Investigation Of Ultrasonic Plasma Sprayed NiCr-Cr₃C₂Coating On Mould CrZrCu Alloy

With the continuous development of steel production industry, continuous casting androlling technology were used more and more widely. As the core component of thetechnology, the mold quality directly affected the continuous casting operation rate and thecontinuous casting bloom quality, so the mold surface properties would be higher. Theservice life of the mold without any surface treatment was usually short, in order toincrease the service life of CuCrZr mold, the ultrasonic plasma spraying technology wasused to make Cr₃C₂-NiCr coating, NiAl coating and NiAl/Cr₃C₂-NiCr coating on thesurface of CuCrZr.The orthogonal optimization method was used in coatings’ preparation process to findthe optimum process parameters of ultrasonic plasma spraying. The results showed thatafter the orthogonal optimization, the bonding strengths of the coatings were improved,Cr₃C₂-NiCr coating reached55.85MPa, NiAl coating reached65MPa, NiAl/Cr₃C₂-NiCrcoating reached49MPa.The microstructure, element distribution and the phase composition of Cr₃C₂-NiCrcoating, NiAl coating and NiAl/Cr₃C₂-NiCr coating were investigated by SEM, EDS andXRD. The results showed after the orthogonal optimization, the porosity decreased, and theinterface quality improved. The bonding mode between Cr₃C₂-NiCr coating and CuCrZralloy was mechanical. Differently, the main bonding mode between NiAl and CuCrZr alloywas mechanical, but part of the region had a micro-metallurgical bonding. There were lotsof Cr₃C₂, Cr₂₃C₆, Cr₇C₃and NiCr phases in Cr₃C₂-NiCr coating. The phases ensured theCr₃C₂-NiCr coating had good wear resistance and corrosion resistance. Besides Ni and Alphases, there were Al₄Ni₃, Al₃Ni₂, AlNi3, NiAl intermetallic compounds in NiAl coating.The heat of reaction between Ni and Al was benefit to the melt of NiAl powder.The study of thermal shock performances of Cr₃C₂-NiCr coating and NiAl/Cr₃C₂-NiCrcoating showed the NiAl bonding coating was effective to reduce the thermal mismatchstress, which was caused by the difference in thermal expansion coefficient, betweenCr₃C₂-NiCr coating and CuCrZr alloy. And the thermal shock lifetime of the coating wasimproved.Based on the research of the cross-section microhardness distribution of Cr₃C₂-NiCrcoating, we found the microhardness was scattered, but it obeyed the normal distribution,and the microhardness of the coating was at a high level. It made the coating could effectively improve the wear resistance of CuCrZr alloy.In addition, through the ultrasonic impact treatment, the density, thermal shocklifetime and hardness of the Cr₃C₂-NiCr coating were all improved.