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Fretting wear is one of the main factors restricting the fastener service reliability for the high-temperature titanium alloys. Enhancing the high-temperature fretting wear resistance of titanium alloys with laser cladding coatings is an effective method. Thus, in this work, a self-lubricating composite coating was designed and fabricated on the surface of TC21 titanium alloy with laser cladding. Special attentions were made to the effect of the fractions of the hard and self-lubricating phases on high-temperature fretting resistance. In addition, the contribution of laser cladding power was also concerned. The primary phases of the self-lubricating composite coatings are α-Co, CaF 2 , WC, TiC and Cr 23 C 6 , and the reasons for the formation of TiC and Cr 23 C 6 are investigated from a thermodynamic point. The prepared composite coatings are dense and uniform. The crystallographic characteristics and the volume fractions of the hard phases (WC, TiC and Cr 23 C 6) and self-lubricating phase (CaF 2) were revealed, and the effect of grain size on the coating properties was analyzed. The hardness of the coatings were all maintained around 700 HV 0.2 , which was significantly higher than that of the substrate. The composite coating significantly improves the friction and wear resistance at 500 ℃. The hard phase was also found to be the most resistant to friction and wear. The frictional performance of the coating gets better when the hard phase and the self-lubricating phase increase. However, the hard phase contributes more to the high-temperature friction and wear resistance than the self-lubricating phase and the wear volume is 1/40 that of substrate. For the laser cladding power, the higher power can lead to a higher fraction of CaF 2 but a lower fraction of hard phase, causing a decline in COF but an increase in wear volume. The wear mechanisms of the coating and the substrate were analyzed, the subsurface stress distribution state of the wear scars were further analyzed. The current results present new insights on the anti-wear design strategy to the composite coatings consist of hard and self-lubricating phase. [Display omitted] • The high-temperature fretting wear volume is reduced about 40 times. • The strategy to the addition of the hard and lubricating phase were revealed. • The hard phase has a greater impact on the high-temperature fretting wear. • This work guide for the protection of the titanium alloys. [ABSTRACT FROM AUTHOR]

The synergistic effect of lead-bismuth eutectic (LBE) corrosion and fretting on the damage of a 316 stainless steel was thoroughly investigated. The interaction between the LBE corrosion and fretting plays a key role in materials damage. The dissolution of Ni element leads to a large number of vacancies, lattice defects and built-in internal strain, making the material itself more prone to damage during the wear. Additionally, the shear strain induced by fretting can break the oxide layer formed during friction, leading to the exposure of new materials. This study can provide essential information on damage of heat transfer tubes. [Display omitted] • The dissolution of Ni results in the transformation of the substrate from austenite to ferrite, accelerating the fretting. • Shear strain breaks the oxide layer leading to the exposure of new materials to LBE, accelerating the corrosion. • The synergistic effect between LBE corrosion and fretting accelerates the damage of materials. • This work can rich the data of the investigation on the damage of the heat-transfer tubes in nuclear power plants. [ABSTRACT FROM AUTHOR]