Study On The Design,preparation And Tribological Mechanism Of NiAl-Ag₂Mo₂O₇ Composites

Aiming at the problem of friction and wear of mechanical parts at the special working condition,such as elevated temperature and wide temperature in the aerospace,nuclear engineering and metal smelting field,etc.the preparation and tribological properties in wide temperature range of NiAl matrix composites were investigated in this thesis.The silver molybdate powders with different nanostructured morphology?nanowires,nanorods,nanoparticles?were prepared by a hydrothermal reaction method.NiAl intermetallic compound was selected as the matrix,and silver molybdate as lubricating phase.NiAl-based composites were fabricated by high-energy-ball milling/mechanical mixing method proceeded vacuum-hot-pressing sintering.The effects of different nanostructure morphology of silver molybdate on the microstructure,mechanical properties,friction and wear properties of NiAl composites were investigated.The evolution of composition,structure and properties of NiAl-based composites under the wide temperature range from room temperature to 800?were studied,and the mechanism of high temperature lubrication and wear were discussed.The mainly conclusions were followed:?1?Three kinds of silver molybdate powders were prepared by a one-step hydrothermal method with control reaction conditions.The results show that the optimum conditions for the preparation of linear nano-molybdate silver were reaction temperature of 140?,reaction time of 8h,AgNO₃ concentration of0.05mol/L.When the concentration of ammonium molybdate was 0.06mol/L well as the silver nitrate concentration was 0.38mol/L,hydrothermal temperature was 180?and the hydrothermal time was 8h,the morphology was good dispersibility and the particle size was uniform,a diameter of 300nm and a length of 300nm to 1.3?m is obtained.The ammonium molybdate concentration was 0.1mol/L,the AgNO₃ concentration was 0.05mol/L,the reaction temperature was 200?,the reaction time was 8 h,and the structure inducer was PVP,silver molybdate with particle size of about 70-150nm was obtained and the powers with good dispersibility.?2?The NiAl-Ag₂Mo₂O₇ composite powders were fabricated by high-energy-ball milling and the NiAl-Ag₂Mo₂O₇ bulk composites were prepared by vacuum-hot-pressing sintering.The effect of silver molybdate lubricant on microstructure and tribological properties of NiAl-based composites in wide temperature range?RT⁸00??were studied.The results show that the addition of silver molybdate lubricants significantly improved the tribological properties of NiAl-based composites at elevated temperature.In addition,the prepared granular silver molybdate can reduce the friction coefficient and wear rate in a wide temperature range of NiAl-based composites.Compared with linear and rod-shaped silver molybdate,the NiAl-based composites of granular silver molybdate has more excellent tribological properties at 800?,the friction coefficient was 0.27,and the wear rate was 0.46×10^-5mm³/Nm.The improvement of friction and wear properties of composites at elevated temperature is due to the formation of the high-temperature lubricating phase dominated by silver molybdate on the wear surface,which plays a major role in reducing friction and lubrication.?3?The NiAl-Ag₂Mo₂O₇ composite powders were fabricated by mechanical mixing method and the NiAl-based composites with different nanostructures of silver molybdate were prepared by vacuum-hot-pressing sintering technique.The tribological properties in wide temperature range of Ni-based composites containing different nanostructures morphology?nanoparticles,nanowires,nanorods?were investigated.The results show that the three composites of NAW,NAR and NAP exhibit the best tribological properties at 800?.Compared with linear and rod silver molybdate,the NiAl-based composites of granular silver molybdate has more excellent tribological properties at 800?than the linear and rod-shaped silver molybdate.The friction coefficient was 0.16 and the wear rate was only 0.23×10^-55 mm³/Nm.This is attributed to the synergistic lubrication effect of the lubricating film composed of NiO,NiMoO₄ and Ag₂Mo₂O₇ formed on the friction surface at elevated temperature?800??,which reduced the friction coefficient and wear rate of the composite and improved the high temperature tribological properties of the composites.