Search for: All records

The 70/30 copper–nickel alloy is used mainly in critical parts with more demanding conditions in marine settings. There is a need for innovative methods that offer fast production and cost-effectiveness in order to supplement current copper–nickel alloy manufacturing processes. In this study, we employ wire arc additive manufacturing (WAAM) to fabricate the 70/30 copper–nickel alloy. The as-built microstructure is characterized by columnar grains with prominent dendrites and chemical segregation in the inter-dendritic area. The aspect ratio of the columnar grain increases with increasing travel speed (TS) at the same wire feed speed (WFS). This is in contrast with the equiaxed grain structure, with a more random orientation, of the conventional sample. The sample built with a WFS of 8 m/min, TS of 1000 mm/min, and a track distance of 3.85 mm exhibits superior corrosion properties in the 3.5 wt% NaCl solution when compared with the conventional sample, as evidenced by a higher film resistance and breakdown potential, along with a lower passive current density of the WAAM sample. The corrosion morphology reveals the critical roles played by the nickel element that is unevenly distributed between the dendrite core and inter-dendritic area. 

Abstract Wire-arc directed energy deposition (DED) processed Inconel (IN) 718 is known to have coarse columnar grains, strong texture, and significant chemical and microstructural inhomogeneity in the as-fabricated condition. Homogenization treatment is commonly used prior to aging to eliminate the inhomogeneity and detrimental precipitation for better mechanical properties. In this study, however, direct aging (DA) at 700 °C without homogenization has resulted in room-temperature yield strength, ultimate tensile strength (UTS), and elongation that are comparable to wrought condition and among the highest reported properties for wire-arc DED IN718. The DA samples at between 650 and 750 °C aging also demonstrates remarkable ductility when deformed at elevated temperatures. In addition, when aged below 750 °C the DA IN718 possesses significantly higher UTS compared to those with homogenization treatment. These superior mechanical properties are highly likely due to the non-uniform and hierarchical precipitation consisting of disk-shaped γ″ in diameter from a few to tens of nm in the dendritic core area and micron-sized Laves phase and carbides in the inter-dendritic region. 

Abstract Conventional topology optimization presentations generally highlight the numerical and optimization details established on the specially customized discrete geometric modeling system, which is incompatible with the existing computer-aided design (CAD)/computer-aided engineering (CAE) systems. Therefore, tedious preprocessing and postprocessing are required to improve the editability and manufacturability, which are both time consuming and labor intensive. Hence, to address this challenging issue, a novel CAD-based topology optimization system is developed in this work. The following points are highlighted: (i) interoperability issue between CAD and topology optimization was addressed by using macro files to communicate the feature and modeling history information; then, (ii) structural shape and topology optimization is performed based on a B-spline-based approach, which inherits the original spline information from the upstream CAD model and of course, can return spline-based geometric information for optimized CAD model generation, and the last but the most important point to mention is that, (iii) modeling history was incorporated into the optimization process and dynamic modeling history change is enabled based on the optimality criteria. This final point is significant because history-based CAD modeling is still a main-stream approach, especially given the excellent postmodeling editability and design intent capture.