Microstructure And Properties Of Cold Sprayed Copper Matrix Composite Coatings

High performance dispersion reinforced copper alloy has great application potential in new generation information technology,rail transit equipment,aerospace equipment and other fields,and is an important material in many high-tech industries.Cold spraying is an ideal method for preparing dispersion reinforced copper alloys and broadening their application fields because of its low temperature deposition and genetic properties of microstructure.Al₂O₃ dispersion strengthened（ADS）copper and diamond/copper were selected as the research objects.The technological prototype of cold spraying dispersion reinforced copper coating was designed,and the technological feasibility and microstructure evolution of the composite coating were evaluated.（1）Al₂O₃/Cu powder for cold spraying was prepared by internal oxidation.The powder presented sufficient oxidation,compact structure and no alumina shell was formed;Dense ADS copper coating was prepared by cold spray.The combination of two structures,γ-Al₂O₃ nanoparticle dispersion strengthening andα-Al₂O₃ dispersion strengthening with a size of 100 nm,was found in the coating.The powder in the coating experienced great deformation,and the lattice strain reached 0.29%.The coating has both dispersion strengthening and work hardening effects,with a hardness of 185 HV;The conductivity reached 72.5%IACS,which was higher than that of powder metallurgy hot extruded ADS copper;The wear form of the coating is mainly shear fracture of the bulk material along the interface of the laminated structure.The hardness of the powders annealed at 900℃decreased by only 7.2%.The conductivity was increased to82.3%IACS,and the wear rate was reduced by 25%.ADS copper coating has the ability to resist high temperature softening and hinder the interface bonding of powder particles.High temperature annealing can improve the interface bonding of powder particles,so as to improve the conductivity and wear resistance.（2）Diamond/copper powder for cold spray was prepared by spray granulation.The structure of diamond/copper powder was loose and diamond adhered to the surface of copper powder;Dense diamond/copper coatings were prepared by cold spray.During the spraying process,the diamond was not thermally damaged,and the deposition rate was about50%.During cold spray deposition,diamond was fixed in the coating with the rheological behavior of copper,forming a uniform distribution.The main reason for diamond loss during cold spraying is the loose structure of composite powders.The strain of the composite coating is only 0.13%,lower than that of pure copper.The hardness of as-sprayed diamond/copper coating was 149 HV,and the hardness decreased by 36%after heat treatment at 600℃.After annealing,the conductivity of the coating increased from 80.3%IACS to 89.3%IACS;The friction coefficient and wear rate of the coating decreased by 41%.Heat treatment can effectively improve the interface bonding of powders,and the anti-wear effect of diamond can be reflected.