As researchers continue to seek the expansion of the material base for additive manufacturing, there is a need to focus attention on the Ni–Cu group of alloys which conventionally has wide industrial applications. In this work, the G-NiCu30Nb casting alloy, a variant of the Monel family of alloys with Nb and high Si content is, for the first time, processed via the laser powder bed fusion process (LPBF). Being novel to the LPBF processes, optimum LPBF parameters were determined, and hardness and tensile tests were performed in as-built conditions and after heat treatment at 1000 °C. Microstructures of the as-cast and the as-built condition were compared. Highly dense samples (99.8% density) were achieved after varying hatch distance (80 µm and 140 µm) with scanning speed (550 mm/s–1500 mm/s). There was no significant difference in microhardness between varied hatch distance print sets. Microhardness of the as-built condition (247 HV0.2) exceeded the as-cast microhardness (179 HV0.2.). Tensile specimens built in vertical (V) and horizontal (H) orientations revealed degrees of anisotropy and were superior to conventionally reported figures. Post heat treatment increased ductility from 20% to 31% (V), as well as from 16% to 25% (H), while ultimate tensile strength (UTS) and yield strength (YS) were considerably reduced.
Al-Cu-Li alloys are famous for their high strength, ductility and weight-saving properties, and have for many years been the aerospace alloy of choice. Depending on the alloy composition, this multi-phase system may give rise to several phases, including the major strengthening T1 (Al2CuLi) phase. Microstructure investigations have extensively been reported for conventionally processed alloys with little focus on their Additive Manufacturing (AM) characterised microstructures. In this work, the Laser Powder Bed Fusion (LPBF) built microstructures of an AA2099 Al-Cu-Li alloy are characterised in the as-built (no preheating) and preheat-treated (320 °C, 500 °C) conditions using various analytical techniques, including Synchrotron High-Energy X-ray Diffraction (S-HEXRD). The observed dislocations in the AM as-built condition with no detected T1 precipitates confirm the conventional view of the difficulty of T1 to nucleate on dislocations without appropriate heat treatments. Two main phases, T1 (Al2CuLi) and TB (Al7.5Cu4Li), were detected using S-HEXRD at both preheat-treated temperatures. Higher volume fraction of T1 measured in the 500 °C (75.2 HV0.1) sample resulted in a higher microhardness compared to the 320 °C (58.7 HV0.1) sample. Higher TB volume fraction measured in the 320 °C sample had a minimal strength effect.
Hot working tool steels (HWTS) are popular for industrial applications such as injection molding tools, and casting dies because of their high wear resistance, fatigue, strength, and toughness properties, even at elevated temperatures. Conventionally, they go through multi-stage heat treatments in order to attain targeted microstructures. Achieving such microstructures with a laser powder bed fusion (LPBF) process will require tailor-made process parameters since it is characterized by non-equilibrium conditions, non-uniform temperature distribution, and metastable phase formation. Recent advances in the LPBF qualification of 1.2343/4 HWTS have shown commendable results but are still fraught with the limitations of poor ductility or extra post-heat treatment steps. For the industrial competitiveness of LPBF HWTS, the enhancement of strength and ductility and elimination of post processing is critical. Therefore, minimizing retained austenite in the as-built samples through pre-heat treatment or alloying to reduce post heat treatments without sacrificing strength will be economically important for industry. In this work, 1.2343 HWTS and its modified form were LPBF printed both in the as-built, pre- and post-heat-treated conditions. The results are discussed based on the correlations of the powder properties with LPBF—part density, microstructure, and mechanical properties.
The long-term sustainability of the Additive Manufacturing (AM) industry not only depends on the ability to produce parts with reproducible quality and properties to a large extent but also on the standardization of the production processes. In that regard, online process monitoring and detection of defective parts during production become inevitable. Optical-based process monitoring techniques are popular; however, most work has been mainly focused on capturing images of print abnormalities without taking other influencing factors, such as camera and part position, chamber illumination, and print geometry on the resolution of the captured images, into account. In this work, we present a scenario to evaluate and quantify the performance of an optical-based monitoring system in a Laser Powder Bed Fusion (LPBF) machine using the F1 score, considering factors such as scan vector orientation, part geometry (size) and position in a built chamber with a fixed camera position. The quantified results confirm that the F1 score can be used as a reliable means of evaluating the performance of optical-based monitoring systems in the LPBF process for the purposes of standardization. The biggest line width of the test artifact (1000 µm) had the highest F1 score range of 0.714–0.876 compared to the smallest (200 µm) with a 0.158–0.649 F1 score.
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