Tribological Properties of Magnet Structural Materials at Cryogenic Temperatures

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In this project tribological properties of magnet structural materials were investigated at cryogenic temperatures, because frictional heating due to sliding in a magnet caused the quench of it.(1)Frictional heatingIn the friction test at cryogenic temperature in liquid helium, temperature rise was measured by two thermocouples inserted into a specimen. Frictional heating appeared as a pulse with sharp fluctuation. Temperature rise was increased with frictional heat, but the relationship between them was not linear. This meant that not all the frictional heat generated but the some fraction of it contributed to the temperature rise of the specimen because of the cooling by liquid helium.Numerical simulation was carried out by using the experimental data of temperature rise. The simulation dealt with the inverse problem of unsteady heat conduction. From this simulation the temperature distribution of the specimen was obtained, where the temperature decreased steeply with depth from the … More interface of the specimen. Furthermore, the integrated heat flux showed the heat contributing to the temperature rise was less than 50 % of the frictional heat generated during sliding.(2)Friction test in vacuum at cryogenic temperatureA superconducting magnet is set in a vacuum vessel, and therefore, friction problem occurs in vacuum at cryogenic temperature. The experimental apparatus was constructed for the friction test in this environment, and friction tests were carried out for 24 combinations of specimen. In the cases such as JN2-JN2 the coefficient of friction was low at 5 K, but quite high at 77 K due to the adhesion between surfaces. On the other hand, in the case of JN2-CuNi the coefficient of friction was high at 4 K. These properties were dependent on hardness of materials. The hardness increased with decreasing temperature, and the adhesion was prevented above a certain value of the hardness. Temperature dependence of hardness was also obtained, where coefficient of friction increased between 20 to 50 K, and decreased between 80 to 110 K for JN2-Cu. Less