Preparation And Characterization Of Thermal Protection Coatings Based On Three Dimensional Nickel Structure

In recent years, many countries have given their attention to explor near space vehiles. In this paper, we designed a high thermal emittance structure based on three dimensional photonic crystal for near space vehile to proctect the equipment inside. In the structure designed, three dimensional nickel structure which was also called three-dimensionally ordered macroporous (3DOM) Ni films was prepared on the nickel alloy substrate, which would reflect the light to the top SiC coating to enhance the thermal emittance of the structure. The phase composite, microstructure,suface roughness were investigated by SEM, AFM, XPS, FTIR, Raman spectroscropy and PL spectroscropy. The mechanical properties were ananlyzed by nano-indentation and nano-scratch. The optical properties were studied by UV-Vis-NIR Spectrophotometers. The emissivity of SiC coating was measured by Fourier tranform infrared spectrometer. The influnce of composition, surface roughness and thickness on the emissivity were analyzed.The polystyrene (PS) colloidal crystals have been formed by self-assembly of PS particles using vertical deposition method, in which the PS particles displayed a hexagonal array which indicated the most stable state of thermodynamics. 2D nickle films were get in the plating time shorter than 1min,and 3DOM nickel films were finally obtained in the time longer than 3min, in whcih the pores possesses a face-centred cubic (fcc) crystal structure and no structure shrinkage relative to PS particles during the fabrication process. The pore wall of 3DOM nickel films was smooth which was deposited at 40℃. When the plating temperature above 50℃, the pore wall became rough. The gain size changed with the different plating current density.No abscission and desquamation were observed in the 3DOM Ni films under 10% tensile strains and after nano-scratch test, which suggested that the combination between the nickel PCs and substrate is very stable. And the deformation of the pores less than 10% showed the excellent plasticity. The hardness and Young's modulus of 3DOM Ni films without strain are 0.99 GPa and 23.52 GPa, respectively. And the hardness (0.88 GPa) and Young's modulus (22.68 GPa) of 3DOM nickel PCs with 10% strain are also little smaller than that of 3DOM Ni films without strain. These results imply that the 3DOM nickel PCs on nickel alloy substrate have good mechanical properties. The reflectance of 3DOM Ni films increased as the wavelength increased. And it varied with different current density, in which the reflence of the 3DOM Ni films obtained under 30mA·cm-2 was highest 78%. Cubic YSZ coating was prepared in the 3DOM Ni skeleton when the YSZ precursor was calcined at 600℃for 2h. And the surface of YSZ coating was smooth and compact, which showed us the sizes of particles was similar.SiC coatings were prepared on the Ni alloy substrates by radio frequency magnetron sputtering at low temperature. SiC films were thermal annealed at 300℃,600℃,900℃and 1050℃for 30 min in the vacuum ambient. There were mainly C-Si bonds, C-C bonds, and a small quantity of Si-O bonds, Si-Si bonds on the surfaces of the SiC films. The Si-C bonds were from mainly amorphous SiC and 6H-SiC in small part. And the C-C bonds (sp2) were from amorphous graphite. The surface of SiC coating were smooth and copact. But as the samples were thermal annealed at differernt temperture, the percentages of different bonds were respectively calculated from the peak area and sensitivity factors. The results showed that chemical composition the SiC increased as annealing temperature increased, which suggested the annealing in vacuum was beneficial to the formation of SiC. From the PL spectra, the 6H-SiC were comfired in SiC the films. After annealing, the sizes of particle on the surface SiC coating became larger, and the interface between particles became illegibility. Meanwhile, the surface roughness, hardness and Young's modulus increased.The 3DOM Ni films, YSZ coating and SiC coating was one integrated mass in the thermal protection structure. And the spectral emissivity of SiC films was investigated at 300℃, 500℃, 700℃. The results showed the spectral emissivity of SiC coating increased as the test temperture increased. And at the same test temperture, it increased as the thermal annealing temperture increased. The emissivity of SiC coating were about 0.90 at 700℃. With wavelength, the variations of SiC coatings annealed at the same temperature were different. From all the reasults, The emissivity of the structure was in the relationship of test temperature, chemical composition, surface roughness,and so on.