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![Figure 3. Schematic drawing of a generic pattern of single scan lines [78].](publication/334100767/figure/fig3/AS:774933894406144@1561770046131/Schematic-drawing-of-a-generic-pattern-of-single-scan-lines-78_Q320.jpg)
In this paper, the capability of laser powder bed fusion (L-PBF) systems to process stainless steel alloys is reviewed. Several classes of stainless steels are analyzed (i.e., austenitic, martensitic, precipitation hardening and duplex), showing the possibility of satisfactorily processing this class of materials and suggesting an enlargement of th...
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... is of major relevance to remember that, unlike conventional processes, all AM technologies are producing the alloy and the specific geometry to be put in service simultaneously. This means that process parameters usually related to the material quality (e.g., laser parameters determining melting and solidification behavior) now directly affect the performance [76] of the final components, as shown in Figure 2. The result is that, even if some post processing is projected (e.g., heat treatments, machining), material-related defects arising during 3D printing will cause the artefacts to be discarded at the end of the whole cycle, which can take up to weeks of work for large components. ...
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Pressure equipment poses a high risk of harming people and the environment in case of failure. They are, therefore, highly regulated by the Pressure Equipment Directive. To enable laser powder bed fusion of metals (PBF-LB/M) for the manufacturing of such components, component appearance and quality need to be characterized and qualified for each sp...
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... Laser powder bed fusion of metals (PBF-LB/M) is an AM route that utilizes a guided laser beam to selectively melt metal powders layer-by-layer in an inert atmosphere and facilitates the production of intricately designed metal components. PBF-LB/M has gained significant industrial interest since its advent in the 1990s due to its unparalleled precision, minimal surface waviness, ability to achieve near 100% relative densities, versatility in producing intricate and complex structures, and efficacy in reducing oxide impurities while production due to presence of inert atmosphere which is crucial to preserve corrosion and fatigue resistance in metal alloys since oxides can act as crack initiators [69]. In the fourth stage, the manufacturing process starts with placing metal powders within the powder-bed space, the quantity being dependent on the height of the part. ...
Laser-based powder bed fusion of metals (PBF-LB/M) is an additive manufacturing technology gaining attention in various industries due to its ability to allow design flexibility to fabricate complex structures precisely. In the marine sector, there is a growing interest in PBF-LB/M because of its potential to produce components such as heat exchangers, propeller shafts, impellers, and exhaust manifolds with lesser lead time, reduced cost, and customization. While 316L stainless steel has been a popular choice for marine applications due to its excellent corrosion resistance in seawater atmosphere, nickel-free duplex stainless steel (NiFDSS) emerges as a cost-effective and lightweight alternative, prompting research into its suitability for PBF-LB/M fabrication.
This thesis investigates the optimization of process parameters in PBF-LB/M of NiFDSS to attain defect-free samples. Experimental analyses focus on understanding the microstructural transformations of NiFDSS, transitioning from a fully ferritic to a duplex microstructure post-heat treatment. The study evaluates the tribological and corrosion properties of NiFDSS using a tribocorrosion setup under an artificial seawater environment.
Results obtained in this study indicate a relative density achievement of 98.83% for PBF-LB/Med NiFDSS. Corrosion testing reveals superior corrosion resistance of NiFDSS, both in its as-built and heat-treated condition, compared to 316L. However, 316L exhibits better wear resistance characteristics. Further process optimization is needed to enhance the wear behavior of NiFDSS samples.
Overall, the study underscores the potential of NiFDSS as a viable alternative for marine components, particularly in applications where the wear rates are not very high, leveraging the design flexibility of PBF-LB/M to meet industry demands effectively.
... This layer-by-layer process continues until a three-dimensional (3D) part is obtained. L-PBF processes, distinguished by using a powder feedstock spread over a powder bed layer and selectively melted by a laser according to a CAD file, are employed to build components in an inert atmosphere, such as Argon [10][11][12][13][14][15]. Alloys like steel, titanium, aluminum, and nickel-based superalloys are frequently used to produce L-PBF components [13,16]. ...
