Abstract Scope |
Metal powders are a prominent feedstock used for fusion-based additive manufacturing processes. Even though they are produced within the same compositional limits as their wrought counterparts, they are prone to the pick-up of interstitial elements, such as nitrogen and oxygen, as well as small variations in minor alloying elements. These small alloying element variations usually fall within allowable specified limits but also impact the microstructural evolution during both additive manufacturing and post-process heat treatments. Through the study of a range of stainless steels and nickel base alloys, these small variations were found to lead to the formation of phases not observed in the wrought materials and drive significant changes in the microstructural evolution and resulting properties during additive manufacturing. For example, high oxygen levels in stainless steels drive the formation of oxygen-rich inclusions that impact microstructural formation, mechanical properties, and corrosion behavior. Solid solution strengthened nickel base alloys were also influenced by high nitrogen levels that drove the formation of nitride-based phases in the as deposited condition and persist through post-processing. In these complex multi-component alloys, the identification of simple alloying element interactions is insufficient and does not identfiy the fundamental process-structure-property relationships needed to design new alloys or adapt existing ones to the additive manufacturing process. Emerging computational tools are being combined with in situ and ex situ high resolution characterization techniques to identify these phases and build databases for predicting microstructural evolution and material properties and performance. |