Investigation of Ultrasonic Plasma Sprayed NiCr-Cr3C2Coating on Mould CrZrCu Alloy
Cui Ting
CNKI
Abstract
With the continuous development of steel production industry, continuous casting and rolling technology were used more and more widely. As the core component of the technology, the mold quality directly affected the continuous casting operation rate and the continuous casting bloom quality, so the mold surface properties would be higher. The service life of the mold without any surface treatment was usually short, in order to increase the service life of CuCrZr mold, the ultrasonic plasma spraying technology was used to make Cr3C2-NiCr coating, NiAl coating and NiAl/Cr3C2-NiCr coating on the surface of CuCrZr.
The orthogonal optimization method was used in coatings' preparation process to find the optimum process parameters of ultrasonic plasma spraying. The results showed that after the orthogonal optimization, the bonding strengths of the coatings were improved,Cr3C2-NiCr coating reached 55.85 MPa, NiAl coating reached 65 MPa, NiAl/Cr3C2-NiCr coating reached 49 MPa.
The microstructure, element distribution and the phase composition of Cr3C2-NiCr coating, NiAl coating and NiAl/Cr3C2-NiCr coating were investigated by SEM, EDS and XRD. The results showed after the orthogonal optimization, the porosity decreased, and the interface quality improved. The bonding mode between Cr3C2-NiCr coating and CuCrZr alloy was mechanical. Differently, the main bonding mode between NiAl and CuCrZr alloy was mechanical, but part of the region had a micro-metallurgical bonding. There were lots of Cr3C2, Cr23C6, Cr7C3 and NiCr phases in Cr3C2-NiCr coating. The phases ensured the Cr3C2-NiCr coating had good wear resistance and corrosion resistance. Besides Ni and Al phases, 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-NiCr coating showed the NiAl bonding coating was effective to reduce the thermal mismatch stress, which was caused by the difference in thermal expansion coefficient, between Cr3C2-NiCr coating and CuCrZr alloy. And the thermal shock lifetime of the coating was improved.
Based on the research of the cross-section microhardness distribution of Cr3C2-NiCr coating, 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 shock lifetime and hardness of the Cr3C2-NiCr coating were all improved.
Key words: ultrasonic plasma spaying; CuCrZr alloy; Cr3C2-NiCr coating; orthogonal test;ultrasonic impact treatment
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