This study investigates the impact of build platform location on melt pool variability during laser-based powder bed fusion of metals. The incident angle and gas flow are hypothesized to influence melt pool penetration and contribute to spatial variations in the melt pool. Results show that the typical build strategy using the same material-dependent processing parameters for all parts throughout the build chamber produces parts with location-dependent properties. An overarching goal of the present work was to attempt to fabricate similar parts at different locations within the build chamber by identifying processing parameters that produce similar melt pool depths at these locations. It was further hypothesized that by normalizing process parameters through similar melt pool depths, similar porosity counts could be achieved at these locations, thus mitigating process-induced variability. The study emphasizes the necessity of spatial parameter adjustments to minimize variability across different locations within the build platform, as well as the requirement for uniform gas flow across the build chamber, thereby eliminating gas flow-dependent variations from the analysis.

Installation qualification for laser-based powder bed fusion of metals (PBF-LB/M) machines is challenging due to the extensive labor, time, and financial costs required by current standards. These standards demand long builds, expensive equipment, and specialized expertise, primarily focusing on mechanical properties, which complicates the analysis of subsystem performance where attention may be required. Consequently, this makes machine installation qualification both inaccessible and inconsistent for typical PBF-LB/M users. This study presents a new methodology for installation qualification of PBF-LB/M scanner subsystem hardware and control software that addresses these challenges, empowering users to qualify their systems. A plate melt setup using a commercially available 25.4-millimeter square stainless-steel plate was designed to characterize scanner performance through a series of “pass” or “attention required” tests assessing laser and scanner delays, scanner acceleration, dimensional accuracy, and slicer file software interpretation. The method was then applied on four PBF-LB/M machines, with one plate scanned per laser under machine original equipment manufacturer (OEM) recommended build conditions. Laser power and scan speed parameters were specified to be the same for the four machines. The results show notable variations in scanner delays, scanner momentum control, and path planning file preparation that impact the results of the laser welding. A simple example of the machine-to-machine variability was captured when three out of the four machines tested were unable to produce dimensionally accurate 1 mm diameter circles. In addition, all machines required attention during numerous tests aimed at slicer file software interpretation, which highlights critical gaps in the physical and programmable scanner control of PBF-LB/M machines. Overall, this study demonstrates the potential of the proposed plate melt method to assess scanner subsystem performance without the challenges of current standards.

In laser-based powder bed fusion of metals (PBF-LB/M), variations in laser scanner movements, particularly lesser-studied parameters like scanner delays that control laser directional changes, can influence the microstructure in a part during fabrication as each of typically millions of individual laser vectors impact part thermal history and resulting microstructure. While the impact of commonly researched parameters such as laser power, scan speed, hatch spacing, and layer thickness on part microstructure have been well studied, considerably less attention has been given to scanner delays such as the polygon delay. This study uses electron backscatter diffraction to investigate the microstructural variations caused by polygon delay values ranging from 0 to 450 microseconds, beginning with individual scan tracks. The study then extends single tracks to a simple three-dimensional part to examine if microstructure differences due to polygon delays may be influenced by localized heating and cooling caused by nearby hatch vectors and successive layers. The results reveal that varying polygon delay clearly affects grain morphology during individual scan tracks, although these effects are less clear during a three-dimensional build. Future PBF-LB/M studies should focus more on understanding time-resolved laser beam processing effects to better reduce inconsistencies and improve part quality.

