Preparation And Research Of Cr-Al₂O₃ Composite Coatings

In present, the technology of composite depositing which are more and more widely applied in lots of domains such as industry, national defense, biology and so on. Composite layers having some excellent properties such as high hardness, high wear resistance etc better than single metal and alloys have been obtained by electrodepositing of inert particles in metal coatings.With the combination of excellent properties of chromium matrix and those of particles incorporated, electroplating chromium composite coatings are especially appropriate for protecting some key components from special circumstances .Therefore this field of research is receiving intensive interests of today's surface finishing and engineering communities.This paper mainly introduces the preparation and investigation of Cr/Al₂O₃ layers by co-deposition on stainless steel. This paper prepares two kinds of structured coating by composite electroplating and studies the influence of preparation process on coatings. The influence of technological condition parameters, such as current density of cathode, the temperature of electrolytes, electroplating time and additive etc on the microhardness and wear resistance of pure chromium coatings and the composite coatings were studied elementally. Adding surfactant can improve particle dispersion of nanoparticle in coating. When the temperature 40℃, current density 35 A/dm²,plating time three hours, and the concentration of Al₂O₃ particles 50g/L,the excellent composite coatings can be prepared. The paper also tries to explain the deposition principle of particles composite plating and dispersive theory of surfactant.Pure chromium coatings and Cr/Al₂O₃ composite coatings were prepared. The surface of pure chromium coatings and Cr/Al₂O₃ composite coatings were observed and analyzed by scanning electron microscope (SEM), hardness was evaluated by micro-hardness instrument, frictional wear was tested by friction wear testing machine. The result of comparison indicated that the properties of the coating using nanopowder were not better than those sub- micron powder composite coating.