Powder-bed Process Research Articles

Localized Laser Heat Treatment on AISI 1045 Steel Using a LPBF Laser

ABSTRACTLaser heat treatment (LHT) can provide local microstructure modification for metallic materials. This study investigates the viability of LHT on AISI 1045 steel using a laser designed for laser powder bed processing (LPBF) with a very small beam diameter compared to existing literature. Energy density models from the literature are analyzed and adapted to improve consistency across varying laser properties, mainly focusing on spot size and laser–material interaction time. Fifteen different laser parameter schematics are evaluated, comparing hardness versus depth relations as well as laser‐affected zone (LAZ) profiles. Through adapting the energy density model, new laser parameters are calculated and demonstrated to produce a valid localized heat treatment.

Review of the Use of Metals in Biomedical Applications: Biocompatibility, Additive Manufacturing Technologies, and Standards and Regulations

Advanced manufacturing techniques such as Additive Manufacturing (AM) have grown rapidly in major industries such as aerospace, automotive, and biomedical device manufacturing. Biomedical industry has benefitted immensely from AM because of its flexibility in design and its rapid production cycle. Powder bed processes are the major production technique for metal-based AM implants. This paper serves as a comprehensive review on the research efforts being made using AM to develop new patient centered medical devices. This review focuses on AM of the most common metals for biomedical applications, Magnesium alloys, Cobalt-Chromium alloys, pure Titanium, Titanium alloys. Several different aspects are discussed including biocompatibility and osseointegration, application of specific metals in different types of implants, their advantages and disadvantages, mechanical properties in comparison to bone, and their production technologies. Regulatory and quality assurance hurdles that are facing new innovations made using AM are discussed.

Heat Treatment Post-Processing for the Improved Mechanical Properties of Scalmalloy® Processed via Directed Energy Deposition

As high-strength aluminum alloys present several processability issues with additive manufacturing (AM), Scalmalloy®, an Al-Mg-Sc-Zr-based alloy, has been developed. This alloy is age-hardenable, allowing it to precipitate out a strengthening precipitate phase, Al3(Sc,Zr). The manufacturer recommends a single-stage aging treatment at 325 °C for 4 h; however, the majority of the literature studies utilize a powder bed processing known as selective laser melting (SLM) over powder-fed processing directed energy deposition (DED). This study addresses the lack of information on heat treatments for DED fabrication by exploring the application of artificial aging temperatures of 300–400 °C for 2, 4, and 6 h to: 1. determine the impact on the microstructural evolution and mechanical performance and 2. determine whether the recommended treatment for Scalmalloy® is appropriate for DED fabrication. Tensile testing determined that low-temperature treatments exhibited no visible dependence on time (2–6 h); however, time becomes influential at higher temperatures starting at 350 °C. The temperature plays a considerable role in the mechanical and microstructural behaviors of DED Scalmalloy®. The highest tensile strength was noted at 300 °C (384 MPa, 21.6% increase), but all heat-treated cases resulted in an improvement over the as-built case. This investigation established that increasing the treatment temperature resulted in a decreasing trend for the tensile strength that held over time. Elongation at 2 h displayed a near parabolic trend that peaks at 350 °C (20%) and falls with higher temperatures. At the 4 h treatment, a slight decreasing trend was noticed for elongation. No visible change was observed for elongation at 6 h, with elongation values remaining fairly consistent. The microstructural evolution, including micron-sized and nano-sized Al3(Sc,Zr) and grain size, was examined, and coarsening effects were noted with the increase in the temperature. It is recommended that treatment be conducted at 300 °C to achieve the precipitation of the strengthening Al3(Sc,Zr) phase while minimizing coarsening.

Dimensional Accuracy and Mechanical Characterization of Inconel 625 Components in Atomic Diffusion Additive Manufacturing

Metal material additive manufacturing (MEAM) has risen in interest in the last five years as an alternative to powder bed processes. MEAM is promising for generating shelled components with defined infill structures, making it very interesting for lightweight engineering. Atomic Diffusion Additive Manufacturing (ADAM) is a filament-based MEAM process patented by Markforged Inc. that provides a closed process chain from preprocessing to the final sintering of printed green parts. This study focuses on Inconel 625, which is of high interest in the aerospace industry, and assesses its dimensional accuracy and tensile properties regarding different print orientations and solid, triangular, and gyroid infill structures. The results showed that neither the dimensional accuracy nor the sintering shrinkage was significantly influenced by the printing orientation or the infill structure. In the context of lightweight engineering, the infill structures proved beneficial, especially within the elastic region. Generally, triangular infill patterns resulted in higher stiffness, while gyroids led to more ductile specimens. A mass-related evaluation of tensile testing elucidates that with the aid of the infill structures, weight savings of 40% resulted in mechanical performance decreasing by only 20% on average, proving its high potential for lightweight design.

