Resistance of a Mo–Si–B-Based Coating to Environmental Salt-Based Hot Corrosion

Abstract

During operation of gas turbine engines, different salts develop that lead to a hot-corrosion attack. While the hot corrosion associated with Na₂SO₄ and Na₃VO₄ has received considerable attention, MgSO₄ is also a main salt component, but it has received limited examination. For operation at temperatures beyond the capabilities of Ni-base superalloys, refractory-metal alloys with a Mo–Si–B-based coating have demonstrated a robust environmental resistance including hot corrosion attack by Na₂SO₄ and Na₃VO₄. In order to evaluate the performance of Mo with a Mo–Si–B-based amorphous coating, samples were exposed to MgSO₄ under thermal cycling at temperatures from 800 to 1300 °C. Mass change measurements revealed minimal attack from the MgSO₄ exposure except in local regions where cristobalite and MgMoO₄ were detected. Even with the local region reaction, the mass change after a cumulative 100 h of exposure was about 3.5 mg/cm². Exposure to a composite salt mixture containing Na₂SO₄, NaVO₃, MgSO₄, CaCl, and KCl revealed signs of interactivity compared to the corrosion due to the separate effects of the individual salts, but again the mass change stabilized to a minimal level demonstrating that the Mo–Si–B-based coating is resilient to hot corrosion.