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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. 

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. 

Abstract Temper bead (TB) welding is often used as an alternative to post weld heat treatment (PWHT) for repair of pressure vessels and piping in the nuclear power industry. Historically, qualification of TB welding procedures has employed the Charpy V-notch test to ensure acceptable heat-affected-zone (HAZ) impact properties. The 2004 Edition of ASME Section IX provided a new provision in QW-290 that allows temper bead qualification using a peak hardness criterion. The peak hardness provision is appropriate for industries such as oil and gas, where peak allowable hardness is specified to ensure adequate resistance to sulfide stress cracking in sour service environments. However, a peak hardness criterion is not appropriate where impact properties are specified for resistance to brittle fracture during low temperature conditions that can occur during certain postulated accident scenarios at a nuclear power plant. Work at the Electric Power Research Institute (EPRI) and The Ohio State University (OSU) show that a hardness drop protocol can be used to demonstrate acceptable impact properties in the HAZ of a temper bead weld. This paper presents a quantitative correlation between hardness measurements and HAZ microstructures with presumed optimum impact properties using a hardness drop approach. The overarching goal is to develop a hardness test protocol for temper bead weld procedure qualification for applications where impact properties are specified. 

This study evaluates how heat input influences an in-situ interlayer hot-forging strategy applied to wire-arc directed energy deposition (DED) of 316L stainless steel. By integrating a compact pneumatic hammer with a controlled short-circuit GMAW-based DED system, the process enables high-temperature deformation capable of refining the solidification microstructure during layer-by-layer fabrication. Using a reciprocating-wire short-circuit GMAW process, changes in wire-feed speed produced distinct heat-input levels that significantly affected the thermal profile, weld bead shape, and the in-situ forging. Electron backscatter diffraction (EBSD) revealed a transformation from coarse columnar grains (158.6 µm) with strong < 100 > {200} texture in the non-forged condition to fine equiaxed grains (~ 45 µm) with reduced texture intensity in the deformed deposits, most pronounced at lower heat input. In the hot-forged samples, the storage strain energy increased, reflected by higher Kernel Average Misorientation (KAM) values and broader distribution compared to the conventional condition. Hot forging also increased microhardness, reaching up to 264 HV compared to 175 HV in conventional wire-arc DED. These findings demonstrate that in-situ forging at high temperatures is a promising method to enhance the microstructure and mechanical performance of wire-arc DED components, although geometric distortion and increased surface roughness remain important considerations for future process optimization. 

The growing use of duplex stainless steels (DSSs) has spurred extensive research and development, particularly concerning weldability challenges. The increasing interest in additive manufacturing (AM) using directed energy deposition (DED) has further highlighted the need for precise sample preparation to ensure accurate microstructural characterization. This paper consolidates best practices for preparing samples to effectively reveal microstructures and secondary phases in DSSs. By optimizing polishing techniques and etching methods, the work provides guidelines for distinguishing ferrite and austenite across the base material, heat-affected zone (HAZ), and weld metal, while also enabling the detection of intermetallic phases and discrete secondary precipitates. Examples of typical deviations, etching phenomena, and potential pitfalls are also provided. The preparation strategies presented are tailored to support subsequent analysis using light optical microscopy (LOM), scanning electron microscopy (SEM), electron backscatter diffraction (EBSD), and transmission electron microscopy (TEM). 

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. 

A recent collaboration led by NASA Marshall Space Flight Center and OSU is pioneering experiments and talent development to push boundaries for in-space manufacturing 

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. 

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.