Niobium addition improves the corrosion resistance of TiHfZrNbx high-entropy alloys in Hanks’ solution

•TiZrHfNbx high-entropy alloys are corrosion resistant in a Hanks’ solution at 37 °C.•Nb enhances microstructural homogeneity and passivity of the formed passive film.•Nb reduces donor density thus ensuring the high density and compactness of the film.•Nb accelerates the initiation and progression of passivation process.