Research On Surface Metallization Of Al₂O₃ And SiC Ceramic Substrate By Cold Spraying

In the fields of electronic information,energy transportation,aviation,and ceramic parts are required to achieve the functions of conductivity,heat dissipation,and packaging.Surface modification technologies such as physical vapor deposition,Mo-Mn method,magnetron sputtering,and electroless plating can be used to coat metal coatings on ceramic surfaces to meet the application requirements.However,the properties of ceramic and metal materials are very different,and the connection between the two should consider reasons such as the poor wettability of ceramics,so the quality of the coatings prepared by the above techniques is poor.The emerging cold spray technology is considered to be a mature method for rapid fabrication of coatings,which can effectively solve the problem of metallization of ceramic surfaces.At present,the domestic research on the bonding mechanism of cold sprayed ceramic metallization is still in the primary stage,and the study found that heat treatment can well improve the bonding strength between the metal coating and the ceramic substrate,it also improves the physical properties of the coating.In the paper,the effects of cold spraying process parameters and substrate state on ceramic metallization quality are deeply studied,which is helpful to promote the study of cold spraying ceramic metallization bonding mechanism.In the paper,Al-Al₂O₃ coating and Cu coating were prepared respectively on the surface of Al₂O₃ ceramic substrate and Si C ceramic substrate by cold spraying technology.The effects of cold spraying temperature and ceramic surface roughness on the coating properties were studied and analyzed to explore the appropriate spraying process and ceramic surface state.The following innovative works have been done in the paper:(1)Al metal coatings were prepared on Al₂O₃ ceramic surfaces with different roughness by using different cold spraying temperatures,and Al₂O₃ ceramic reinforcing phase was added to the sprayed powder to increase the bonding strength of the coating.Cu coatings were prepared on Si C ceramic surfaces with different roughness by using different cold spraying temperatures.The properties of Al-Al₂O₃ coating and Cu coating were characterized by SEM,EDS,XRD,pull-out test,and oxygen element analysis test.(2)The test results show that the porosity of Al-Al₂O₃ coating and Cu coating is low,and the coating is closely combined with the substrate.There is no noticeable oxidation of the coating in the spraying process.When the surface roughness of ceramic substrate is consistent,the bonding strength of the Al-Al₂O₃ coating increases with the increase of the spraying temperature.At the same temperature,the bonding strength between Al₂O₃ceramic substrate and Al-Al₂O₃ coating increases with the increase of ceramic surface roughness.Since the internal bonding force of the Sic ceramic substrate is lower than the bonding strength between the Cu coating and the substrate,the fracture occurs at the substrate during drawing.The conductivity of cold sprayed coating was tested by four probe tester and conductivity meter.The conductivity of Al-Al₂O₃ coating and Cu coating increased with the increase of spraying temperature.The ceramic surface roughness will not affect the microhardness of the coating.With the increase of spraying temperature,the microhardness of Al-Al₂O₃ coating increased from 136.9HV₁₀₀ to 171.0HV₁₀₀,and that of Cu coating increased from 116.5HV₁₀₀ to 139.9HV₁₀₀.(3)Al-Al₂O₃ coating and Cu coating were heat-treated at 600?for 2 hours.The effects of heat treatment on the microstructure,microhardness,electrical conductivity,bonding strength,and oxygen content of cold sprayed Al-Al₂O₃ coating and Cu coatings were studied.The test results show that the bonding strength of the Al-Al₂O₃ coating increases by about 15±5Mpa compared with the sprayed state,but the microhardness decreases to a great extent,and the decrease range is 50±5HV₁₀₀.The hardness of the Cu coating also decreases significantly.For example,the hardness of Cu1 coating decreased from 116.5HV₁₀₀to 64.1HV₁₀₀.The analysis of EDS and oxygen content showed that the oxidation degree of the two coatings increased after heat treatment.Through the analysis of the conductivity test results of the coating,it can be seen that the conductivity of the Al-Al₂O₃ coating increases by about 1 MS/m after heat treatment,and the conductivity of the Cu coating increases by about 30 MS/m.