Laser powder directed energy deposition (LP-DED) additive manufacturing (AM) deposited Inconel 718 claddings (at laser power levels of 800, 1000, and 1200 W) onto Inconel 625 substrates fabricated by electron beam powder-bed fusion (EB-PBF). The cladding components were post-process heat treated for 1 h at temperatures of 1025 °C, 1175 °C, and 1250 °C. The microstructures and Vickers hardnesses were examined and compared for the as-built and heat treated cladding components. As-built claddings consisted of columnar dendrites and precipitate columns while the heat-treated microstructures consisted of varying degrees of recrystallization and grains containing {111} fcc annealing twins. The as-built cladding bond consisted of a 25 - 50 μm wide transition zone while the heat treated cladding bonds consisted primarily of linked grain boundaries sometimes alternating between the Inconel 718 alloy cladding and the Inconel 625 substrate. For the as-built components, the hardness increased from the Inconel 625 substrate to the Inconel 718 cladding. For the heat treated components, the hardness for the Inconel 718 cladding was lessened with increasing heat treatment temperature, but was overall similar to the Inconel 625 substrate.

Shielding gas flow in metal Laser Powder Bed Fusion (PBF-LB/M) removes ejecta and byproducts from the build plate and the optical path, preventing laser interference and loss of part quality. Previous research conducted on an EOS M290 used Magnetic Resonance Velocimetry (MRV) to resolve the three-component, three-dimensional flow field and identified a region of recirculation below the lower vent. The present work demonstrates the correction of this recirculation through practical chamber modifications: raising the build platform and optical assembly, and redesigning the recoater and the lower inlet to reflect the new build plate position. MRV was leveraged to generate flow distribution maps and velocity profiles of the modified configuration, showing a marked change in the overall flow field. Plate scans across the build area characterized the impact of gas flow improvements on process response. Specimens from the original configuration showed progressively shallower melt pools toward the vent, whereas those from the modified configuration exhibited a ~10% higher average melt pool depth in the region most affected by prior recirculation. Qualification artifacts built under both conditions provided preliminary evidence of improved part performance via enhanced gas flow distribution. These results highlight potential benefits of uniform gas flow distribution across the build plate through simple EOS M290 chamber modifications.

Additive manufacturing (AM) creates three-dimensional objects using various approaches, typically layer-by-layer. One emerging method is laser-based powder bed fusion of metals (PBF-LB/M), which uses high-energy lasers to melt metallic powder into shape. AM processes are influenced by many factors, yet there is no standardized framework for quantifying their effects on final products. This guide introduces key principles of experimental design and statistics, outlining a roadmap for conducting rigorous experiments. We review the literature on AM generally and PBF-LB/M specifically to assess how well current practices align with standardized methodologies. In addition, we compare the evolution of experimental techniques in PBF-LB/M to those in a more regulated industry to explore potential cross-pollination. Our analysis reveals that most studies do not adhere to best practices in experimental design and statistical analysis. For example, randomization of run order is rarely mentioned, and statistical model assumptions are often unchecked. Even in tightly regulated fields, experimental designs and statistical methods remain basic and lack sophistication. To improve research quality, we provide recommendations for establishing standardized experimental and reporting practices in AM.

The Laser-based Powder Bed Fusion of Metals (PBF-LB/M) process has shown potential in the manufacturing of critical flight components, yet also has faced difficulties in achieving reproducibility. One potential reason for this is that tensile testing, which is one of the methods traditionally used to ascertain quality in the additive manufacturing (AM) industry, is insufficient for capturing underlying flaws in an additively manufactured component. To quantify the ability of tensile testing to detect underlying flaws in a component, a generalized full factorial experiment was performed where the tensile properties of UNS N07718 were measured across several types of build conditions. Combinations of differently sized bars and surface conditions were investigated. Defects were induced by amplifying the polygon delay parameter, hence prolonging the dwell time of the laser in the contours. The authors found that those tensile bars that experienced increased polygon delay had similar to 10x more pores than those built with nominal parameter values while still maintaining an average porosity of <0.25 % (i. e., a total part porosity that is acceptable by NASA-STD-6030). Regardless of the specimen geometry and surface condition, differences between parts which had undergone polygon delay and those that had not were either statistically insignificant or were too small to be relevant, indicating that tensile testing may not be an effective metric for identifying the quality of a PBF-LB/M process.

