| Surface strengthening treatment is an important method to enhance the surface mechanical properties and corrosion resistance of materials.In the local regions of complex metal components such as offshore platforms,ships,and large engineering machinery,surface treatment methods with flexible operation,convenient on-site application,significant surface strengthening effects,and good corrosion resistance are required.Ultrasonic impact treatment(UIT)is such a technique with the characteristics of easy operation and strong adaptability.It can not only improve the surface stress distribution of the metal component,refine the grain,enhance the surface strength and hardness,but also can form an oxide cladding layer on the surface with the main elements from the impact pins.In the present paper,the ultrasonic impact cladding(UIC)technique was proposed based on the UIT technique.With a large number of experiments,a cladding layer with high hardness and strong corrosion resistance was prepared on the surface of the low-alloy high-strength steel specimen.Through scanning electron microscopy(SEM),X-ray energy spectrum analysis(EDS),X-ray photoelectron spectroscopy(XPS),and other methods,the morphology,element,and composition of the cladding layer were analyzed.The effects of impact intensities,substrate materials,substrate temperature,and impact pin diameter on the cladding were studied.The properties of the cladding under different impact intensities were investigated.The formation mechanism of the cladding prepared by UIC was further revealed.The microstructures,compositions and formation mechanism of the UIC cladding with4 mm diameter titanium alloy pins on the EQ70 high strength steel specimen under different impact intensities were investigated.Results show that the UIC cladding layer is a mixture of oxides with the elements from the impact pins,the parent elements and oxygen in the air,forming by the UIT-induced oxidation effect,the element transfer effect and the effect of "cold melting".The impact intensity is an important factor affecting the thickness and formation of the cladding layer.With the increase of the impact intensity,the thickness of the cladding increases gradually,and the element contents of Ti,Fe,etc in the oxide tend to be stable.Based on Q345 B steel,EQ70 high-strength steel,and DT4 C iron,the effect of parent material on the formation of UIC cladding with 4 mm diameter titanium alloy pin was studied.The results show that UIC technology can generate cladding on the surface of high-strength steel with different strengths.The cladding on Q345 high strength steel is unevenly distributed,while the cladding on EQ70 high strength steel is uniform in thickness and dense in structure.The effects of substrate temperature and pin diameter on the UIC cladding layer were studied.The results show that cracks appeared between the cladding and substrate formed by ultrasonic impact at high temperature,while the cladding layer produced by UIC at room temperature bonds well with the substrate.It is the key to form the UIC that the titanium alloy impact pins are severely plastic deformed and broken into chips.Therefore,10 mm diameter titanium alloy impact pins can not be formed.The surface roughness,hardness distribution,and corrosion resistance of EQ70 high strength steel specimens after UIC treatment were measured by laser confocal microscope,KB 30 S automatic hardness tester,and electrochemical workstation.The results show that the oxide cladding produced by UIC technology can improve the surface roughness,hardness,and corrosion resistance of EQ70 high-strength steel.The main causes for improving the corrosion resistance of the oxide cladding are the UIT-induced grain refinement and nanocrystalline,preferential corrosion of the oxide layer. |
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