Effect Of Surface Nanocrystallization And Laser Ladding On The Microstructure And Performance Of Cu-8Cr Alloy

CuCr alloy has the characteristics of high strength and high conductivity,widely used in power transmission,electronic components and other fields.High temperature,environmental corrosion and wear are the main factors leading to the overall failure of the alloy.Corrosion and wear start from the surface,so surface modification is an effective way to prolong the service life of copper alloys.Surface nanocrystallization can greatly improve the hardness,corrosion resistance and wear resistance of metal.Laser cladding treatment can form a metallurgical combining strengthening layer on the metal surface with the matrix.Both of the surface treatment methods can effectively improve the surface properties without affecting the internal microstructure and properties.The combination of these two methods is expected to provide a new idea and reference for material composite surface treatment.Based on this,this paper took Cu-8Cr alloy as the research object,with surface hardness,corrosion resistance and wear resistance as performance evaluation indexes,respectively,using ultrasonic surface rolling and ultrasonic shot peening as surface nanocrystallization methods,surface nano+laser cladding composite surface modification technology for Cu-8Cr alloy surface treatment.The changes of microstructure and properties of the alloy surface before and after treatment were studied,and the mechanism of strengthening was clarified.The results showed that:（1）The pressure drop of ultrasonic surface rolling was optimized,and the optimal pressure drop of Cu-8Cr alloy was 0.15 mm.Under this pressure drop,the hardness of the alloy was increased from 74 HV_0.05 to 121 HV_0.05,and the tensile strength was increased from 261 MPa to 388 MPa.After ultrasonic rolling,a layer of Cu and Cr-rich oxides and Cu（OH）₂ passivation film was formed on the surface of the sample in Na Cl solution,which improved the corrosion resistance of the sample.The wear resistance is improved,and the wear mechanism has no change except that the fatigue wear decreases due to the increase of hardness.（2）Ultrasonic shot peening processing parameters were optimized,and different shot peening particle sizes and time were selected to explore.When the shot peening particle size was 2 mm and shot peening time was 30 min,the alloy hardness increased from 74 HV_0.05 to120 HV_0.05,and the tensile strength increased from 261 MPa to 417 MPa.Elongation decreased from 45%to 32%.With the increase of peening particle size,the surface hardness of the alloy increases,and the corrosion resistance increases first and then decreases.After ultrasonic shot peening,the corrosion resistance and wear resistance of the materials are improved.（3）The optimal process parameters of laser cladding are scanning rate of 100 mm/s and lap rate of 35%.Too slow scanning rate will increase surface cracks,and too low lap rate will cause uneven cladding layer.After ultrasonic shot peening and laser cladding,the hardness,wear resistance and corrosion resistance of the cladding layer are improved,and the wear mechanism of the cladding layer is abrasive wear and oxidation wear.