MgO coatings doped with aluminum for transmittance yet hard and low emissivity coating on sapphire substrate

In industrial application environment such as temperature measurement and imaging of molten steel, infrared thermal imagers require that their detection windows have good light transmittance, hardness and low emissivity. In this paper, MgO coatings doped with aluminum on sapphire substrate are prepared by magnetron sputtering are studied. After heat treatment at different temperatures, the microstructure of resultant coatings is gradually transformed from amorphous structure to MgAl₂O₄ phase. After heat treatment at 1000 °C, the hardness and modulus of the coatings reached the highest values of 18.42 GPa and 341.2 GPa. At 300 °C, 400 °C and 500 °C, the emissivity of the coated sapphire is significantly lower than that of the uncoated sapphire substrate. The emissivity has a minimum value after heat treatment at 950 °C.