Molybdenum and its alloys were widely used in machinery, chemical industry, metallurgy, aerospace and other fields because of their high melting point, good heat conduction, good wear resistance and corrosion resistance. The low recrystallization temperature of pure molybdenum leaded to its insufficient high temperature strength and serious brittleness when it returned to room temperature. These shortcomings greatly limited its further application in various fields. For this reason, scholars had developed a series of molybdenum based alloys doped with other elements, among which molybdenum titanium zirconium was the representative. Generally, molybdenum titanium zirconium (TZM) alloy was prepared by methods of vacuum smelting or powder metallurgy, and processed into bars and plates as high-temperature structural materials, which existed several problems in processing difficulties and high temperature friction coefficient. It was necessary to explore the changes of composition and preparation methods to solve similar problems. Doping with self-lubricating Cu can effectively reduce the high temperature friction coefficient of TZM alloy, while the coating prepared by spark plasma sintering (SPS) had the advantages of simple preparation and uniform composition. In this experiment, 304 stainless steel was used as the substrate, pure nickel foil was used as the transition layer, and 30% alloy powder after mechanical mixing was used as the sintering material. The TZM-30Cu alloy coating prepared on the surface of 304 stainless steel by SPS had important development and use value, containing about 30% Cu. The bond strength of the coating was measured using a tensile peel adhesion test; the thermal stability of the coating was tested using a thermal cycle test; the alloy coating and the TZM alloy were tested at 700 ℃ using a friction and wear tester; the coating structure was analyzed by field emission scanning electron microscopy (SEM) and energy spectroscopy (EDS); and the phase composition of the coating was tested by X-ray diffraction (XRD). After the adhesive tensile test, the sample was broken at the joint between the coating and the tensile rod, and no peeling occurred between the parts of the coating, which showed that the parts of the alloy coating were well bonded. The result of SEM and EDS showed that the elements diffused uniformly during the coating sintering process, which meant the effect of sintering was excellent. The bonding between the coating and the transition layer or the transition layer and the matrix was not simply mechanical, but depended on the way of element diffusion to obtain strong bonding strength. The thermal cycle test was performed at 600 and 800 ℃, the coating cracked and fell off along the transition layer, and the coating itself was not cracked and peeled. The main reason for the cracking and peeling of TZM-30Cu alloy coating along the nickel transition layer in the thermal cycle test was the thermal stress caused by the difference of thermal expansion coefficient, and the pitting of Cl- in high temperature water at the interface promoted the cracking and peeling of TZM-30Cu alloy coating.The results of high temperature friction and wear test showed that the wear mechanism of TZM alloy was oxidative corrosion wear and alloy coating was oxidative corrosion wear plus slight adhesion wear respectively. The average friction coefficient of TZM alloy was 0.44, while the average friction coefficient of alloy coating was 0.3, which was about 32% lower than that of TZM alloy. The addition of copper had effective self-lubricating and friction-reducing effects, which was due to the oxidation behavior of Cu in the process of friction and wear at high temperature, and the formation of oxides had self-lubricating effect, which played a role of wear resistance and friction reduction. © Editorial Office of Chinese Journal of Rare Metals. All right reserved.
