Effect of Ring Hardness on Friction and Wear Properties of Gold-Base Alloy Slip Rings

Gold-based alloy is one of the typical sliding electrical contact materials, with the advantages of better chemical stability, electrical and thermal conductivity and low contact resistance, and it is widely used in military industry and aerospace fields, such as solar panel drive mechanism, control moment gyroscope, antenna pointing mechanism and so on. With the rapid development of a new generation of military satellites, the demands for satellites with long life and high reliability indexes are increasing, which require higher requirements for the contact stability and wear resistance of aerospace electrical contact materials. Hardness is one of the important properties of materials. Improving the material hardness and reasonably matching the hardness value of friction pairs have a very important impact on tribological properties. The existed research results show that the addition of alloying elements, ion implantation or heat treatment can significantly improve the hardness, wear resistance and friction reduction of materials. However, there are few reports referred to the affect of materials hardness of gold-based alloy slip rings on tribological properties, especially the influence of ring hardness. In order to clarify the influence of ring hardness on its service life and optimize the selection of the frictional material, the tribological properties of AuAgCu alloy rings and AuNi alloy brushes were studied at room temperature in the atmosphere in this paper. Firstly, the microstructures of two different hardness rings were observed by the metallographic microscope. The results indicated that the grain size of the hard ring was smaller, which was mainly due to the different rolling and heat treatment processes. The deformation of the hard ring increased during the rolling process, and a certain degree of recrystallization occurred in the work-hardening structure during heat treatment. The nanoindentation test also confirmed that with the increase of ring rolling deformation, the degree of lattice distortion could increase, and the hardness and elastic modulus of the material could also increase. Then, the friction and wear test results showed that as the hardness of the ring increased from 200.4 HV to 243.6 HV, the average friction coefficient significantly decreased from 0.019 to around 0.04, and the width of ring wear marks decreased, which was related to many factors such as material microstructure and properties, friction pair hardness matching and the surface state. The life test of rings with different hardness was conducted using a dedicated running in equipment, and the results showed that the contact areas of the ring and the brush wire had typical adhesive wear morphology, and the wear areas of the brush wire wer irregular. However, the obvious ploughing scratch morphology was obtained in the wear area of the hard ring. The wear debris produced by conductive slip rings with different ring hardness were flaky and had no agglomeration, and the composition of wear debris was consistent with that of ring metal material. In addition, through the mass analysis of rings and brushes before and after life test, it was known that the wear quality of the ring significantly decreased from 0.0051 g to 0.003 g with the increase of the ring hardness. Reasonable matching of the hardness of friction pairs was very important for the slip ring to reduce wear. Therefore, better anti-friction and anti-wear effects could be obtained by increasing the ring hardness of gold-base alloy slip rings in a certain range, which provided the experimental and theoretical basis for the compatibility of electrical contact materials.