Preparation Of Al₂O₃ Nanofluids And Application In The Process Of The Internal-cooling Grinding

Nickel-based superalloys are widely used in the manufacture aerospace engines and the hot end parts of gas turbines due to its excellent high temperature strength,corrosion resistance and stability.However,the service life of the grinding wheel and the surface quality and dimensional accuracy of the workpiece are seriously affected during the grinding process due to the low heat exchange efficiency and poor lubrication performance of the conventional coolant.Nano-fluid regard as a new type of high-efficiency heat transfer lubrication medium with high thermal conductivity,good anti-wear and anti-friction performance and load-bearing capacity,which can achieve better cooling and lubrication effects.It is often widely applied to the grinding process field used as a cooling lubricant.In the traditional grinding,the external cooling of the cooling medium is adopted,however,the heat exchange and lubrication effects of the coolant cannot be effectively realized.The internal cooling grinding method make the cooling medium spray to the grinding arc area from the inside of the grinding wheel,which becomes a positive and helpful try for enhancing heat transfer during the grinding processing.Therefore,the application of nanofluids as cooling lubricants medium in the internal cooling grinding process of high-temperature alloy is of great significance for the realization of high-efficiency and high-quality grinding of nickel-based superalloys.In this dissertation,Al2O3 nanoparticles with high heat transfer capacity and high load carrying capacity were added to soybean oil,and a uniform and stable soybean oil Al2O3nanofluid suspension was prepared by combining physical and chemical methods,which was regard as a cooling liquid to be applied to experimental study of grinding the nickel-base superalloys by utilizing the internal cooling method.And the influence characteristic on the grinding temperature of nickel-based alloy and surface integrity of the workpiece in the internal cooling grinding process were investigated.The main contents of this dissertation are as follows:（1）Under a constant temperature water bath conditions,combining with magnetic stirring and ultrasonic vibration,a two-step method was adopted to prepare soybean oil-based Al2O3 nanofluid oil samples.And the influence of four kinds of surfactants such as sodium dodecyl benzene sulfonate（SDBS）,sodium dodecyl sulfate（SDS）,polyethylene glycol 600（PEG600）and Span80 on the dispersion and stability of Al₂O₃ nanoparticles in soybean oils were investigated.According to sedimentation method and photometer method,a surfactant having an optimum dispersion effect was selected,and then different mass fraction Al2O3nanofluids oil samples were prepared.（2）The contact angle of Al2O3 nanofluid oil samples with different mass fractions on the nickel-base superalloy substrate were measured by utilizing a contact angle measuring instrument,and the influence of the concentration of Al₂O₃ nanoparticles on the wetting properties of nanofluids were analyzed.Based on the planar heat source method,the thermal conductivity of 2.0wt%nanofluids and soybean oil were measured at different temperatures by thermal characteristic analyzer.The viscosity at different temperatures were tested by a viscometer,and the influence of Al₂O₃ nanoparticles and temperature on the thermal conductivity and viscosity of nanofluid and soybean oil were investigated.The tribological performance experiments of different mass fractions of Al₂O₃ nanofluids was conducted by using HRS-2M high-speed reciprocating friction tester,and the mass fraction of nanofluid with the best antifriction effect as well as the best antiwear ability was optimized.At the same time,the surface of the workpiece was observed and EDS analyzed by utilizing a scanning electron microscopy,and the wear-resisting and anti-friction mechanism was explained in detail.（3）The prepared Al₂O₃ nanofluid grinding fluid were adopted to conduct the internal cooling grinding experiment of nickel-base superalloy.Under the same grinding parameters,the influence law of Al₂O₃ nanofluid,traditional coolant and pure soybean oil on grinding temperature and the surface integrity of the machined surface workpiece were compared and analyzed.The heat transfer capacity and lubrication effect of Al₂O₃ nanofluids were explored.The antiwear mechanism of Al₂O₃ nanoparticles during grinding was analyzed.