Synthesis and oxidation behavior of TiAlB (y = 1.7–2.4) coatings

The effect of B concentration on phase formation and oxidation resistance of (Ti 0.35 Al 0.65 )B y coatings with y = 1.7, 2.0, 2.4 was investigated. Elemental B targets in radio frequency mode and a compound Ti 0.4 Al 0.6 target in direct current mode were sputtered. The B concentration was varied systematically by adjusting the applied power to the respective magnetrons, while keeping the power supplied to the magnetron with the Ti 0.4 Al 0.6 target constant. Measured lattice parameters and elastic properties are consistent with ab initio predictions. The oxidation resistance at 700 °C in air for up to 8 h was compared to a cathodic arc evaporated (Ti 0.37 Al 0.63 ) 0.49 N 0.51 coating with an Al/Ti ratio of 1.69 ± 0.20 which is very similar to 1.84 ± 0.40 for the boride coatings. Scanning transmission electron microscopy imaging revealed oxide scale thicknesses of 39 ± 7 and 101 ± 25 nm for (Ti 0.35 Al 0.65 )B 2.0 and (Ti 0.37 Al 0.63 ) 0.49 N 0.51 after 8 h, respectively. Hence, the close to stoichiometric diboride outperforms the nitride coating. This behavior can be understood based on composition and structure analysis of the oxide scales: While the protective layer on the diboride is primarily composed of Al and O, the porous oxide layer on the nitride coating contains Ti, Al and O. • Investigation of the phase formation of (Ti 0.35 Al 0.65 )B y coatings y = 1.7, 2.0, 2.4 • Investigation of the oxidation resistance of these (Ti 0.35 Al 0.65 )B y coatings • Superior oxidation and mechanical properties for the stoichiometric boride coating • DFT data is consistent with all corresponding experimental data.