Layer-to-layer closed-loop feedback control application for inter-layer temperature stabilization in laser powder bed fusion

In laser powder bed fusion (LPBF), part quality and process conditions are highly dependent on the interlayer temperature (ILT) of the exposure surface of printed parts. State-of-the-art closed-loop control applications do not stabilize ILT, which has a decisive influence on the resulting part properties. This paper presents a closed-loop control strategy for LPBF that stabilizes the ILT. The thermal balance is defined with respect to exposure area change in overhanging parts and a control strategy is proposed to maintain the thermal balance by actuating energy input. The proposed control strategy uses an off-axis thermal camera for interlayer temperature acquisition to update the laser power layer to layer. An online optimization-based controller that leverages the repetitive nature of the LPBF process is implemented for the task. The developed controller is validated by experiments with different overhanging geometries. Successful ILT stabilization for various overhanging angles shows the robustness of the controller for an extended number of layers. However, modulation of laser power alone is shown to be insufficient to maintain the ILT within the stable processing window due to excessive heat accumulation in the long term. Nevertheless, the results of this study demonstrate the feasibility of ILT stabilization via of closed-loop control in LPBF and the potential for significant improvements in stabilizing the properties of the printed parts.

Surface Properties and Tribological Behavior of Additively Manufactured Components: A Systematic Review

Innovative additive manufacturing processes for resilient and sustainable production will become even more important in the upcoming years. Due to the targeted and flexible use of materials, additive manufacturing allows for conserving resources and lightweight design enabling energy-efficient systems. While additive manufacturing processes were used in the past several decades mainly for high-priced individualized components and prototypes, the focus is now increasingly shifting to near-net-shape series production and the production of spare parts, whereby surface properties and the tribological behavior of the manufactured parts is becoming more and more important. Therefore, the present review provides a comprehensive overview of research in tribology to date in the field of additively manufactured components. Basic research still remains the main focus of the analyzed 165 papers. However, due to the potential of additive manufacturing processes in the area of individualized components, a certain trend toward medical technology applications can be identified for the moment. Regarding materials, the focus of previous studies has been on metals, with stainless steel and titanium alloys being the most frequently investigated materials. On the processing side, powder bed processes are mainly used. Based on the present literature research, the expected future trends in the field of tribology of additively manufactured components can be identified. In addition to further basic research, these include, above all, aspects of process optimization, function integration, coating, and post-treatment of the surfaces.

Influence mechanism of laser delay on internal defect and surface quality in stitching region of 316L stainless steel fabricated by dual-laser selective laser melting

Multi-laser stitching additive manufacturing technology is an effective solution to break through the size limitation in single-laser additive manufacturing based on a powder-bed process, where excellent metallurgical bonding and high surface quality of the multi-laser stitching region (overlap) are the critical issues to ensure the final forming quality. The above metallurgical bonding and surface quality are not only affected by common process parameters but also sensitive to laser delay (including on and off delay) parameters because they influenced the starting and end regions of melt tracks. In this study, the influence of laser delay parameters on the forming quality of a single 316L stainless steel melt track was first investigated, thereby obtaining an optimization range of laser delay parameters. Then, the influence mechanism of laser delay on the internal pore defects and surface quality in the dual-laser stitching region was systematically studied. The results show that with the increase of laser on delay, there are four kinds of internal defects in the stitched region, namely keyhole, irregular pore, large-size continuous pore and non-overlap. In addition, due to the high energy density at the starting/end point of the melt tracks, powder denudation and solidified bulge were observed near the stitching line, which leads to the undulation problem with layer-by-layer accumulation on the surface in the stitching region. It is found that the surface undulation with a height of 202 μm and a width of 723 μm still exists at the optimized laser delay parameters (porosity of 0.96 %), which means new process strategies are also needed to be developed besides optimization of laser on/off delay parameters. In addition, a trade-off should be made between the low porosity and high surface quality due to the different influence trends of laser delay on them. This study provides a theoretical basis and technical support for reducing internal defects and improving surface quality in the stitching region fabricated by multi-laser selective laser melting (SLM).

