Research On Surface Modification And Its Mechanism Of Metallic Material By Ultrasonic Machining

In this paper,a new surface treatment technology—ultrasonic machining(USM)technology is used to modify the surface of metal materials(ductile iron and 45 steel).Taking the shaft,plane and engineering samples as examples,the scanning electron microscope(SEM),white light Confocal Laser three-dimensional Scanning Microscope,X-ray diffraction(XRD),universal testing machine,and micro-hardness tester are used to analyze the ultrasonic machining technology.The affects of the surface morphology,microstructure,tribological properties,mechanical properties of metal materials are researched systematically,and the causes are analyzed,parts of mechanisms in ultrasonic machining process are discussed.The foremost research results of this study are as follows:1.By the test of the three-dimensional topography and microscopic geometry of the sample we can find that: the surface three-dimensional topography and microstructure study found that after ultrasonic processing,the surface roughness of the ductile iron materials is significantly reduced,the change rates of Ra of the camber,plane and motor cover are-35.29%,-81.13%,-76.98%;The sizes decreased by-8?m,-10?m,-10?m respectively;There is a bulge with a height of about 30 ?m in the section of dealed and undealed parts on the sample.2.The mechanical test results show that the surface micro hardness of the USM sample is significantly improved,the hardness of ductile iron has increased by 25.5% with an affected layer about 0.6mm to 0.8mm;The hardness of 45 steel has increased by 12% with an affected layer about 1.5mm to 2mm.Ultrasonic processing specimens had lower tensile strength,higher yield strength,and higher yield ratio.The tension-tension fatigue life of the dealed ductile iron can be significantly prolonged,which is synthetically resulted by the grain refinement layer,work hardening,residual compressive stress,and surface morphology etc.3.Under the condition of oil lubrication,the ball/disc frictional tests are conducted,which the ball is GCr15 and the discs are treated or untreated.Contrast tests show that the friction coefficient of USM pair are much smaller than the untreated pair;After USM,the wear capacities of the friction pair are both greatly reduced,and the wear mechanism of the specimen surface is also different.USM could significantly improve the friction reduction,anti-wear properties of the material.4.The vibratory impact of ultrasonic machining caused severe deformation of the surface layer of the metal material,a plastic rheological layer about 100 ?m is formed on the surface of the sample;The plastic deformation of the surface of the material is released through the formation of a new grain boundary and dislocation movement.,eventually grain refinement and surface hardening resulted in the mechanical strengthening of the surface.The finite element simulation analysis found that there is obvious plastic deformation in the feed direction of the ultrasonic tool,and the change trends of the angle and depth are consistent with the microstructural changes observed in the microstructure.