Influence of carbon content on microstructure and mechanical properties of Inconel 718 processed with Powder Bed Fusion – Laser Beam

• Additive manufacturing of alloys belonging to the Inconel family is today a hot research topic. Given that these alloys were developed with casting and forging as the main manufacturing route, the possibilities of adjusting their composition to make them better suited for the additive manufacturing processes should be investigated. In this work we study two different versions of Alloy 718 with different carbon content; one having a normal carbon content and one having a very low carbon content. Test pieces from these alloys were produced using the Powder Bed Fusion – Laser Beam process. TEM and SEM with EDS/EBSD was used to study the resulting microstructures both in the as-built and after heat treatment. Mechanical properties were evaluated for samples printed in different build directions using tensile and impact testing. The achieved materials in the as-built condition were very similar to one another in both the microstructure and the displayed mechanical properties. After heat treatment, differences in the microstructures could be identified as secondary carbides were found to precipitate exclusively in the alloy with a normal carbon content. Additionally, the different carbon contents affected the number of annealing twins that formed in the respective alloys, where more twins formed in the alloy with a low carbon content. This was attributed to the alloy’s lower stacking-fault energy. As annealing twins facilitate the transformation of the anisotropic as-built grain structure, effectively making the materials more isotropic, only the low carbon content alloy showed isotropic material properties after heat treatment. 

Ämnesord

TEKNIK OCH TEKNOLOGIER  -- Materialteknik -- Metallurgi och metalliska material (hsv//swe)

ENGINEERING AND TECHNOLOGY  -- Materials Engineering -- Metallurgy and Metallic Materials (hsv//eng)

Nyckelord

Additive manufacturing

Powder Bed Fusion – Laser Beam

Inconel 718

Alloying for additive manufacturing

Mechanical properties

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