Achieving superior corrosion resistance in Mo-modified CoNiCrAlTi high-entropy alloys via optimized L12 precipitate distribution and DFT-guided passive film design

Mo addition (2 at.%) to a CoNiCrAlTi high-entropy alloy fundamentally transforms its chloride corrosion behavior through two intrinsically coupled ways. Structurally, Mo suppresses intergranular discontinuous L12 precipitation, disrupting the continuous cathodic network that drives rapid galvanic attack. The resulting finely dispersed intragranular L12 morphology confines corrosion to isolated pitting events. Chemically, Mo6+ catalyzes formation of a dense, well-stratified Cr2O3-MoO3 composite passive film with reduced defect density and active pH-buffering self-healing capability via MoO42−. These coupled mechanisms reduce corrosion current density by two orders of magnitude (to 5.4 × 10−8 A/cm2), elevate the pitting potential by 336 mV, and dramatically improve repassivation kinetics. First-principles calculations corroborate the enhanced passive film stability, revealing that Mo doping increases the oxygen vacancy formation energy on Cr2O3 (0001) from 4.569 eV to 6.381-6.591 eV, elevates Cl− adsorption energy from-0.036 eV to 1.189-1.205 eV, and induces Mo 4d-O 2p-Cr 3d orbital hybridization that strengthens metal-oxygen bonds. These findings establish optimized precipitate spatial distribution, rather than precipitate elimination, as the central microstructural design principle for achieving high corrosion resistance in L12-strengthened HEAs.