Justification for the Selection of Low Friction/Anti-seize Coatings in Applying Bolted Joints of Fusion Experimental Reactors

The article is dedicated to the relevant task for providing antifriction/anti-seize properties via a solid lubricant coating of highly loaded bolted joints of fusion experimental reactors such as ITER (International Thermonuclear Experimental Reactor), JET (Joint European Torus), JT-60SA (International Fusion School). The high-strength bolted joints with a self-locking Spiralock® technology are subjected to various negative factors (vibration, impact loads, thermal cyclic heating, degradation of properties, swelling and etc.) under radiation in high vacuum. Design equations are formulated for estimating coefficient of friction in the thread and on the bearing surface during the tightening/untightening procedure for bolted joints with the Spiralock® technology. The derived equations may be used as a part of analytical engineering method for assessing a design adequacy of low friction/anti-seize coating via obtained the working ranges of friction coefficient in threaded pairs. Applying to the fusion machines bolted joints, there were obtained the some tribological results concerning the friction behavior of the Alloy 718 ─ 100Cr6, SS660 ─ 100Cr6 pairs by performing the ball-on-disk sliding tests through rotation in the presence of a solid lubricant Rocol® based on molybdenum disulfide. The results of tribological tests in air under normal load \(N\)  = 5–25 N at a sliding speed \(v\)  = 5 · 10–4 m/s showed that the lubricant performed well, providing a low coefficient of friction of \(\mu\)  = 0.06–0.22. The values of friction coefficients in air that we obtained should be compared with additional friction and wear tests in a vacuum for the selected low friction/anti-seize coating with dry lubricating abilities based on MoS2 or graphite.