Effect of ppm-level La modification on hot corrosion behaviour of single crystal superalloy CMSX-4

Doping with trace levels of rare earth elements is an effective approach to enhancing the oxidation and hot corrosion resistance of superalloys. In this study, the hot corrosion behaviour of ppm lanthanum (La) (0 ppm, 40 ppm, and 200 ppm) modified CMSX-4 superalloy and the action micro-mechanism of La were systematically clarified and summarised by SEM, EDS, EPMA, FIB and TEM. The results indicated that ppm-level La doping significantly decreased the corrosion rate of the alloy by more than half. However, increasing the doping level of La does not affect the hot corrosion kinetics of the modified alloys. Compared to unmodified alloys, La-modified alloys exhibit a denser and more complete surface corrosion product, resulting in longer weight gain “plateaus” on the weight gain curves. Further analysis shows La segregation provides a short-circuit diffusion channel for oxygen and promotes the external diffusion of Al, Ti, and Ta, thereby improving the integrity and densification of the protective oxide film. The hot corrosion reaction of the alloy with lower La content (40 ppm) is generally more stable.