A parametric study of low friction coating by PVD method on the spiralock female thread for ITER application

Abstract

The hard lubrication is defined that the thin films are deposited by radio-frequency magnetron sputtering from the target material on substrate in order to improve their desired properties such as hardness, friction and wear resistance. Especially, the MoS2 coating can be used in high vacuum and aerospace environments for lubrication purposes, which low friction is required. Unlike fluid lubrications, MoS2 is suitable for use in a vacuum environment because it has low outgassing pressure and lack of migration. For this reason, the sputtered MoS2 coating is primarily considered as low friction / anti-seize coating method of the ITER blanket central bolt insert. A magnetron sputtering process, which permits friction coefficient and durability of the MoS2 coating, suites to coat precision mechanical component with its exquisitely thin thickness. However, the coating on the spiralock female thread of blanket central bolt inserts is difficult to have uniform coating deposition due to its shadow effect. Therefore, it is necessary for understanding the parameters and effects of sputtering process to achieve the uniform coating having the required friction coefficient less than 0.05. Details of parametric study with various sputtering conditions on the simple disk and spiralock female thread to reach required friction coefficient and uniform coating thickness, are presented in this paper.