This study investigates a series of geometric feature build plates manufactured by multiple laser powder bed fusion (L-PBF) machine configurations, examining seven different wall thicknesses ranging from 0.1 to 2.0 mm. These build plates and thin wall specimens completed a full heat treatment cycle: stress relief (SR), HIP, solution, and aging per standards. The fully heat-treated (FHT) Inconel 718 wall specimens were sectioned from sixteen different geometric feature build plates built across fifteen different L-PBF machines. They were characterized by optical microscopy and EBSD image mapping. The microstructural evolution from the As-built sample, SR, HIP to FHT wall specimens from a single machine configuration was also obtained along with cooling rate simulations for 0.1 mm, 0.2 mm, 0.5 mm, and 0.8 mm wall thicknesses. The difference in cooling rates between the thick and thin walls was simulated to provide an understanding of microstructural evolution and evaluate the computer simulation as a tool to predict microstructural features. For FHT wall specimens, results indicate mostly equiaxed grain structures containing annealing twins, ranging in size from ∼ 21 microns to 93 microns parallel and perpendicular to the build direction. For most of the samples, the grain size was shown to increase with the increasing wall thickness due to slower solidification rates. The double aging composing the fully heat-treated thin walls also fully age-hardened the grain structures with gamma double-prime precipitates. This precipitation produced a median Vickers (HV) hardness for nominal section thicknesses > 0.6 mm of ∼ HV 472; consistent with commercially heat-treated and optimized Inconel 718 products. Feature sizes > 0.6 mm were reproducible for all L-PBF machine configurations.

The fatigue performance of laser powder bed fusion-fabricated Ti-6Al-4V alloy was investigated using four-point bending testing. Specifically, the effects of keyhole and lack-of-fusion porosities along with various surface roughness parameters, were evaluated in the context of pore circularity and size using 2D optical metallography. Surface roughness of Sa = 15 to 7 microns was examined by SEM, and the corresponding fatigue performance was found to vary by 102 cycles to failure. The S-N curves for the various defects were also correlated with process window examination in laser beam power-velocity (P-V) space. Basquin's stress-life relation was well fitted to the experimental S-N curves for various process parameters except keyhole porosity, indicating reduced importance for LPBF-fabricated Ti-6Al-4V alloy components.

In this study, a holistic evaluation strategy employing a complex test artifact, coupled with single line scan tracks, was employed to examine the influence of different laser beam energy profiles on various features of laser-based powder bed fusion of metals (PBF-LB/M). Using IN718, results revealed a significant influence of the laser beam on bead geometry. Specifically, the conventional Gaussian beam produced deeper, concave-shaped melt pools, while the ring beam resulted in wider and shallower beads. In terms of productivity, the artifacts (two each) fabricated using the Gaussian beam required 6 h and 6 min of build time, while those built using ring beam required only 3 h and 49 min (37% build time reduction) but a defocused Gaussian beam (not included in this study) can match the productivity of the ring beam. However, the holistic approach using the complex test artifact highlighted drawbacks associated with the ring beam, including increased lack of fusion porosity, compromised resolution for features below 0.5 mm, and less than 10% elongation to break in both as built and heat-treated conditions. While acknowledging the potential for improvement through further process optimization, the study concludes that the shallower melt pools produced by the ring beam may cause limitations as layer thicknesses increase. Microstructural analysis revealed distinct grain characteristics, with the Gaussian beam producing more equiaxed grains and the ring beam favouring columnar grains positioned along the build direction. The work primarily highlights the need for and benefits from a holistic analysis in PBF-LB/M technology, ensuring data driven outcomes.

