Effect of post heat-treatment on the microstructure and high-temperature oxidation behavior of precipitation hardened IN738LC superalloy fabricated by selective laser melting

The present study investigated the effect of as-built and post heat-treated microstructures of IN738LC alloy fabricated via selective laser melting process on high temperature oxidation behavior. The as-built microstructure showed fine cell and columnar structure due to high cooling rate. Ti element segregation was observed in inter-cell/inter-columnar area. After post heat-treatment, the initially-observed cell structure disappeared, instead bimodal Ni₃(Al, Ti) particles formed. High temperature (1273 K and 1373 K) oxidation test results showed parabolic oxidation curves regardless of temperature and initial microstructure. The as-built IN738LC fabricated via the selective laser melting process displayed oxidation resistance similar to or slightly better than that of IN738LC fabricated via wrought or cast process. Heat-treated SLM IN738LC, although had similar oxidation weight-gain values to those of the SLM as-built material at 1273 K, showed relatively better oxidation resistance at 1373 K. Bimodal Ni₃(Al, Ti) precipitate formed in the post heat treatment changed the local chemical composition, thereby led to changes in alumina former/chromia former location and fraction on the alloy surface. It was concluded that in heat-treated IN738LC increased alumina former fraction was found, and this resulted in excellent oxidation resistance and relatively low weight-gain.