| Abstract Scope |
The Navy is evaluating solution treated Laser Powder Bed Fusion (L-PBF) Alloy 625 (A625) for various welded applications. Numerous intergranular microcracks roughly 25-100 microns in size were observed throughout the heat affected zone (HAZ) of Gas Tungsten Arc Welded (GTAW) L-PBF A625. Cracking was present in L-PBF A625 material produced by multiple suppliers, using multiple powder lots, and using a range of welding parameters and joint configurations. Gleeble hot ductility testing and elevated temperature tensile testing in the scanning electron microscope (SEM) were performed to evaluate liquation cracking susceptibility, ductility dip cracking susceptibility, and mechanical properties at HAZ temperatures. Testing revealed low ductility in L-PBF A625 relative to wrought A625 at HAZ temperatures. Comparison of the microstructures between wrought and L-PBF A625 revealed significant differences in grain size, primary carbide distributions, and tramp element distributions which could contribute to the observed differences in high temperature ductility. Alternate powder production methods, L-PBF build parameters, heat treatments, and welding conditions were evaluated to determine impact of processing conditions on microstructure and cracking susceptibility. Microstructural characterization was performed using light optical microscopy (LOM), SEM, transmission electron microscopy (TEM), time of flight secondary ion mass spectrometry (TOF-SIMS), and atom probe tomography (APT). Potential causes of microcracking based on these evaluations and potential mitigation methods are provided. |