Current thermal monitoring methods used in metal powder bed fusion (PBF) additive manufacturing (AM) rely on a priori knowledge of the emissivity, which is usually assumed temperature, wavelength, and time invariant. Given the true dynamic nature of emissivity for a given material, these assumptions result in the calculation of inaccurate process temperatures, or in the reporting of radiant intensity or radiance temperature as a proxy for the absolute temperature. In this work, we detail the use of a multi-wavelength (MW) pyrometry technique, operating in the spectral range from approximately 900-1700 nm, to capture radiant intensity emissions during processing of various materials using the electron-beam powder bed fusion (PBF-EB) process. The technique measured spectral intensity and analyzed the results of these data after processing with Planck's distribution law in its two-color or ratio pyrometry form to establish the spectral and temporal emissive behavior in the active range from 1080-1637 nm. Four commonly used alloys (Ti6Al4V, TiAl, 316 L, and IN625) were examined here as each of these alloys underwent transitions (from powder to liquid to structured solid) induced during processing. For each material studied, analysis of the aggregated data for ten layers, superimposed in time, identified specific and repeatable trends in the emissivity, with plotted measurements forming clusters or regions in each of the processing stages (preheating, melt scanning, liquid, and cooldown). Also, the data recorded by the MW pyrometer was used to analyze the spectral variability of measurements as well as temporal changes in emissive behavior (from gray to non-gray) at similar temperatures and points in time in each processing stage but during different layers or scans. The results show that the measured emissive behaviors for the four materials were highly variable during processing, with typical differences during transitions ranging from 20% to 75%, and as high as 300% for the case of Ti6Al4V, indicating emissive behaviors that are highly dynamic rather than temporally and spectrally invariant. This dynamic emissive behavior is associated with changes in temperature, morphology, phase, and chemistry of the processed metal that happen during the highly transient and nonequilibrium conditions of PBF AM, and that can only be accounted for by performing in situ measurements during processing using techniques that do not rely on prior knowledge of the emissivity. These results are intended to (1) better inform the additive manufacturing community on the physical nature of emissivity of metallic materials during processing, and (2) provide foundational emissivity data that can be used to improve numerical modeling and the application of radiation thermometry techniques in PBF AM. Further, these results indicate that the emissive behavior during processing can result in significant variations temporally and spectrally, and although the results can be used as foundational emissive behavior measurements, the authors recommend the use of in situ techniques that operate without prior knowledge of emissivity to reduce uncertainties in measurements during PBF AM.

Inconel 718 is a widely popular aerospace superalloy known for its high-temperature performance and resistance to oxidation, creep, and corrosion. Traditional manufacturing methods, like casting and powder metallurgy, face challenges with intricate shapes that can result in porosity and uniformity issues. On the other hand, Additive Manufacturing (AM) techniques such as Powder Bed Fusion (PBF) and Direct Energy Deposition (DED) can allow the creation of intricate single-part components to reduce weight and maintain structural integrity. However, AM parts often exhibit directional solidification, leading to anisotropic properties and potential crack propagation sites. To address this, post-processing treatments like HIP and heat treatment are necessary. This study explores the effects of the raster and stochastic spot melt scanning strategies on the microstructural and mechanical properties of IN718 parts fabricated using Electron Beam Powder Bed Fusion (EB-PBF). This research demonstrates that raster scanning produces columnar grains with higher mean aspect ratios. Stochastic spot melt scanning facilitates the formation of equiaxed grains, which enhances microstructural refinement and lowers anisotropy. The highest microstructural values were recorded in the raster-produced columnar grain structure. Conversely, the stochastic melt-produced transition from columnar to equiaxed grain structure demonstrated increased hardness with decreasing grain size; however, the hardness of the smallest equiaxed grain structure was slightly less than that of the columnar grain structure. These findings underscore the vital importance of scanning strategies in optimizing the EB-PBF process to enhance material properties.