Increasing productivity of laser powder bed fusion manufactured Hastelloy X through modification of process parameters

One of the factors limiting the use of additive manufacturing, particularly powder bed processes, is their low productivity. An approach to increasing laser powder bed fusion (LPBF) build rate without costly hardware modifications is to alter process parameters. This study evaluates the possibilities to increase build rates through this route without compromising material quality. Equations for productivity are derived based on process parameters and build geometry, and applied on the process window for Hastelloy X in LPBF. It is demonstrated that virtually flaw-free parts can be printed at build rates that differ up to tenfold. To investigate potential variations in the microstructure and performance, Hastelloy X specimens manufactured at varying build rates were characterized. Electron backscattered diffraction (EBSD) analysis revealed that the specimen built at the lowest rate shows strong texture with columnar grains, while the specimen built at the highest rate presents significantly more random orientation and evident melt pool contours with pockets of very fine grains at the bottom. Despite the major differences in microstructure, the tensile properties do not necessarily vary substantially. Thus, the results indicate that the build rate of LPBF Hastelloy X can be significantly varied based on process parameters, still yielding consistent mechanical properties.

SLM-processed MoS2/Mo2S3 nanocomposite for energy conversion/storage applications

MoS2-based nanocomposites have been widely processed by a variety of conventional and 3D printing techniques. In this study, selective laser melting (SLM) has for the first time successfully been employed to tune the crystallographic structure of bulk MoS2 to a 2H/1T phase and to distribute Mo2S3 nanoparticles in-situ in MoS2/Mo2S3 nanocomposites used in electrochemical energy conversion/storage systems (EECSS). The remarkable results promote further research on and elucidate the applicability of laser-based powder bed processing of 2D nanomaterials for a wide range of functional structures within, e.g., EECSS, aerospace, and possibly high-temperature solid-state EECSS even in space.

Benchmarking of 316L Stainless Steel Manufactured by a Hybrid Additive/Subtractive Technology

This research study investigated the hybrid processing of 316L stainless steel using laser powder bed (LPB) processing with high-speed machining in the same build envelope. Benchmarking at four laser powers (160 W, 240 W, 320 W, and 380 W) was undertaken by building additively with machining passes integrated sequentially after every ten deposited layers, followed by the final finishing of select surfaces. The final geometry was inspected against the computer-aided design (CAD) model and showed deviations smaller than 280 µm for the as-built and machined surfaces, which demonstrate the good efficacy of hybrid processing for the net-shape manufacturing of stainless steel products. The arithmetic average roughness values for the printed surfaces, Ra (linear) and Sa (surface), were 11.4 um and 14.9 um, respectively. On the other hand, the vertical and horizontal machined surfaces had considerably lower roughness, with Ra and Sa values ranging between 0.33 µm and 0.70 µm. The 160 W coupon contained layered, interconnected lack of fusion defects which affected the density (7.84 g·cm−3), yield strength (494 MPa), ultimate tensile strength (604 MPa), Young’s modulus (175 GPa), and elongation at break (17.3%). By contrast, at higher laser powers, near-full density was obtained for the 240 W (7.96 g·cm−3), 320 W (7.94 g·cm−3), and 380 W (7.92 g·cm−3) conditions. This, combined with the isolated nature of the small pores, led to the tensile properties surpassing the requirements stipulated in ASTM F3184—16 for 316L stainless steel.

Experimental investigation on the electrical, thermal, and mechanical properties of laser powder bed fused copper alloys

This paper presents a thorough investigation of the material characteristics of laser powder bed fused copper alloys. Three different copper alloys, i.e., pure copper, with phosphorus and zinc acting as the main alloying elements, were investigated. The research started by characterizing the starting copper powders and then identified the best process windows for laser powder bed processing to obtain samples with the highest density. Based on the results of process optimization, the electrical, thermal and mechanical properties, i.e., tensile strength, resistance to indentation, and roughness, were characterized. The experimental data showed a maximum relative density of approximately 91% for both alloyed powders, while that of the pure powder was limited to 84.6%. The presence of pores is considered the main limiting factor that inhibits the electrical conductivity, which is up to 68.4 IACS% for the Zn-added powder, and the resistance to indentation, in which the resistance to indentation of pure copper is half that of the zinc-alloyed powder. The tensile properties experience anisotropy caused by the manufacturing process itself, as highlighted by the X-ray diffraction analysis carried out after the samples were fabricated. The zinc-added powder shows the best tensile properties, reaching a tensile strength of 400 MPa, which is almost twice that of traditional annealed bulk copper (i.e., 210 MPa). Finally, the roughness is still far from that achievable with classical subtractive techniques, with values of approximately 7 μm for the best pure copper specimens.