This research aims to enhance the understanding of the interrelationships among the manufacturing process, microstructure, and mechanical properties in the Laser Powder Bed Fusion (L-PBF) of SAE 316L stainless steel (SS), which can lead to the appearance of undesirable phases, like sigma (σ). As part of this investigation, as-built samples underwent solubilization heat treatment (HT), primarily targeting the dissolution of the σ phase and microstructure homogenization, with a subsequent assessment of its impact on hardness. The study reveals the efficacy of HT in reducing σ phase content, particularly following treatments at 950°C and 1,050°C for 2 h. Notably, the dissolution of the process-induced microstructure becomes progressively significant within the temperature range of 800-950°C for 2 h. Furthermore, the study identifies a hardening effect associated with the process-induced microstructure on the samples. Remarkably, the sample exhibiting the highest hardness value featured a substantial σ phase content and maintained the process-induced structure after HT.
... The microstructure of 17-4 PH SS is characterized by the precipitation of copper-rich phases in a martensitic matrix [7]. Concerning AM 17-4 PH SS parts, they have shown good mechanical and corrosion properties in their as-built conditions [8,9], fabricated by Selective Laser Melting (SLM) [10,11], laser deposition, and supersonic laser deposition [12]. ...
Additive manufacturing (AM) or 3D printing of metals is gaining popularity due to its flexibility in fabricating parts with highly complex designs, as well as simplifying manufacturing steps and optimizing process times. In this investigation, 17-4 PH stainless steel was additively manufactured using Laser-Powder Bed Fusion (L-PBF), followed by functionalization through a DUPLEX treatment. This treatment involved a plasma-assisted nitriding process, followed by deposition of an arc-PVD c-Al0.7Cr0.3N hard coating. The microstructural modifications resulting from plasma nitriding (such as the formation of Fe2,3N and Fe4N, and the αN or expanded martensite phases), and the surface improvements with the c-Al0.7Cr0.3N coating on the 3D-printed 17-4 PH steel, are evaluated in comparison to conventionally manufactured 17-4 PH steel. These microstructural characteristics are correlated with the mechanical response of the treated surfaces. As a result of the plasma nitriding process, the hardness of the 3D-printed 17-4 PH SS increased by approximately 260%. The wear, measured through dynamic and static scratch-testing, was reduced by approximately 31%. This improvement was attributed to the modification of adhesive failure mechanisms, leading to a reduction in wear volume, improved coating adhesion, and enhanced scratch resistance.
... It is well known that heat treatment leads to the precipitation of Curich nanoprecipitates which play an important role in the increase of the hardness in the thermal treated 17-4 PH SS by hindering the dislocation movements and producing a semi-coherent interface [36,37]. Moreover, the amount of austenite phase observed in SLM and FFF samples was higher than in the wrought sample and, as it is known, the austenite phase has influence in the mechanical properties reducing the hardness [38]. ...
... The possibility of complex internal geometries allows for greater freedom of design than previously possible [1]. The most commonly used method for AM, powder bed fusion (PBF), spreads successive layers of fine metal powder to be selectively melted by a highpower processing laser to form the desired geometry [2][3][4]. This laser melting process is dominated by similar keyhole and vapor depression dynamics found in laser welding [5]. ...
Laser additive manufacturing (AM) promises direct metal 3D printing, but is held back by defects and process instabilities, giving rise to a need for in situ process monitoring. Inline coherent imaging (ICI) has proven effective for in situ, direct measurements of vapor depression depth and shape in AM and laser welding but struggles to track turbulent interfaces due to poor coupling back into a single-mode fiber and the presence of artifacts. By z-domain multiplexing, we achieve phase-sensitive image consolidation, automatically attenuating autocorrelation artifacts and improving interface tracking rates by 58% in signal-starved applications.
... Laser Powder Bed Fusion (L-PBF), also known as Selective Laser Melting (SLM), is the technique that delivers optimal results in achieving precise surface smoothness and tolerances for the manufacture of metallic components. L-PBF is based on fusing thin layers of metal powder, known as "layers", using thermal energy generated by a laser source [9]. During this procedure, the laser beam fully melts the metal powder particles due to the high energy input. ...
