Evolution of in-situ pores and high-temperature thermal-barrier performance of Al-Si coating on NiCoCrAl alloy

A novel method to design and fabricate an in-situ porous Al-Si coating on a NiCoCrAl alloy, by combining hot dip aluminising with heat-treatment techniques, is proposed. Complex in-situ pores and oxides within the coating were controlled by the heat-treatment parameters, and the pore-forming mechanism is discussed. Experimental results showed that the pores formed along the Cr3Si-type particles in the outer layers of the coatings, and grew until they connected with each other to form large pores owing to the Kirkendall effect and oxidation. The thermal conductivity of the coating was tested and compared with other conventional materials. The results showed that the porous microstructure and presence of connected oxides contributed to the low thermal-energy transmission of the coatings.