Negative impact of humidity on the flowability of steel powders

Atmospheric humidity is introduced into powders during handling, transportation, and storage. High moisture content can increase cohesive forces between particles and make it difficult to spread a powder into thin layers in powder bed processes or to fill a mold in processes such as press-and-sinter. Furthermore, water can cause porosity and uptake of oxygen in the final component, damaging its mechanical properties. In this study, a Freeman FT4 powder rheometer was placed inside a climate chamber. Both flowability and shear tests were performed on four steel powders under a range of humidity and temperatures. Basic flowability energy and specific energy were both found to increase significantly with humidity (typically increase by 50% for 80% of relative humidity compared to dry conditions) and were insensitive to temperature change (10–30 °C). Conversely, the behavior of the powders under shear was neither sensitive to relative humidity nor temperature. Measurements of moisture content revealed that finer powders contained more moisture than coarser ones, but the moisture content was not correlated with humidity, probably due to shortcomings with the measurement method. This knowledge can be used to optimize powder processing conditions.

Lack of fusion mitigation in directed energy deposition with laser (DED-L) additive manufacturing through laser remelting

The void level of a component produced by additive manufacturing can be used to predict the mechanical properties and in most cases it is important to develop processing methodologies able to minimize it. Conventional techniques include parameter optimization and the hot isostatic pressing (HIP). However, in the former there is a limit where improvement becomes minimal and the latter, although it is effective for internal voids, is not efficient in the case of voids located near the surface, which are considered critical. This paper describes a study in which laser remelting was used as an alternative to achieve higher densification after processing using directed energy deposition with laser (DED-L). This technique has been investigated for powder bed (PB) processes, but has not been explored for DED. Understanding the behavior of different materials considering the same processing parameters is also relevant and has not been previously addressed. An ytterbium (Yb) fiber laser with a maximum nominal power of 10 kW and wavelength of 1070 nm was used. Iron and Inconel 625 powders were deposited on an SAE 1010 steel substrate to form beads with intentional voids. The DED-L was performed with a power of 450 W, scanning speed of 600 mm/min and powder feed rate of 10 g/min. The laser radiation was applied over the produced surface at three energy levels: 31.5 kJ/m, 38.2 kJ/m and 45 kJ/m. An in-house MATLAB image processing code was developed in order to assess the void percentage. The results indicated that most of the voids originating from the DED-L process were due to lack of fusion between beads and between the deposit and the substrate. For iron, the void percentage after DED-L varied between 5.3% and 7.1%. After remelting, this value reduced to 1.7% applying 45 kJ/m. It was also noted that in all samples the voids that were initially connected to the surface coalesced because of material redistribution. However, a low repeatability was observed. For Inconel, the void percentage after DED-L varied between 4.4% and 7.1%, and reduced to 3.7% applying 31.5 kJ/m. This reduction is not as significant as that observed for iron and also the degree of dispersion was lower for iron. Hence, laser remelting is able to mitigate voids resultant from DED-L and, consequently, achieve better quality due to a lower probability of component failure. Simultaneously, productivity can be enhanced since the equipment required is the same as that used for the deposition. However, new strategies are needed to increase the process robustness and reduce the degree of dispersion.

Numerical simulation and experimental measurement of pressureless sintering of stainless steel part printed by Binder Jetting Additive Manufacturing