Additive manufacturing allows the creation of geometries otherwise impossible to achieve through traditional technologies in mechanical components. These geometries can be obtained using algorithms to optimize the mass distribution. Topology Optimization algorithms are one of the tools most applied in design for additive manufacturing and lightweight engineering. These optimization techniques require Finite Element Method tools to evaluate and compare the mechanical behavior of different geometrical solutions. The optimization results are closely related to boundary conditions, objectives, and constraints. Therefore, one of the issues is the necessity to evaluate different parameter settings to improve the result in terms of light weight, strength, and easy printability. This article shows a working method for using topological optimization to lighten a connecting rod. The resultant model is optimized considering Additive Manufacturing.
... As the CAD data dictates, the SLM uses a laser beam to selectively melt and fuse metal powder layer by layer. This unique feature of building parts directly from a 3D CAD model promotes flexibility in design, functional integration, part customization, elimination of fixturing and tooling costs, short lead-time, material saving, weight reduction, and elimination of multiple process steps, compared to conventional processing techniques [4][5][6]. These advantages make it a leading candidate for manufacturing mission-critical components for aerospace, medical, energy, and automotive applications [1,7]. ...
Selective laser melting (SLM) process produces high-performance metal parts using a layer-by-layer technique involving various influential factors. Nevertheless, there is a research gap in predictive models for the performance of SLM-processed 316L stainless steel, specifically concerning the effect of process parameters and their interactions. To address this, a systematic approach based on Taguchi design and analysis of variance (ANOVA) was used to optimize the SLM processing of 316L stainless steel. An experimental plan was set up using an L9 orthogonal array, with laser power, hatch spacing, and scan speed as input variables, each with three levels. Optical microscopy was used to analyze microstructure and porosity, while response variables, including relative density, surface roughness, hardness, and tensile properties, were measured. Regression models and response surface method (RSM) contour plots modeling the relationship between the input factors and the response variables were also presented. The main aim of this study is to provide valuable design tools for predicting and optimizing the performance of 316L SS processed by SLM. Results showed high densification levels (up to 99.97%) and excellent mechanical properties, surpassing conventionally processed 316L SS. The sample produced at P = 170W, h = 0.08 mm, and v = 1000 mm/s exhibited the highest tensile properties with a yield strength of 421 MPa, hardness of 245 HV, and elongation at failure of 42%. For the variation range, ANOVA results showed that hatch spacing was the most significant parameter influencing relative density and mechanical properties. The scan speed and hatch spacing increase negatively impacted all properties due to low densification. Moreover, increased laser power can melt the powder, resulting in less porosity. As a result, surface finish and ductility are improved. Overall, the findings of this paper contribute to the fabrication of stainless steel 316L using SLM with optimized parameters.
... Given the challenges linked to machining and shaping duplex stainless steels, and recognizing the limitations of powder metallurgy free-form fabrication, such as the tendency to yield porous structures, utilizing laser powder bed fusion (LPBF) as an additive manufacturing (AM) technology for duplex stainless steels has become a potential state of the art in manufacturing [9]. Wire arc additive manufacturing (WAAM) [10,11], laserdirected energy deposition (L-DED) [12], and laser powder bed fusion (LPBF) represent the dominant metal AM methods for the production of DSS and SDSS parts [13]. ...
The aim of this paper was to compare duplex (DSS) and super duplex stainless steel processed by laser powder bed fusion (LPBF) based on the process parameters and microstructure–nanomechanical property relationships. Each alloy was investigated with respect to its feedstock powder characteristics. Optimum process parameters including scanning speed, laser power, beam diameter, laser energy density, and layer thickness were defined for each alloy, and near-fully dense parts (>99.9%) were produced. Microstructural analysis was performed via optical (OM), scanning electron microscopy (SEM) and electron backscatter diffraction (EBSD). The samples were subjected to stress relief and high-temperature annealing. EBSD revealed the crystallographic orientation and quantified the phases in the as-built and annealed sample conditions. The as-built samples revealed a fully ferritic microstructure with a small amount of grain boundary austenite in the SDSS microstructure. High-temperature solution annealing resulted in the desired duplex microstructure for both alloys. There were no secondary phases present in the microstructure after both heat treatments. Nanoindentation generated nanomechanical (modulus) mapping grids and quantified the nanomechanical (both hardness and modulus) response; plasticity and stress relief were also assessed in all three conditions (as-built, stress-relieved, and annealed) in both DSS and SDSS. Austenite formation in the annealed condition contributed to lower hardness levels (~4.3–4.8 Gpa) and higher plastic deformation compared to the as-built (~5.7–6.3 Gpa) and stress-relieved conditions (~4.8–5.8 Gpa) for both alloys. SDSS featured a ~60% austenite volume fraction in its annealed and quenched microstructure, attributed to its higher nickel and nitrogen contents compared to DSS, which exhibited a ~30% austenite volume fraction.
