This study examines and compares the microstructures, Vickers microindentation hardness, and mechanical properties for additively manufactured (AM) samples built by a variety of AM processes: wire arc AM (WAAM), electron beam powder bed fusion (EB-PBF), laser wire direct energy deposition (LW-DED), electron beam direct energy deposition (EB-DED), laser-powered direct energy deposition (LP-DED), and laser powder bed fusion (L-PBF). These AM process samples were post-processed and heat-treated by stress relief annealing at 1066 °C, HIP at 1163 °C, and solution annealing treatment at 1177 °C. The resulting microstructures and corresponding microindentation hardnesses were examined and compared with the as-built AM process microstructures and hardnesses. Fully heat-treated AM process samples were mechanically tested to obtain tensile properties and were also evaluated and compared. Principal findings in this study were that high-temperature heat treatment >1100 °C of AM process-built samples was dominant and exhibited recrystallized, equiaxed grains containing fcc {111} annealing twins and second phase particles independent of the AM process, in contrast to as-built columnar/dendritic structures. The corresponding yield stress values ranged from 285 MPa to 371 MPa, and elongations ranged from 52% to 70%, respectively. Vickers microindentation hardnesses (HV) over this range of heat-treated samples varied from HV 190 to HV 220, in contrast to the as-built samples, which varied from HV 191 to HV 304.
Additive manufacturing platforms that rely on thermoplastic feedstock materials are now expected to fabricate components intended for deployment in a wide variety of environments, necessitating an understanding of the ability of a material to perform within a broad range of conditions. The work presented here explored the effect of submerging two polyester materials widely used in fused filament fabrication processes in five common liquid media: distilled water, apple cider vinegar, Mexican Cocacola, 200 proof ethanol and distilled white vinegar for a seven day duration. Mechanical testing, dynamic mechanical analysis and characterization of the fracture surfaces via scanning electron microscopy were used to understand the effect of liquid media exposure. The effects of polymer degradation due to hygroscopic and hydrolytic mechanisms effects were documented. The need for specific procedures for the testing of the environmental effects on the degradation of additively manufactured polymeric components is also highlighted.
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