The Study Of Properties Of HVAF Sprayed Cr₃C₂-NiCr Composite Coatings On CrZrCu Substrate

Cr₃C₂-NiCr coatings were sprayed on mold copper plate by high velocity air fuel technique in this paper.Scanning electron microscopy,optical microscopy,wear tester were used to investigate the effect of bond coats and annealing treatments on micro-structure,adhesion strength,fracture toughness,wear resistance of sprayed coatings.Moreover,the dynamic polarization experiment was used to study the corrosion resistance of sprayed coatings also.Some conclusions were listed as:?1?Compared with HVOF sprayed Cr₃C₂-NiCr coating,HVAF sprayed coating performed better at adhesion strength,hardness and porosity.The wear rate of HVAF sprayed coating was close to HVOF sprayed coating at 400 ?.However,HVAF sprayed coating has superior corrosion resistance than HVOF sprayed coating.The higher adhesion strength and low porosity of HVAF sprayed coating leads to better thermal fatigue resistance.?2?The addition of bond coats can improve the wear resistance and corrosion resistance of composite coatings.The composite coating with NiCr bond coat shows higher hardness,wear resistance and corrosion resistance than the composite coating with NiAl bond coat.But the adhesion strength of NiCr bond coat with substrate was lower than NiAl bond coat.The addition of bond coat can delay the extending of crack under high temperature surroundings.Moreover,NiCr/Cr₃C₂-NiCr bi-layer has better thermal fatigue resistance than NiAl/Cr₃C₂-NiCr bi-layers.?3?Annealing treatment improved the metallurgical adhesion of NiAl and NiCr bond coat with Cr Zr Cu substrate.The depth of diffusion zone improved with the increase of annealing temperature.However,the heat release from the Ni-Al reaction results in the decrease of adhesion strength between NiAl bond coat with work layer.The HVAF sprayed bi-layers under 600 ? annealing treatment present the best wear resistance and corrosion resistance;Moreover,the wear resistance and corrosion resistance of annealed coatings increased first and then decreased with the increase of annealing temperatures.?4?Annealing treatment caused primary carbides precipitate the secondary carbides to molten NiCr particle.The size of secondary carbides increased with the increase of annealing temperature,which caused the hardness,wear resistance and corrosion resistance increased first and then decreased.