Texture and Microstructural Features at Different Length Scales in Inconel 718 Produced by Selective Laser Melting

Area of Science:

• Materials Science
• Metallurgy
• Additive Manufacturing

Background:

• Inconel 718 is suitable for selective laser melting (SLM).
• The SLM process results in a complex and heterogeneous microstructure in Inconel 718.
• Understanding the as-built microstructure is crucial for effective post-processing heat treatments.

Purpose of the Study:

• To investigate the microstructural features of as-built SLM Inconel 718 at multiple length scales.
• To analyze grain morphology and crystallographic texture.
• To understand the solidification mechanism and its impact on microstructure.

Main Methods:

• Optical Microscopy (OM)
• Scanning Electron Microscopy (SEM)
• Transmission Electron Microscopy (TEM)
• Electron Backscatter Diffraction (EBSD)

Main Results:

• Observed elongated grains in the build direction, unaffected by laser tracks or melt pools, indicating epitaxial growth.
• Identified columnar dendrites within grains, aligned with the thermal gradient along <100> axes.
• Detected microsegregation, interdendritic precipitates, and dislocations at the dendrite scale, with a prominent <100> crystallographic texture.

Conclusions:

• Epitaxial growth driven by the thermal gradient dictates the microstructure of SLM Inconel 718.
• The resulting microstructure exhibits significant <100> crystallographic texture and dendritic morphology.
• Detailed microstructural characterization is essential for optimizing heat treatments of additively manufactured Inconel 718.