Binder Jetting-Metal Additive Manufacturing (BJ-MAM) is a powder bed-based additive manufacturing technology which deposits liquid binder droplets to join powder particles to form complex shaped structures (i.e., green parts). As the printing process is done around room temperature, BJ-MAM is largely immune to the distortion and cracking issues that can be prevalent in melting based powder bed processes. However, a main issue for BJ-MAM is the part shrinkage and distortion during high-temperature sintering. The densification and deformation behaviors during pressureless sintering of green parts printed by BJ-MAM were studied in this paper. Experimentally, cantilever- and bridge-shaped coupons with varying beam lengths were printed using 316L stainless steel powder; these coupons produced different extents of deformation after sintering. Based on the existing modeling approaches in the powder metallurgy literature, a finite element model was developed incorporating an elastic-viscoplastic constitutive equation for computing both uniaxial equivalent creep strain and volumetric swelling strain. Two methods, a viscosity based and a power-law creep based, were further evaluated for calculating the uniaxial equivalent creep strain. Material property data used in the constitutive equation such as viscosity and creep parameters were collected from the literature, critically reviewed, and then inputted into the model. Other salient features of the model included thermal-mechanical property data that were dependent on both relative density and temperature as well as frictional contact between the part surface and the furnace wall under gravitational load. The calculated quantities such as shrinkage, final relative density, and deformed shapes were compared with the respective experimental data across different part geometries.

3D printing of clay paste enhanced by scrap polymer from powder bed processes

PurposePowder bed additive manufacturing processes are widespread due to their many technical and economic advantages. Nevertheless, the disposal of leftover powder poses a problem in terms of process sustainability. The purpose of this paper is to provide an alternative solution to recycle waste PA12 powder from HP multi jet fusion. In particular, the opportunity to use this material as a dispersion in three-dimensional (3D) printed clay is investigated.Design/methodology/approachA commercial fused deposition modelling printer was re-adapted to extrude a viscous paste composed of clay, PA12 and water. Once printed, parts were dried and then put in an oven to melt the polymer fraction. Four compositions with different PA12 concentration were studied. First, the extrudability of the paste was observed by testing different extrusion lengths. Then, the surface porosities were evaluated through microscopical observations of the manufactured parts. Finally, benchmarks with different geometries were digitalised via 3D scanning to analyse the dimensional alterations arising at each stage of the process.FindingsOverall, the feasibility of the process is demonstrated. Extrusion tests revealed that the composition of the paste has a minor influence on the volumetric flow rate, exhibiting a better consistency in the case of long extrusions. The percentage of surface cavities was proportional to the polymer fraction contained in the mix. From dimensional analyses, it was possible to conclude that PA12 reduced the degree of shrinkage during the drying phase, while it increased dimensional alterations occurring in the melting phase. The results showed that the dimensional error measured on the z-axis was always higher than that of the XY plane.Practical implicationsThe method proposed in this paper provides an alternative approach to reuse leftover powders from powder bed fusion processes via another additive manufacturing process. This offers an affordable and open-source solution to companies dealing with polymer powder bed fusion, allowing them to reduce their environmental impacts while expanding their production.Originality/valueThe paper presents an innovative additive manufacturing solution for powder reuse. Unlike the recycling methods in the body of literature, this solution does not require any intermediate transformation process, such as filament fabrication. Also, the cold material deposition enables the adoption of very inexpensive extrusion equipment. This preliminary study demonstrates the feasibility and the benefits of this process, paving the way for numerous future studies.

Effects of polyamide-11 powder refresh ratios in multi-jet fusion: A comparison of new and used powder

Abstract Multi-jet fusion (MJF) is a polymer powder bed process increasingly explored for the commercial fabrication of final products. The most popular materials used in MJF are polyamide 12 (PA12) and polyamide 11 (PA11), and the recommendation is to recycle at most 70% of the used powder. This results in significant amounts of used powder being discarded. In this paper we explored what happens if different ratios of new-to-used powder are used. Therefore, this research offers an insight in the thermal, morphological, and mechanical characteristics of all new, the recommended 30:70 mixed ratio, and all used PA11 powder. The thermal properties were evaluated through thermogravimetric analysis and differential scanning calorimetry. The morphology of the powders was examined through powder size distribution, powder flowability, and qualitatively through scanning electron microscopy and their printability and performance was assessed through tensile testing and porosity analysis using X-ray microcomputed tomography. We found that the samples fabricated with all used powder performed worse in tension than the other powder ratios, but its thermal properties did not significantly vary. We found that the used powder exhibited the greatest surface fractal which affected the porosity of the fabricated specimens. This difference was identified as the possible cause for the decrease in the tensile strength from 45 MPa to 39 MPa.

