggested that the oxidation and precipitation of Cu and Fe are the key reason to result in the failure of the material, which provides an important reference for the research of the magnet.
Studies on corrosion conditions of metallographic sample of Sm_2Co_(17) permanent magnet materials
Sm2Co17 type permanent magnet materials were corroded under three kinds of corrosion conditions.Scanning electron microscopy and energy dispersive X-ray spectrometer were used to study the metallographic corrosion conditions.The result showed that sample corroded for 60 seconds in corrosive liquid of 100ml distilled water dissoled in 0.5ml nitric acid and 2ml acetic acid can clearly display boundary,surface of grain,and Zr-rich and Sm-rich phase in the grain.Compared with the corrosion agent most commonly used to metal material and the formula from metallographic corrosion handbook,the corrosion agent determined in this research can get a more clearly metallographic image.
Evaluation of Lapping Grains based on Shape Characteristics.
The shape and size of abrasive grains during lapping varies complicately and irregularly. In this study, the aspect ratio of grain size and the fractal dimension of the grain external form were used as shape characteristics of grain in order to evaluate grains with lapping time. The results obtained are summarized as follows : (1)The fractal dimension increases due to microscopic fracture and decreases due to macroscopic fracture or attritious wear. (2)The aspect ratio and the fractal dimension, which are grain shape characteristicsis of the macroscopic shape and the microscopic surface complication of grain respectively, can be used for evaluating grain shape variation during lapping.