| Description |
Additive manufacturing (AM) can produce complex 3D structures that are not obtainable through conventional subtractive machining process. However, AM processing has been shown to create spatially varying microstructures not seen in wrought materials; therefore, the investigation of how microstructural heterogeneity affects as-built material response is crucial to advance understanding of the processing-structure-property relationships. Two approaches to study the observed microstructure heterogeneity in additively manufactured metals have seen interest. The first most commonly used approach varies printing parameters such as laser power, laser scan speed, print layer thickness, and print strategy for individual net-shape specimens. These specimens are then deformed to find relationships between build processing parameters and mechanical properties. The second approach, which is utilized here, uses manufacturer recommended print parameters to print a large volume, followed by specimens being extracted from the build volume and characterization to achieve a global view of the microstructure and mechanical response of the printed volume. The core of the cuboid printed was 81x81x97 mm3 and weighed approximately 5.7 kg, specimens are then extracted from the build volume at selected positions. Depending on the extraction location, the specimen volume has experienced a different thermal history. These thermal history variations result in microstructure heterogeneities within the build volume. This study analyzed the grain properties and texture of as-built and heat treated IN718 specimens extracted along three processing directions namely, the build direction (BD), sweep direction (SD), and transverse direction (TD). Microstructure heterogeneity was clearly observed in the data collected. Columnar grain growth was observed in the SD and TD specimens due to the thermal gradient and layer remelting of successive laser passes. Printing-specific striations were observed in the top of the build volume in the BD resulting in a basket-weave like pattern of near square shaped grains, while BD specimens at the bottom of the build volume did not show these striations due to the numerous heat cycles they experienced. |