Freedom of design is a major tenant of additive manufacturing (AM); however, this necessitates the evaluation of advanced measurement systems for comprehensive part evaluation to ensure production of geometries as intended. This research analyzed contact [Coordinate measuring machine (CMM) and Caliper] and non-contact [Optical and X-ray computed tomography (XCT)] measurement systems on as built and surface finished qualification test artifacts (QTA), from the Global Test Artifact Data Exchange Program, fabricated in Ti-6Al-4 V using a laser powder-based fusion (LPBF) system. The CMM measurements were performed at a certified laboratory, while the other measurements were taken at the W. M. Keck Center for 3D Innovation at UTEP using standard operating procedures for applicable systems. The use of Calipers measurement methods is recommended for general beam compensation and scaling factor adjustments. Measurement differences when calculating beam compensation from the benchmark method (CMM) and (Caliper) was 0.020 mm and the difference between CMM and the Optical method was 0.010 mm, when analyzing the surface finished artifact. Highly accurate methods, such as CMM, are recommended for individual feature adjustments and only when the manufacturing process and post process tolerances capabilities are less than 0.020 mm which in case of LPBF systems is not achievable. For GD T characteristics, the differences between CMM and XCT measurements were similar (0.050 mm) across the reported zones for tolerances, within a surface roughness range of Sa = 0.004–0.011 mm. This indicates that the contributing factors to measurement variations are not only related to surface roughness but also include the configurations of the measurement systems. These configurations encompass the definition of edges or faces, the location and size of the measured features, and the type of feature being evaluated.

The present study investigated the effects of Hot Isostatic Pressing (HIP) on the fatigue performance of Laser Powder Bed Fusion (L-PBF) Ti-6Al-4V alloy under both 4-point bending and uniaxial testing. Three HIP-cycles were examined: standard, low temperature/high pressure (LTHP), and super beta. Moreover, an annealed heat treatment group was incorporated to compare against the HIP groups. The material microstructure was analyzed and compared across the heat treatments during the study, which showed the presence of α' martensites, α+β Widmanstätten, and coarse equiaxed grains. Similarly, tensile and hardness testing were implemented to study the mechanical properties, where due to the effects of the HIP treatments, higher ductility but lower hardness values were recorded. Furthermore, fracture morphologies and stress-life (cycles-to-failure) (S-N) curves of the Ti-6Al-4V specimens concerning the fatigue behavior were analyzed. The HIP treatment groups behaved similarly during 4-point bending and uniaxial testing, with the LTHP obtaining a superior fatigue life behavior, followed by the standard and super beta HIP groups. In addition, the efficacy of HIP to reduce pores showed better results in the 4-point bending specimens, leading to few defects as fatigue initiators in contrast to the uniaxial specimens. Fractography results suggested that defects and microstructural features acting as fatigue crack initiators (FCI) govern the fracture behavior of uniaxial specimens. In contrast, only the presence of microstructural features controls the 4-point bending failure behavior.

AlSi7Mg (F357) alloy specimens were fabricated in two different laser powder bed fusion (LPBF) systems: EOS M290 and SLM 280HL. Vertical (Z) and horizontal (XY) orientations were fabricated, and five different thermal post processes were applied to samples, individually. According to ASTM F3318-18, the considered thermal conditions were as-built, stress relieved (SR1), HIP, T6 and HIP+T6. Subsequently, the individual samples were aged at 140 °C and 177 °C for 100 h and for up to 1000 h. Tensile specimens were machined down from the aged samples and tested as per ASTM E8/E8M-21. While the yield stress (YS), elongation (%), and Vickers microindentation hardness (HV) were somewhat different for the as-built components, the general trends for the different heat treatments were essentially the same. As-built and SR1 treated microstructures were dominated by microdendritic cells, while the HIP, T6 and T6 + HIP component microstructures consisted of recrystallized grains containing eutectic Si particles of various sizes and shapes within the grain interiors and the grain boundaries; which gave rise to wide-ranging mechanical properties. As an example of these widely-ranging mechanical properties, it was observed that components fabricated in the Z or build direction in the EOS system exhibited a YS, elongation, and HV of 225 MPa, 13%, and HV120, while when HIPed and unaged exhibited values of 87 MPa, 25%, and HV51, respectively. These same HIPed components when aged at 177 °C for 1000 h exhibited values of 81 MPa, 41% and HV44. The mechanical properties of the unaged, HIPed and aged fabricated in Z direction in SLM system were 85 MPa, 31%, HV51, and 80 MPa, 42%, and HV47, respectively, providing support for LPBF system fabrication compatibility. These measured mechanical property values represent a small fraction of the more than 1600 mechanical property measurements (YS, UTS, elongation, and hardness (HV)) in this study.

