TRIBOLOGICAL PROPERTIES OF MAGNET STRUCTURAL MATERIALS AT CRYOGENIC TEMPERATURES IN VACUUM

在这个项目中，研究了磁体结构材料在真空低温下的摩擦学性能，因为磁体中的摩擦加热会导致磁体的淬火，而摩擦阻力决定了真空中结构部件的挠度。在真空低温摩擦试验中，考察了JN1-JN1、JN2-JN2、SUS316L-SUS316L、JN1-Cu、JN2-Cu、Cu-Cu和JN2-CuNi 7种组合在4 ~ 150 K范围内的摩擦温度依赖性。有三种摩擦性能：(1)与温度无关，其中Cu-Cu、JN2-CuNi和SUSU316L-SUS316L的摩擦性能最高，约为4.0;(2)JN1-JN1和JN2-JN2随温度的升高而逐渐增加；(3)JN1-Cu和JN2-Cu的摩擦性能在40 ~ 90 K范围内较高。研究了真空室中残余气体的组成。20 K时出现H_2气体，50 K时出现N_2气体，100 K时出现CO_2气体。金属硬度的变化将决定其摩擦性能。真空中的温升尝试测量摩擦加热引起的温升。然而，由于运动试样的温度没有充分冷却，导致测量不成功。冷却只是通过试样之间的接触区域进行热传导。今后应发展新的运动试样冷却方法。Nb_3Sn超导导线镀层的评价通常在Nb_3Sn超导导线表面镀Cr以降低交流损耗。然而，涂层被小滑动分离，并出现Cu衬底。在液氦中对不同涂层金属丝进行了摩擦试验和接触电阻测量。镀铬膜在前200次循环中发生断裂，摩擦系数增大，接触阻力减小。经过一定热处理的钨非晶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.