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The composite material sintered by copper and graphite belongs to 'pseudo-alloy', which reduces its self-lubricating performance to a certain extent. Because WS2 and graphite have similar self-lubricating characteristics, the synergistic lubrication mechanism of copper-based graphite-WS2 (Cu-Gr-WS2) has become a hot research topic in recent years. In this paper, the synergistic lubrication mechanism and friction contact surface characteristics of Cu-Gr-WS2 self-lubricating composites under different friction loads were studied. The results show that the friction coefficient first decreases and then increases under the load from 20N to 110N, and the worn surface roughness first decreases and then increases. There is almost no self-lubricating film on the contact surface under small loads. With the load increasing to 80N, the friction coefficient is as low as 0.115, and a continuous and smooth graphite-WS2 self-lubricating film is formed on the contact surface. The main wear mechanism is delamination wear, and the thickness of the lubricating film is about 14.5nm by XPS etching. When the load continues to increase to 110N, there are many adhesion pits on the lubrication film of the contact surface, and the self-lubricating performance decreases.

A bimetallic composite pipe butt joint was prepared by automatic gas tungsten arc welding (GTAW). The microstructure and pitting properties of the joint were investigated. The results show that the microstructure of the joint is columnar crystal, columnar dendrite, and equiaxial crystal. Mo, Nb, and Cr segregate in joint and form Laves and NbC precipitates in the interdendritic. The heat-affected zone (HAZ) becomes the preferred region for pitting due to recrystallization behavior and large and continuous Laves, this was demonstrated by both immersion corrosion and electrochemical experiments. To better understand the pitting behavior of the joint, this study discusses the mechanism of passive film rupture and pitting development, and uses electrolytic corrosion by Nital to simulate the morphology of the initial corrosion pits around the Laves phase.

The effect of two different groove angles on stress corrosion cracking (SCC) sensitivity of welded joints was investigated by electrochemical and SSRT methods, and the fracture surface of tensile specimens was observed by SEM. The electrochemical results show that the corrosion resistance of HAZ region increases with the increase of welding groove angle, while the corrosion resistance of weld region decreases with the increase of welding groove angle. The results of SSRT of the welded joint show that, under the condition of no applied potential, under different welding groove angles (8°/15°), The maximum tensile strength is 546.08 MPa/560.64 MPa, the maximum fracture life is 44.6 h/46.8 h, the maximum elongation after fracture is 9.40%/9.73%, and the maximum reduction of area is 63.53%/65.14%. With the negative increase of applied potential, the SCC sensitivity of welded joint also shows an obvious increasing trend. The fracture morphology of the SSRT tensile test shows that with the negative increase of applied potential, the fracture changes from dimple-like ductile fracture to typical brittle fracture, and obvious stress corrosion fracture occurs.