We present a new computational approach for large-scale segmentation and spatially-resolved analysis of melt pools in complex 3D printed parts and qualification artifacts. Our hybrid segmentation includes human-in-the-loop image processing of a few representative optical images of melt pools that are then used for training machine learning models for automated segmentation of melt pool boundaries in large parts. Our approach specifically targets minimizing the need for manual annotation. Considering imperfect segmentation and errors unavoidable with most algorithms, we further propose chord length distribution as a statistical description of melt pool sizes relatively tolerant to segmentation errors. We first show and validate our new approach on optical images of melt pools in a simple 3D printed plate sample (IN718 alloy) as well as selected regions of a complex qualification artifact (AlSi10Mg alloy). We then demonstrate the application of our approach on an entire cross section of the artifact.

Radiation thermometry techniques have been implemented to measure thermal signatures in powder bed fusion (PBF) additive manufacturing (AM), including the use of imaging devices with a large field of view, to measure large areas of the powder bed with spatial discrimination, and those considered single spot devices that measure signatures from a small region. Traditionally, these techniques can be categorized as single-color (brightness) or two-color (ratio) pyrometry; imaging devices are single-color while spot devices can be either. Both techniques can be used to infer a target temperature using a priori knowledge of the emissivity or employing the graybody assumption of constant emissivity across the spectrum. However, the dynamics of PBF AM, where a concentrated heat source is employed to selectively melt powder material, lead to complex material phase transitions under non-equilibrium solidification conditions. This makes it challenging to measure accurate thermal signatures because the emissivity of the target is also constantly varying as the PBF process unfolds. In this work, we employed an established technique of multi-wavelength pyrometry in an electron beam powder bed fusion (PBF-EB) system to continuously measure temperatures and the thermal emissive behavior during sintering and melting of an Inconel 625 powder that was subjected to preheating by direct scanning with the electron beam. The measurements displayed distinctive changes in signal strength or emissivity (in the wavelength range between 1080 nm and 1640 nm) that indicated the material phase change from loose to sintered powder to molten material and finally to solidified material; these changes in signal strength/emissivity were correlated with electron microscopy observations. This work highlights the suitability of multi-wavelength (MW) pyrometry as an in situ diagnostic tool to identify thermal process signatures (i.e., absolute temperatures), and the radiative emissive behavior of the materials being processed. Several demonstrations of the use of this MW pyrometry technique as a diagnostic tool are provided, illustrating its ability to sense signal strength/emissivity differences as the material experiences changes due to its temperature, phase, morphology, and chemistry. Although spatial and temporal improvements in the technique can be pursued, the sensitivity of the approach is demonstrated, as an example, in the ability to capture the passing thermal wavefronts arising from the scanning electron beam. It is anticipated that this technique and the information it provides can be leveraged in the development of advanced techniques for thermal monitoring and process control in PBF.

The aim of this manuscript is to give a compact overview of the results that illustrate the applicability of processing-structure-property relationships in the increasingly important context of 3D printing of metals. A process qualification approach based on the physics-based understanding of defect formation in laser powder bed fusion (L-PBF) additive manufacturing (AM) is investigated for an aerospace-grade titanium alloy (Ti-6Al-4V). A physically interpretable qualification approach is critical for enabling L-PBF part certification for structure-critical applications. This approach relies on systematic experimentation, characterization, testing, and data analysis tasks including design of experiments varying power and velocity to generate varying defect populations, process window development based on defect structure, high throughput fatigue testing, and fractography, 2D porosity characterization, and use of extreme value statistics to develop a porosity metric that, in turn, could have predictive power for the variation in fatigue performance. Results from four-point bend fatigue tests demonstrate that a process window can be defined based on this key mechanical property. This relatively high throughput approach can, in turn, support a reduced set of round bar fatigue tests typically used for qualification. Overall, the proposed ecosystem for process qualification of L-PBF AM shows promise and is expected to apply to other materials and powder bed fusion AM technologies.

