| Copper and copper alloys are widely used in various fields of industrial production due to their excellent properties.But in the high load working environment,parts surface will inevitably appear cracks and corrosion damage.Cold spraying technology has many advantages,such as low spraying temperature,no oxidation phase transformation,powder recovery and utilization,which can be used to repair the surface of damaged parts.However,for the spraying materials with high thermal conductivity,high hardness and easy oxidation,it is difficult to form high quality coating by traditional cold spraying technology.Aiming at the limitation of traditional cold spraying technology,this paper optimized and improved it,and designed a plasma assisted low pressure cold spraying device.High quality copper coating is prepared by plasma-assisted low-pressure cold spraying.At the same time,the coating is analyzed by scanning electron microscopy and energy spectrum,hardness analysis,abrasive resistance analysis,corrosion resistance analysis and annealing.The main research contents and results are as follows:The numerical simulation of the spraying process of plasma-assisted low-pressure cold spraying technology showed that although the plasma assisted device increased the spraying temperature,it did not melt the powder particles,and retained the original characteristics of the traditional cold spraying technology.And increasing the temperature of powder particles,could make the powder particles and matrix collision deformation more fully,make it better embedded in the matrix,get dense coating.At the same time,in the case of a single pass,it could be found that in the case of a single pass,a dense and thick copper coating could be made by appropriately reducing the scanning speed of the spray gun and appropriately increasing the main pressure in the spraying process.Compared with the traditional cold spraying technology,the copper coating prepared by plasma-assisted low pressure cold spraying technology was more compact,and the wear resistance and corrosion resistance of the coating were improved.The optimal process parameters for the plasma-assisted low-pressure cold spraying technique were as follows:the scanning speed of spray gun was 1mm/s and the gas pressure was 0.8MPa.Under this process conditions,the thickness of the coating was 753±23μm,the porosity of the coating was 0.596%,the microhardness was 161.2HV,and the friction coefficient was about 0.12.It could be found that the corrosion rate of the coating was 0.094mg/cm2·h after soaking in 3.5wt.%Na Cl solution for 24h.The self-corrosion potential and self-corrosion current density of the coating were-0.265V and 7.866×10-6A/cm2.The copper coating prepared by plasma-assisted low-pressure cold spraying was annealed at 300℃,500℃and 700℃respectively.When the annealing temperature was 300℃,the coating was compact and the grains in the coating are fine and uniform,and some recrystallization occurs.After heat treatment at 500℃,the coating was more dense and the grain began to grow.After heat treatment at 700℃,the pores in the coating increased,the grains continue to grow,and some twins appeared.With the increase of heat treatment temperature,the microhardness of the coating decreased gradually,the friction coefficient of the coating had little difference,and the time to enter the stable stage increased gradually.Through soaking and electrochemical experiments,it could be found that the corrosion resistance of the coating was significantly improved after annealing at 300℃,which was significantly improved compared with the coating without heat treatment.The corrosion rate of the coating was 0.058mg/cm2·h after soaking in 3.5wt.%Na Cl solution for 24h.The self-corrosion potential and current density of the coating were-0.258V and 3.017×10-6A/cm2. |
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