Effects of Nanometer Al2O3 Particles on Oxidation Behaviors of Laser Cladding Low Al NiCoCrAlY Coatings

Different contents of nanometer Al2O3 particles (nano-Al2O3p) were added into laser cladding low Al NiCoCrAlY coatings to improve the oxidation resistance. The isothermal oxidation behavior of the coatings in air for 100 h at 1050 °C were investigated, and the effects and influencing mechanisms of nano-Al2O3p were discussed. The results showed that oxidation resistances of the nano-Al2O3p-added coatings are clearly better than that of the nano-Al2O3p-free one. The coating with 1 wt% nano-Al2O3p added showed the best performance. Its weight gain was 1.72 mg/cm2 after 100 h oxidation, which was only half the weight gain of the nano-Al2O3p-free coating. The duration required to reach the steady oxidation was only 1/20 that of the nano-Al2O3p-free coating, while the duration of the steady stage was 5 times longer than that of the nano-Al2O3p-free coating. With the addition of nano-Al2O3p, the oxidation resistance was improved by acceleration of Cr selective oxidation, inhibition of volatilization of Cr2O3 scales, improvement of oxide scale self-repairing capability, and blocking of micro channels for oxygen penetrating inwards. In particular, it was inferred that this blocking also has a significant effect on enhancing the oxidation resistance of other high temperature protective coatings such as non-volatile oxide scales.