Hafnium oxide coating to improve the oxidation behavior of Zirconium Diboride

Abstract

Hafnium dioxide (HfO2) coatings were successfully deposited on zirconium diboride (ZrB2) using reactive magnetron sputtering. After the oxidation at 1500°C or 1600°C, the mutual dissolution of HfO2 and thermally grown ZrO2 was observed which has resulted in the formation of a mixed oxide zone. As the enrichment of the mixed oxide zone by ZrO2 progresses, monoclinic/tetragonal phase transition temperature of ∼1790°C for nominally pure HfO2 moves towards ∼1500 °C. Finally, the inevitable phase transition from monoclinic to tetragonal structure results in the development of cracks, pores, and gaps within the mixed oxide zone. Thickness measurements of the porous ZrO2 scale and the mixed oxide zone of coated specimens revealed an improvent in the oxidation behavior at 1500°C and 1600°C compared to uncoated ZrB2, proving its protective character for short duration oxidation.