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In this work, a novel optimization approach is introduced to extract combined hardening parameters from the cyclic stress-strain data obtained from the initial hardening cycles of isothermal, low-cycle fatigue tests. The incremental elastic-limit (IEL) concept is proposed due to the often-undiscernible elastic range of a stabilized stress-strain cycle, that increases the complexity of hardening parameters optimization. The optimization process is implemented by taking an iterative search for the elastic range by a fixed elastic limit increment, and the corresponding hardening parameters are obtained using the nonlinear fitting algorithms in the MATLAB™ Software. An implicit stress-update function is introduced to simulate the cyclic stress and strain with a given set of hardening parameters and yield strength. The fitness of the optimization is calculated based on the least square difference between the experimental and simulated stress-strain data. Furthermore, the IEL concept is incorporated to optimize the cyclic hardening parameters. In the final step, finite element (FE) analysis using the optimized hardening parameters is applied to demonstrate the effectiveness of the IEL approach. The proposed methodology is applied to pressure vessel steels and Ni-based weld metals. 

Nickel-based alloys, Alloys 625 and 718, are widely used in the aerospace industry due to their excellent corrosion resistance and high strength at elevated temperatures. Recently, these alloys have been utilized to manufacture rocket engine components using additive manufacturing (AM) technologies such as laser powder bed fusion (LPBF) and powder-blown laser-based directed energy deposition (DED). These technologies offer faster and more cost-effective production while enabling the fabrication of near-net-shape parts that are subsequently joined by welding. However, solidification cracking susceptibility varies significantly between AM and conventionally processed materials, and limited weldability characterization has been conducted on AM-fabricated materials. This study assesses the weld solidification cracking susceptibility of Alloys 625 and 718 produced by wrought (mill-rolled), LPBF, and DED using transverse varestraint testing, Scheil-Gulliver simulations, the Crack Susceptibility Index (CSI), and the Flow Resistance Index (FRI). Transverse varestraint testing revealed that AM parts exhibited higher susceptibility due to the presence of larger and elongated grains in the fusion zone, affecting the weld solidification cracking response. In Alloy 625, the LPBF condition exhibited the highest maximum crack distance (MCD) of 2.35 ± 0.16 mm, compared to 1.56 ± 0.06 mm for wrought and 1.72 ± 0.10 mm for DED. Similarly, in Alloy 718, the DED condition showed the highest MCD of 2.93 ± 0.41 mm, while the wrought condition had an MCD of 2.01 ± 0.12 mm, and the LPBF condition reached 3.01 ± 0.33 mm at 5 % strain, without a clearly defined saturation strain. Although wrought materials demonstrated greater resistance to solidification cracking, solidification simulations did not correlate with the experimental testing, as they do not account for microstructural and mechanical factors, relying solely on chemistry. 

The use of laser powder bed fusion (LPBF) for faster and more customized manufacturing has grown significantly. However, LPBF parts often require welding to other components, raising concerns about their weldability due to differences in microstructure compared to conventionally manufactured parts. Despite its importance, research on the weldability of additive manufacturing materials remains limited. This study aims to evaluate the susceptibility of LPBF 316L stainless steel to weld solidification cracking using transverse varestraint testing and compare results with conventional 316L. Tests were conducted across strain levels from 0.5 to 7%, revealing a saturated strain of 4%, with maximum crack length (MCL), maximum crack distance (MCD), and total number of cracks (TNC) of approximately 0.36 mm and 31, respectively. Compared to existing literature, LPBF 316L produced with optimized printing parameters and low nickel equivalent content exhibited higher resistance to weld solidification cracking, reflected in lower MCL and MCD values. Cracks initiated at the solidus interface and propagated along the ferrite–austenite boundary under strain. Microstructural changes were observed after testing, transitioning from cellular austenitic solidification in LPBF to a skeletal ferrite-austenitic mode due to material remelting and slower cooling rates. These findings highlight that reduced nickel equivalent, alongside optimized printing parameters, contribute to enhanced weld solidification cracking resistance in LPBF 316L. This study advances understanding of the weldability of LPBF materials. 

Restoring components in the hot gas path of turbine engines after service-induced degradation is crucial for economic efficiency. This study investigates the printability of Rene 65 powder on a degraded first-stage turbine blade using two additive manufacturing techniques: Laser Powder Bed Fusion (L-PBF) and Laser Powder Directed Energy Deposition (L-DED). Deposited material was evaluated using optical microscopy (OM), scanning electron microscopy (SEM), and Electron Backscatter Diffraction (EBSD) to characterize its crystallographic texture, while microhardness testing provided insight into its mechanical properties. Our results show that L-PBF excels at replicating intricate features, such as small cooling holes, and produces a highly texturized microstructure oriented parallel to <001> under optimal parameters (80 W, 400 mm/s, unidirectional scanning), although at a slower pace. In contrast, L-DED offers a versatile, rapid, and cost-effective method for repairing medium to large parts, yielding an equiaxed microstructure and higher as-printed hardness—approaching GTD 111 values due to an aging effect from high heat input. Both processes effectively restored the dimensional integrity of degraded blade tips, paving the way for more sustainable and economical maintenance strategies in the aerospace industry. 

