摘要
Abstract
To investigate the changes in the microstructure and properties of Ni-SiC composite coatings when SiC particles gradually transition from the micrometer scale to the nanometer scale,and to analyze the influence mechanism of SiC particles at different scales on Ni-SiC composite coatings.This article uses direct current electroplating to prepare various Ni-SiC composite coatings containing SiC particles of different scales on pure Al discs with a diameter of 20 mm and a thickness of 2 mm,with SiC particles of 3 different sizes(2 μm,500 nm,and 40 nm)as raw materials,through single addition and combination addition methods.
The surface of the Al sheet is polished to 400 grit with sandpaper and an ultrasonic cleaning machine is used to remove grinding debris.The Al sheet is washed with a 70 g/L NaOH solution and then rinsed with deionized water for later use.300 g/L of nickel sulfate(NiSO4·6H2O),45 g/L of nickel chloride(NiCl2·6H2O),and 35 g/L of boric acid(H3BO3)are dissolved in deionized water in sequence,and stirred mechanically to mix evenly,and then added with SiC particles(60 g/L).Mechanical stirring and ultrasonic stirring are conducted to disperse the particles evenly in the plating solution.The plating solution is heated to 50℃and electroplated for 35 minutes to prepare a Ni-SiC composite coating.The anode material used in the electroplating process is an electrolytic Ni plate.After sample preparation,the microstructure of the coating surface and the cross section is observed using a scanning electron microscope(Hitachi S-4800 FE-SEM),and an energy spectrum analysis is performed on selected areas of each coating cross section using an energy spectrometer.Phase detection is conducted on the coating using an X-ray diffractometer(Bruker D8AA25)and the average grain size of the coating metal is calculated.Then,the microhardness of the coating section is measured by a microhardness tester(XH-1000TM),and 5 measurement points are randomly selected to calculate the average value as the microhardness value of the coating.The pin disc friction and wear tester(MMQ-02G)is used to test the room temperature wear resistance of the coating under dry friction conditions.The samples before and after the wear test are cleaned and weighed to calculate the coating wear rate.The corrosion resistance of the coating is tested using an electrochemical workstation(CHI604)in a three electrode system.
As the average particle size of SiC added gradually changes from 2 μm to 40 nm,the preferred orientation of Ni grains in the(200)crystal plane direction in the Ni-SiC composite coating gradually weakens until it disappears.The average grain size of Ni in the obtained Ni-SiC composite coating also decreases continuously with the decrease of the average particle size of SiC added,from the initial 29.8 nm to 15.6 nm.At the same time,the content of SiC in the coating structure gradually increases.The increase of particle phase and refinement of Ni grains in the composite coating further improve the hardness of the composite coating.As the average particle size of the added SiC decreases from 2 μm to 40 nm,the microhardness value of the Ni-SiC composite coating increases from 347.2HV0.1 to 610.6HV0.1,with an increase of 75.9%.This further effectively improves the corrosion resistance and wear resistance of the coating.When the average particle size of SiC is 40 nm,the average friction coefficient and wear rate of the obtained coating are the lowest,at 0.082 and 0.2×10-5 g/(N·m),respectively.Compared with the addition of SiC particles with an average particle size of 2 μm,the average friction coefficient of the coating decreases by 67.1%and the wear rate decreases by 99.2%.关键词
电镀/Ni-SiC复合镀层/颗粒尺寸/显微硬度/磨损/腐蚀Key words
electroplating/Ni-SiC composite coating/particle size/microhardness/wear/corrosion分类
金属材料