The Environmental Impacts of Metal Powder Bed Additive Manufacturing

AbstractAdditive manufacturing (AM) is widely recognized as a critical pillar of advanced manufacturing and is moving from the design shop to the factory floor. As AM processes become more popular, it is paramount that engineers and policymakers understand and then reduce their environmental impacts. This article structures the current work on the environmental impacts of metal powder bed processes: selective laser melting (SLM), direct metal laser sintering (DMLS), electron beam melting (EBM), and binder jetting (BJ). We review the potential benefits and pitfalls of AM in each phase of a part's lifecycle and in different application domains (e.g., remanufacturing and hybrid manufacturing). We highlight critical uncertainties and future research directions throughout. The environmental impacts of AM are sensitive to the specific production and use-phase context; however, several broad lessons can be extracted from the literature. Unlike in conventional manufacturing, powder bed production impacts are dominated by the generation of the direct energy (electricity) required to operate the AM machines. Combined with a more energy-intensive feedstock (metal powder), this means that powder bed production impacts are higher than in conventional manufacturing unless production volumes are very small (saving tool production impacts), and/or there are significant material savings through part light weighting or improved buy-to-fly ratios.

Radiative transfer, absorption, and reflection by metal powder beds in laser powder-bed processing

Laser powder-bed processing is widely employed in 3D printing. The technological processes strongly depend on such effective radiative-transfer properties of powder beds as the absorptance and the radiation penetration depth. However, it is still not completely clear what are the principal factors influencing these properties and what are the possible ranges of their variation. For theoretical investigation of the radiative transfer, a ray-tracing method is developed where the effective properties of powder beds are expanded in series of the reflectance of the solid-phase surface. Once the coefficients of the power series are calculated, they can be used for any combination wavelength/material thus facilitating parametric analysis. Powder beds are modeled by equal spheres packed in regular cubic-symmetry structures of various density. The calculated radiation penetration depth can vary from few particle diameters for close-packed structures with moderate solid-phase absorptance to few tens of particle diameters for less dense power beds of a highly reflecting material. The effective absorptance of the powder bed is revealed to decrease significantly with the packing density. The calculated dependence of the powder-bed absorptance versus the solid-phase absorptance and the density is validated by the known experimental data. The calculated angular distribution of the radiation reflected by a powder bed slightly deviates from the cosine-like distribution corresponding to the diffuse reflection law. It is validated by the known experimental data. A modified model of equivalent medium is proposed to approximate the obtained ray tracing results by analytic expressions.

Porosity, Hardness, Friction and Wear Performance Analysis of H13 SLM-Formed Samples

Selective laser melting (SLM), a type of additive manufacturing, is a powder bed process that makes use of a high-power laser beam to completely melt a thin layer of powder on a substrate, layer upon layer to form a solid part. This experimental study confirmed that laser power and scanning speed are indeed SLM’s most significant process parameters that affect porosity as stated in some literature and further studied the influence of laser power and/or laser-based volumetric energy density (VED) on hardness and friction and wear of SLM-formed samples. Full factorial design of experiment was carried out to study the influence of the two parameters on porosity with the help of Minitab 18 statistical software. The results obtained from this experiment were analyzed using analysis of variance. VED and laser power influence on hardness and friction and wear were studied on one factor at a time basis. Optimum laser power and scanning speed, optimum laser energy density values that achieve higher surface microhardness, minimum wear and porosity of H13 steel material were obtained from this experimental study.

An Innovative Approach on Directed Energy Deposition Optimization: A Study of the Process Environment’s Influence on the Quality of Ti-6Al-4V Samples

Blown powder additive manufacturing technologies are not restricted to the use of a process chamber. This feature allows to build larger components with respect to conventional powder bed processes. This peculiarity is mostly promising for manufacturing large components or repairing/rebuilding parts of large systems. The main downside of using an open environment, even if a protective shielding gas system is adopted, is the lack of control of process atmosphere. This is particularly critical for titanium alloys which are very sensitive to oxygen/nitrogen pick-up; they have a detrimental effect on ductility, by causing embrittlement and possibly leading to the formation of cracks. It is then important to address how environmental factors, such as process atmosphere and platform temperature, impact not only on the processability but also on the final component properties, both from a compositional and mechanical point of view. The correlations between these environmental factors and microstructure, interstitials content, grain size, and hardness were investigated. Moreover, the Hall–Petch equation was then adopted to additive manufacturing microstructures, characterized by a columnar grain morphology, and used to further investigate the relationship intercurring between grains and hardness and how different microstructures might influence this correlation.