High Temperature Oxidation of Additively Manufactured Structural Alloys

Abstract

Metal alloys produced by additive manufacturing have specific microstructures and compositions. Their microstructure is generally out of equilibrium, textured, and inhomogeneities can be observed. They can have pores and nano-inclusions. The contents of volatile elements may deviate from the nominal composition. These alloys often experience significant internal stresses and present fairly rough surfaces depending on the process used. Hipping these alloys modifies their microstructure and defects. This literature review shows that open porosity can lead to much higher oxidation kinetics than dense materials, with very deep internal oxide penetrations. Nevertheless, when fabricated with optimized parameters, LBM- or EBM-alloys, such as TA6V, 718, or 316L, can behave as well as, or even better than, wrought alloys. The roughness of the surface is not necessarily problematic, but it can lead to local breakaway phenomena and premature spalling on some alloys. It has been verified that the nature of the grain boundaries strongly affects the intergranular oxidation. The effect of chemical segregations on the protective nature of the outer oxide layer has also been reported. Today, too few studies have been devoted to the effect of raw and pre-oxidized surface states after HIP on cyclic oxidation and on hot corrosion of these alloys.