A new strategy to intrinsically protect refractory metal based alloys at ultra high temperatures

•The protectiveness of refractory metal-based alloys can be realized if alloys contain required concentrations of Cr and Ta.•The oxide CrTaO4 reliably protects the refractory equatomic high entropy alloy Ta-Mo-Cr-Ti-Al by formation of a CrTaO4 scale.•CrTaO4 scale forms in a wide temperature range from 500 °C to 1500 °C exhibiting low growth rates.•CrTaO4 possesses high adhesive properties.•Wide stability range of the stoichiometric composition that suppresses the formation of other (non-protective) oxides.