Wire arc additive manufacturing (WAAM) is an effective technique for producing medium to large-size components, due to its convenience and sustainability in fabricating large-scale parts with high deposition rates, employing low-cost and simple equipment, and attaining high material efficiency. Thus, WAAM attracts different industrial sectors and has experienced great growth, particularly over the last decade to overcome production market’s challenges. Consequently, fabricating parts in WAAM, mostly resulted in heterogeneity in microstructure of three different zones towards the buildup direction due to different cooling rates; upper zone (thin surface layer of fine grains), middle zone (undesired large columnar grains covers 90% of the produced part), and lower zone (intermediate columnar grains close to substrate material). Accordingly, producing parts consisting of different zones affects the final component's mechanical properties. Therefore, controlling the formation of these zones is a key role in improving WAAM technique. Altering torch motion and cooling rates were found to be effective methods to control the homogeneity of the final component in WAAM. 

Abstract Wire arc additive manufacturing (WAAM) is an efficient technique for producing medium to large‐size components, due to its accessibility and sustainability in fabricating large‐scale parts with high deposition rates, employing low‐cost and simple equipment, and achieving high material efficiency. Consequently, WAAM has garnered attention across various industrial sectors and experienced significant growth, particularly over the last decade, as it addresses and mitigates challenges within production markets. One of the primary limitations of WAAM is its thermal history during the process, which directly influences grain formation and microstructure heterogeneity in the resulting part. Understanding the thermal cycle of the WAAM process is thus crucial for process improvement. Typically, fabricating a part using WAAM results in a microstructure with three distinct zones along the build direction: an upper zone (thin surface layer) with fine grains, a middle zone dominated by undesirably long and large columnar grains covering more than 90% of the produced part, and a lower zone with smaller to intermediate columnar grains closer to the substrate material. These zones arise from variations in cooling rates, with the middle zone exhibiting the lowest cooling rate due to 2D conduction heat transfer. Consequently, producing a component with a microstructure comprising three different zones, with a high fraction of large and long columnar grains, significantly impacts the final mechanical properties. Therefore, controlling the size and formation of these grain zones plays a key role in improving WAAM. The aim of this work is to investigate the formation of undesired columnar grains in austenitic stainless steel 316L during WAAM and propose a simple hybrid technique by combining WAAM with a hot forging process (with or without interlayer cooling time). This approach targets the disruption of the solidification pattern of columnar grain growth during deposition progression and aims to enhance the microstructure of WAAM components. 

Additive manufacturing (AM) has the potential for improving the sustainability of metal processing through decreased energy and materials usage compared to casting and forging. Laser powder bed fusion (LPBF) of high-temperature alloys such as nickel alloy 718 is one of the key modalities supporting this effort. One of the major drawbacks to LPBF is its slow build speed on the order of 5–10 cubic centimeters per hour print speed. This experimental study investigates how to increase the productivity of the LPBF process by switching from a traditional Gaussian laser shape to a ring laser shape using a nLight multi-modal laser. The objective is to increase productivity, reducing energy consumption and time, without sacrificing mechanical properties by switching to the ring laser thereby improving the sustainability of LPBF. Results include measuring the energy consumption of an Open Additive LPBF system during 718 printing and comparing the microstructure and mechanical properties of the two different lasers. 

Abstract Coke drums are critical units in the delayed coking process to produce lightweight oil products from heavy residual oil. The fulfillment of the designed coke drum lifetime is often obstructed by low-cycle fatigue damage over cyclic thermal and mechanical loading. Considering the tremendous cost of drum replacement and production loss due to shutdown, the coke drum lifetime extension is of great economic significance in the oil and gas industry. A research project regarding coke drum fabrication and repair was initiated in the Manufacturing & Materials Joining Innovation Center (MA2JIC) at the Ohio State University in 2016. The project includes two phases of work. The first phase of the study (2016∼2019) focused on the external weld repair of coke drum materials, while the ongoing second phase of the study (2019∼2023) addressed coke drum fabrication and repair. A novel low-cycle fatigue testing approach was developed using Gleeble thermo-mechanical simulator and was applied to evaluating the performance of coke drum base materials and welded joints under cyclic deformation. The project goal is to improve the fundamental understanding of materials and joint performance that allows the optimization of coke drum design, fabrication, and repair. In this technical paper, the key methodologies and achievements of the project will be introduced, and some future work will be proposed for the next step.