• Diamond films were successfully synthesized on high-entropy alloy substrates via MPCVD, achieving continuous, uniform, and adherent coatings.
• The diamond/TiZrHfMo sample exhibited excellent corrosion resistance with a corrosion potential of −0.169 V in 3.5wt% NaCl solution.
• A multiple regression model revealed that mixing entropy significantly influences grain size and corrosion properties of the diamond films.
• This work demonstrates the potential of high-entropy alloys as substrates for high-quality diamond film growth, expanding applications in harsh environments.