TRIBOLOGICAL PROPERTIES OF MAGNET STRUCTURAL MATERIALS AT CRYOGENIC TEMPERATURES IN VACUUM

在本课题中，研究了真空低温下磁体结构材料的摩擦学性能，因为磁体中的摩擦加热导致了磁体的失超，而摩擦阻力决定了结构部件在真空中的偏转。在真空低温摩擦试验中，考察了JN1-JN1、JN2-JN2、SUS316L-SUS316L、JN1-Cu4、JN2Cu3、JN2CuNi7种材料在4K~150K温度范围内的摩擦性能。摩擦性能有三种类型：(1)与温度无关，对于铜-铜、JN_2-CuNi和SU316L-SUS316L，摩擦系数在4.0左右；(2)对于JN1-JN1和JN_2-JN_2，随着温度的升高，摩擦系数逐渐增加；研究了真空室中残留气体的组成。20K时有H2气体，50K时有N_2气体，100K时有CO_2气体。金属硬度的变化将决定摩擦性能。真空温升对摩擦加热引起的温升进行了测量。然而，移动样品的温度没有冷却到足够的温度，导致测量不成功。冷却只是通过试件之间接触区域的热传导。今后应开发新的冷却移动试件的方法。Nb_3SN超导线材镀膜的评价为了减少交流损耗，通常在Nb_3SN超导线材上镀铬。然而，涂层被微小的滑动分离，出现了铜衬底。对不同涂层金属的线材在液氦中进行了摩擦试验和接触电阻测量。镀铬膜在前200次循环中破裂，表现为摩擦系数的增加和接触电阻的降低。经一定热处理后的非晶态钨合金薄膜表现出良好的性能。

In this project tribological properties of magnet structual materials were investigated at cryogenic temperatures in vacuum, because frictional heating in a magnet caused the quench of it, and frictional resistance determined the deflection of the structural components in vacuum.1. Frictional propertiesIn the friction test at cryogenic temperatures in vacuum, the temperature dependence of friction was examined from 4 K to 150 K for seven combinations of JN1-JN1, JN2-JN2, SUS316L-SUS316L, JN1-Cu, JN2-Cu, Cu-Cu and JN2-CuNi. There were three types of the frictional properties : (1) independent on temperature, where the friction was high at about 4.0 for Cu-Cu, JN2-CuNi, and SUSU316L-SUS316L, (2) gradual increase with temperature for JN1-JN1 and JN2-JN2, and (3) higher friction from 40 to 90 K for JN1-Cu and JN2-Cu. The composition of residual gases in a vacuum chamber was examined. H_2 gas at 20 K, N_2 gas at 50 K and CO_2 at 100 K appeared. The change in hardness of metals would determine the frictional properties.2. Temperature rise in vacuumTemperature rise due to frictional heating was tried to measure. However, the temperature of the moving specimen was not cooled enough, which resulted in the unsuccess of the measurement. The cooling was only the thermal conduction through the contact area between specimens. The new method to cool the moving specimen should be developed hereafter.3. Assessment of coated film in Nb_3Sn superconduction wireUsually Cr was plated on Nb_3Sn superconductiong wire to reduce AC loss. However, the coated film was separated by the small sliding, and Cu substrate appeared. The friction test and contacting resistance measurement were carried out in liquid helium for wires with different coating metals. Cr coated film was broken in the first 200 cycles, which was detected by the increase in coefficient of friction and the decrease in contacting resistance. Tungusten amorphous film with certain heat treatment showed the good performance.