Structure and properties of atmospheric plasma sprayed MnO2/VB2 co-doped NiCr2O4 based thermal radiation coatings
摘要
The MnO2 and VB2 co-doped NiCr2O4 coatings（MV） with different ratios of moles are prepared by atmospheric plasma spraying（APS）， and the phase composition， microstructure， infrared emissivity and thermal shock resistance of the coatings are investigated. The results show that the co-doping of NiCr2O4 with MnO2 and VB2 can more effectively improve the infrared emissivity of the coatings than the doping of MnO2 or VB2， thus the coating with MnO2 and VB2 doping ratio of 1∶1 （MV11） has the highest emissivity. In the 0.75-2.5 μm wavelength ranges， the room temperature band emissivity of the MV11 coating is 0.928， and in the 2.5-25 μm， the infrared emissivity of the coating increases from 0.884 at room temperature to 0.918 at 1000 ℃. It is mainly attributed to the transition metal ions and B ions enter the spinel lattice， increasing the concentration of oxygen vacancy in the lattice， introducing partial energy levels into the bandgap， and causing lattice distortions， enhancing free carrier transition absorption and infrared lattice vibration absorption. In addition， after 30 thermal cycles of water cooling at 25-750 ℃， microcracks appear in the coating， but the phase structure did not change significantly， and the emissivity decreases slightly， indicating that the coating has good thermal shock resistance.