An Assessment Study on the Quality of Ni-Cr Coating Before and After Heat Treatment

This paper presents the results of research to assess coating quality before and after heat treatment. The spraying material used here is a mixture of Ni-Cr powder with 80% Ni and 20% Cr. By theoretical analyzes, the combustion of a powder mixture, the movement of liquid metal particles on the metal surface and the adhesion process of liquid metal particles on the metal surface have been determined. Experimental results show that after performing the spraying process on the surface of the part, forming a metal layer of spraying coating on the surface. In addition, if the coating is pre-heat treated on a metal surface, there will be a boundary layer separating the metal coating from the base metal. After carrying out the heat treatment process by diffusion annealing method, there has been diffusion between spraying layer and base metal, creating a link between coating metal and base metal; In addition, the appearance of carbides by diffusing carbon from the base metal to the outside creates the carbides to increase the abrasion resistance for coating. The structural assessments are concretely demonstrated by the results of mechanical evaluation: If before the process of heat treatment, the hardness value of the spray coat was only 191HV, after spraying it could reach the average value of 340HV; There are positions of carbides that can reach 980HV. The adhesion value of the coating can reach 29Mpa after heat treatment and the abrasion intensity of the coating is 1.89x109kg / Nm which is only about one third of the coating without heat treatment.