... The typical precipitation heat treatment of maraging and PH-SS, solution annealing and aging (SA), involves solution annealing in the austenite field (between 800 and 1040 • C according to the steel conformal cooling channels with increased cooling efficiency, leading to higher productivity and part surface quality [12][13][14][15]. PH-SS are easily manufacturable by LPBF due to their low C content, leading to a reduced risk of crack formation [14,[16][17][18]. The as-built (AB) microstructure of LPBF-manufactured PH-SS consists of melt pool/scan track boundaries, a martensite microstructure with oriented grains, and a cellular solidification sub-structure, and exhibits relatively low hardness and strength due to the lack of strengthening precipitates comparable to condition A for conventionally manufactured PH-SS [8,14,17,[19][20][21][22][23][24][25][26][27][28][29][30]. ...
... The AB microstructure of Cu-bearing 17-4 PH and 15-5 PH steels can possess significant amounts of metastable, retained γ-austenite, depending on the powder atomisation and LPBF inert gas atmosphere [18,[31][32][33][34][35][36][37][38][39][40]. On the other hand, the AB structure of PH-SS, with a composition similar to PH 13-8 Mo (for example, stainless steels CX, Corrax, and M789, such as the one investigated in the present work), is inherently martensitic, with only low amounts of retained austenite [14,[16][17][18][19][20]22,23,25,41,42]. Moreover, LPBF-manufactured PH-SS can be strengthened by a direct aging treatment (DA), with no solution annealing, due to the martensite microstructure with high alloying supersaturation in the AB condition resulting from the extremely high cooling rates of the LPBF process [19,22,29,43]. ...
The combination of precipitation-hardening stainless steels (PH-SS) and laser powder bed fusion (LPBF) enables the manufacturing of tools for plastic injection moulding with optimised geometry and conformal cooling channels, with potential benefits in terms of productivity, part quality, and tool duration. Moreover, the suitability of LPBF-manufactured PH-SS in the as-built (AB) condition to be age-hardened through a direct aging (DA) treatment enables a great heat treatment simplification with respect to the traditional solution annealing and aging treatment (SA). However, plastic injection moulding tools experience severe thermal cycles during their service, which can lead to over-aging of PH-SS and thus shorten tool life. Therefore, proper thermal stability is required to ensure adequate tool life and reliability. The aim of the present work is to investigate the aging and over-aging behaviour of a commercially available PH-SS (AMPO M789) manufactured by LPBF in the AB condition and after a solution-annealing treatment in order to evaluate the effect of the heat treatment condition on the microstructure and the aging and over-aging response, aiming at assessing its feasibility for plastic injection moulding applications. The AB microstructure features melt pool borders, oriented martensite grains, and a cellular solidification sub-structure, and was retained during aging and over-aging. On the other hand, a homogeneous and isotropic martensite structure was present after solution annealing and quenching, with no melt pool borders, cellular structure, or oriented grains. The results indicate no significant difference between AB and solution-annealed and quenched specimens in terms of aging and over-aging behaviour and peak hardness (in the range 580–600 HV), despite the considerably different microstructures. Over-aging was attributed to both the coarsening of strengthening precipitates and martensite-to-austenite reversion (up to ~11 vol.%) upon prolonged exposure to high temperature. Based on the results, guidelines to aid the selection of the most suitable heat treatment procedure are proposed.
... They also allow the diffusion of segregated alloying elements. While through the ageing treatments, the formation of precipitates takes place, which helps to increase the mechanical properties of the material [123][124][125]. Furthermore, oxidation phenomena occur during thermal treatments which form a protective oxide layer on a wide range of materials. ...
... Furthermore, oxidation phenomena occur during thermal treatments which form a protective oxide layer on a wide range of materials. This helps to increase the performance in terms of corrosion and wear resistance [124][125][126]. ...
