Intergranular oxidation of additively manufactured Ni-base alloy 625: The role of Si

Abstract

Additively manufactured (AM) Ni-base alloy 625 exposed in air and H2/H2O at 900 degrees C has been shown to suffer from intergranular oxidation attack unlike its conventionally manufactured (CM) variant. Modification of the AM microstructure via hot-rolling and heat-treatment did not alter the oxidation pattern. Detailed analysis of minor differences in chemical composition of AM and CM exposed the critical role of Si in oxidation protection of alloy 625. Experiments with model alloys as well as diffusion modeling confirmed the crucial role of a minimum Si concentration to form a SiO2 subscale preventing thereby intergranular oxidation attack.