In laser-based powder bed fusion of metals (PBF-LB/M) systems, the shielding gas flow is important for controlling the accumulation of melting byproducts such as soot and ejecta near the melt pool as well as sweeping ejecta, agglomerates, and “flying” powder away from the build region. It is necessary to understand the flow field throughout the build chamber in order to sufficiently control these contaminants to prevent their interference with delivered laser power and maintain part quality. A measurement technique called Magnetic Resonance Velocimetry (MRV) was applied to measure the entire three-dimensional three-component mean velocity field in a scaled flow model of a commercial EOS M290 PBF-LB/M build chamber. Flow conditions in the model were at a Reynolds number of 36000 (based on the average bulk velocity in the supply duct and its diameter) comparable to conditions in the full size M290. MRV measurements reveal five large jets issuing from the upper vent of the M290: the top jet supplies fresh gas flow across the optics keeping them clean, three jets issue horizontally, and the last jet travels downward impinging on the center of the build plate potentially sweeping contaminants toward the exit or delivering contaminants to the surface from the upper portion of the chamber. The lower vent supplies flow across the build plate, but this flow issues from above the build plate creating a backward facing step flow in which a region of separation with backwards flow exists. The backwards flow extends several centimeters over the edge of the build plate nearest to the vent before the inlet flow “attaches” to the build plate and proceeds to the exit. Single layer laser scans on individual titanium plates spaced uniformly around the build surface are performed, and their melt pool depths are measured as an indication of delivered laser power. Measured depths for plates in the separated flow region are measured to be 23 % shallower than in the central region of the build plate where the flow is unidirectional toward the exit. The influence of the shielding gas flow on melt pool depth is demonstrated using an extra vent placed below the lower vent to supply unidirectional flow across the build plate in the separated flow region. With the flow improvement, the melt pool depths increased by 15 %. These experiments support arguments that shielding gas flow is important for building consistent high quality parts and demonstrate the utility of MRV measurements for investigating, understanding, and potentially improving the shielding gas flows in PBF-LB/M systems.

This study examines and compares the microstructures, Vickers microindentation hardness, and mechanical properties for additively manufactured (AM) samples built by a variety of AM processes: wire arc AM (WAAM), electron beam powder bed fusion (EB-PBF), laser wire direct energy deposition (LW-DED), electron beam direct energy deposition (EB-DED), laser-powered direct energy deposition (LP-DED), and laser powder bed fusion (L-PBF). These AM process samples were post-processed and heat-treated by stress relief annealing at 1066 °C, HIP at 1163 °C, and solution annealing treatment at 1177 °C. The resulting microstructures and corresponding microindentation hardnesses were examined and compared with the as-built AM process microstructures and hardnesses. Fully heat-treated AM process samples were mechanically tested to obtain tensile properties and were also evaluated and compared. Principal findings in this study were that high-temperature heat treatment >1100 °C of AM process-built samples was dominant and exhibited recrystallized, equiaxed grains containing fcc {111} annealing twins and second phase particles independent of the AM process, in contrast to as-built columnar/dendritic structures. The corresponding yield stress values ranged from 285 MPa to 371 MPa, and elongations ranged from 52% to 70%, respectively. Vickers microindentation hardnesses (HV) over this range of heat-treated samples varied from HV 190 to HV 220, in contrast to the as-built samples, which varied from HV 191 to HV 304.