CT scan, EBSD and nanoindentation analysis of 3D-printed parts with post-process heat-treatment

Abstract

Heat treatment is vital for improving the characteristics of Laser Powder Bed Fusion (LPBF) components. The technique has the potential to change the microstructure of the material as well as its mechanical properties, such as yield strength, hardness, and ultimate tensile strength. To avoid undesirable impacts on the microstructure, temperature, heating, and cooling rates must be precisely controlled. Several parts were printed using LPBF from Steel 316L powder and went through post-process heating. The CT scan analysis revealed that heating the 3D printed parts for 40 min at 900 °C and 950 °C increased the porosity level across the parts although the porosity then decreased after 950 °C. From 850 °C to 1050 °C, EBSD analysis resulted in inverted pole figure maps demonstrating a relative increase in grain size. ImageJ software was used to determine the actual grain size and phase, revealing a grain size growth. Furthermore, as heat treatment temperatures increased, the ferrite phase enlarged. The cellular structure and high temperatures had a major impact on mechanical characteristics. Hardness test findings revealed a decreased mechanical characteristic as heat treatment temperature rose represented by increased porosity population and grain size. To increase the mechanical properties of these materials, an effective strategy is to achieve an even distribution of micro grains while limiting the porosity population.