Microstructure and Microhardness of Wire Flame Spraying Nitinol Coating

One promising area of application of flame spray technology is to obtain corrosion-resistant coatings with adaptive properties of the environment. These include and coatings based on shape memory alloys. The paper presents the results of studies on the formation of metal coating from the wire materials based on NiTi by wire flame spraying method. Spray gun "TERKO" used for flame spraying. A thermal sprayed nitinol coating was produced from  Ti_49.6Ni_50.4. shape memory wire. Spraying was carried out in three stages on carbon steel substrate to prevent excessive heating and the emergence of thermal stress in the coating. The coating surface temperature for the first pass was 150°C, in the other - 80°C. The coating thickness was 700 to 800 microns. The particle size of the sprayed coating that depends mainly on the spray material in this case was in the range from 5 to 30 microns. Coating is formed by melting the wire and particle formation under conditions of intensive interaction with the spray torch, and the subsequent installation of molten droplets in the layer. X-ray diffraction studies indicate that the coating material meets NiTi located in a martensite state. The obtained sprayed coating has lower oxygen content for the wire flame spray process compared to the oxygen content of the powder coating. This is important to get a tight corrosion-resistant coating. The micro-hardness had non-monotonic behavior in the vicinity of the interface between the substrate and the coating. The microhardness of the coating increases at 450 to 600 HV from the distance from the interface.