Interfacial diffusion and high-temperature oxidation mechanisms of Cr2AlC MAX-phase coatings on 316L stainless steel: Role of a Cr3C2 diffusion barrier

Cr 2 AlC MAX-phase coatings are considered promising candidates for high-temperature corrosion protection owing to their ability to form protective alumina scales. However, their long-term performance is often limited by interfacial diffusion and structural degradation during thermal exposure. In this work, Cr 2 AlC coatings were deposited on 316L stainless steel by magnetron sputtering using independently controlled Cr, Al, and C targets and subsequently crystallized by vacuum annealing at 700 °C. The oxidation behavior of monolithic Cr 2 AlC coatings and duplex Cr 3 C 2 / Cr 2 AlC architectures was investigated in air at 900 and 1000 °C for 1 h. The monolithic coating exhibited pronounced aluminum depletion, extensive interdiffusion with the substrate, and progressive decomposition of the MAX-phase structure. Oxidation at 900 °C resulted in the formation of Cr 23 C 6 , Cr 7 C 3 , Al 2 O 3 , and Cr 2 O 3 , whereas oxidation at 1000 °C was dominated by Fe 3 O 4 formation due to accelerated iron transport from the substrate. The degradation process was governed by outward aluminum diffusion, destabilization of the layered Cr 2 AlC lattice, carbide evolution within the Cr C subsystem, and subsequent loss of barrier functionality. The introduction of a Cr 3 C 2 diffusion barrier substantially modified the oxidation mechanism by suppressing interfacial mass transport and preserving coating integrity. The duplex architecture maintained a sharp coating/substrate interface up to 900 °C and reduced Fe penetration by approximately a factor of three at 1000 °C. The results demonstrate that Cr 3 C 2 effectively mitigates diffusion-controlled degradation and significantly enhances the high-temperature phase stability of Cr 2 AlC coatings.