AlPO 4 -C coating deposited by sol-gel technique on Ni base superalloy substrate Nimonic-75 has been examined for high emissivity applications. The coating showed a spectral (2-25 mm wavelength) emissivity in the range of 0?8-0?91, and the emissivity increased with coating thickness. The coating exhibited a reasonably good adhesion with the substrate, as determined from nanoscratch test. The above coating also had a good oxidation resistance in air at 800 and 900uC under cyclic heating and cooling conditions.
Graphitized carbon coated Ni nanoparticles were synthesized in an AlPO4 matrix in situ in an oxidative atmosphere without using any foreign reducing agent.
An aluminium phosphate based high emissivity coating has been deposited on Ni based superalloy C-263 by dip coating method wherein the substrate was immersed in a chemical sol followed by curing of the green coating. Deposition of the coating by spraying the sol on the substrate surface has also been explored. The presence of carbon imparted high emissivity to the coating. Depending on the thickness of the coating, it exhibited an emissivity value of 0?6-0?9 in the wavelength range of 2.5-25 mm. The coating was found to offer good oxidation resistance to the substrate. Cyclic oxidation performance of uncoated and coated substrates has been evaluated at 800 and 10008C for 100 h in air.
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