Effect of transition metal on the structure and oxidation behavior of ZrB₂ (0 0 0 1): Experimental and theoretical calculations

ZrB₂ can withstand extreme environments, but the high-temperature oxidation prevented them from being applied as possible thermal protection system materials. The effect of transition metal (Tm = Ta, Hf, Mo, and W) on oxidation resistance of ZrB₂ was systematically investigated by the first principles calculations, including ab initio molecular dynamics, and experimental tests. The results showed that the doped atoms, especially Hf atom, increased the adsorption energy of O atoms, which prohibited the O adsorb on the surface of ZrB₂. Besides, the energy barrier of O atom migration on the Hf-doped surface and inward migration is 0.60 eV and 6.68 eV, which is higher than the un-doped surface. This showed that Hf performs well in inhibiting the diffusion of O. The reason was that the doped atoms increased the strength of B-Zr and O-Zr bonds, respectively. Finally, to verify the theoretical calculations, ZrB₂ and (Zr, Tm) B₂ solid solutions were prepared by using pressure-less sintering and the thermal gravimetric tests were carried out. The experimental results showed that the (Zr, Tm) B₂ solid solutions have better oxidation resistance than ZrB₂, which is consistent with the results from our theoretical calculations. In this work, the modification mechanism of doping atoms on the oxidation resistance of ZrB₂ was explained from the point of view of adsorption and diffusion. And it provides guidance for promoting the application of ZrB₂ at high temperature.