Laser Powder Bed Fusion Technique Research Articles

Effect of Processing Parameters on Recrystallization During Hot Isostatic Pressing of Stellite-6 Fabricated Using Laser Powder Bed Fusion Technique

Crack-free Stellite-6 alloy was fabricated using the laser powder bed fusion technique equipped with a heating module as the first attempt. Single tracks were printed with a build plate heated to 400 °C to identify the processing window. Based on the melt pool dimensions, two combinations (sample A: 300 W/750 mm/s and sample B: 275 W/1000 mm/s) were identified to print the cubes. The as-printed microstructure comprised FCC-Co dendrites with M7C3 in the interdendritic region. W-rich M6C particles were found in the overlapping regions between the melt pools, matching the Scheil simulations. However, gas pores were observed due to the higher nitrogen and oxygen content of the feedstock requiring hot isostatic pressing (HIP) at 1250 °C and 150 MPa for 2 h. Sample A was partially recrystallized with slightly coarsened M7C3, while sample B underwent complete recrystallization followed by grain growth along with higher coarsening of the M7C3 after HIP. The varying recrystallization behavior can be attributed to the difference in residual stresses and grain aspect ratio in the as-built condition dictated by laser power and scanning speed. The microhardness after HIP was slightly higher than its wrought counterpart, indicating no severe impact of post-processing on the properties of Stellite-6 alloy.

A Novel Approach to Produce Metal–Metal Composites by Leveraging Immiscibility: Laser Powder Bed Fusion of Nanosilver‐Dispersed Titanium

The antimicrobial properties of silver ions are well known and effectively utilized in various biomedical applications. The efficacy of silver‐containing materials, particularly in terms of antimicrobial activity, heavily relies on the oxidizing surface, favoring nanosized silver features. However, producing such structures is challenging due to the high probability of miscibility in the liquid phase. Developing Ti–Ag composite alloys using the laser powder bed fusion technique with supported titanium powders and silver nanoparticles (AgNPs) represents a novel research pursuit, with no prior investigations reported. Incorporating AgNPs into titanium forms nanoislands, directly enhancing the antimicrobial efficacy of biomedical components. In this study, it is aimed to explore the solubility limit of silver in titanium and the feasibility of achieving finely dispersed silver islands. Experimental findings reveal that incorporating AgNPs into Ti‐based alloys results in discrete silver islands (0.01–0.02 μm2) within the microstructure, governed by the solubility limit of silver in titanium. In this study, valuable insights into producing components with augmented biocompatibility and proven antibacterial properties against Staphylococci infections are offered. The successful development of Ti–Ag composite alloys, featuring finely dispersed silver islands, opens promising avenues for biomedical applications, enhancing their antibacterial characteristics and improving patient outcomes.

Investigating the Effects of Boron Nitride on Mechanical Properties of CoCrFeNiMn Composites

High‐entropy alloys (HEAs) are gaining attention for their exceptional properties but achieving precision and surface quality in powder metallurgy (PM) can be challenging. This study investigates the mechanical properties of CoCrFeNiMn HEAs produced through the flake powder metallurgy (FPM) technique and laser powder bed fusion (LPBF) preservative industrial, which established outstanding antiwear properties. To assess the enhancement of mechanical behavior and wear resistance by incorporating boron nitride (BN) into CoCrFeNiMn composites is fabricated via FPM. By incorporating BN into the composites, the mechanical behavior is significantly enhanced, leading to improved resistance against wear. Furthermore, the study delivers comprehensions into the serration behavior microstructure and shear localization in a high‐strain‐rate‐deformed CoCrFeMnNi entropy‐high alloy produces through metallurgy in powder. The serration behavior of the CoCrFeMnNi HEA is discussed concerning strain rate and temperature. Accordingly, the study employs the LPBF technique to fabricate the CoCrFeMnNi alloy from the prepared flakes. Microstructural characterization using scanning electron microscopy and X‐ray diffraction techniques to explore phase distribution, grain size, and possible segregation in the CoCrFeMnNi alloy produced through FPM‐LPBF is performed. In this particular investigation, a gradient microstructure is achieved through fusion in a laser‐powder bed of CoCrFeMnNi HEA onto highly deformed equal‐atomic HEA sheets. The resulting combination of partially recrystallized regions, exhibiting elevated yield strength, and fully recrystallized regions, demonstrates enhanced strain hardenability and elongation, and yields superior mechanical properties. The results obtained from the FPM‐LPBF CoCrFeMnNi alloy will be compared with those of conventionally processed CoCrFeMnNi to highlight the advantages and improvements achieved through the proposed method. The study findings reveal that the fundamental understanding of HEAs’ behavior under LPBF with FPM affords valuable insights into optimizing the processing parameters and achieving superior mechanical attributes.

Tribo-technological features of laser powder bed fusion process: scratch and wear resistance of AlSi10Mg aluminium alloy

Mechanical systems, regardless of their complexity, very often require that different parts must move relative to each other by sliding their surfaces, therefore appropriate tribological properties are needed. This request appears particularly evident for components fabricated through Metal Additive Manufacturing processes, due to their typical high surface roughness. In the current study, the Laser Powder Bed Fusion technique with optimized parameters is used to produce samples made of AlSi10Mg alloy. Their tribo-technological properties are investigated through progressive load scratch and dry ball-on-plate wear tests. Along with a global characterization, a local analysis has been performed to identify any variations induced by the building direction. The friction coefficient and the wear rate are generally higher than as-cast specimens. Finally, local trends suggest that the central parts of the samples average offer higher resistance to wear and scratch than the outer areas.

Mechanical property, corrosion behavior and cytocompatibility of CoCrMo for dental application: A comparative study of cast and laser powder bed fusion

In this work, by employing powders sourced directly from the original ingot for additive manufacturing, we enabled a comparative overview of the performance between CoCrMo manufactured via laser powder bed fusion (LPBF) and those in their original cast condition. Microstructural analysis revealed that the cast (CT) alloy predominantly consisted of coarse grains with distribution of sigma phase, while the LPBF process resulted in a refined grain structure devoid of the sigma phase. The tensile strength tests demonstrated that the LPBF-derived CoCrMo alloy had substantially greater tensile strength, and ductility compared to CT alloy. Corrosion tests indicated superior corrosion resistance in the LPBF alloy, albeit with a lower metal ion release. In vitro assays confirmed that LPBF CoCrMo alloys displayed favorable cytocompatibility. Consequently, it is concluded that the CoCrMo alloy processed through laser powder bed fusion exhibited enhanced mechanical performance and corrosion resistance. These improvements are primarily attributed to the transformation of the original coarse columnar grain structure through the LPBF technique.

Oxides improve the strength of Zn-0.5Mn-0.5Mg alloys proceeded by laser powder bed fusion

Laser powder bed fusion has recently been adopted to fabricate biodegradable Zn alloys. But the mechanical properties need to be further improved to meet the requirements for natural bone implants. In this study, a ternary Zn-0.5Mn-0.5Mg biodegradable alloy is prepared by laser powder bed fusion technique. The as-printed sample shows a large compressive yield strength of 267 MPa and considerable ductility that the sample maintains its integrity after 50 % compression. The improved strength is mainly attributed to the formation of brittle Zn oxides, Mn oxides and Mg oxides which induce lattice distortion. These oxides fragment easily during the compression and reduce the stress concentration, resulting in significant ductility. More importantly, the as-printed sample shows a moderate degradation rate of 0.08 mm/year after immersing in the simulated body fluid solution for 7 days. In addition, the sample has MC3T3-E1 cell viabilities higher than 75 %, showing no-toxicity characteristic. This study demonstrates that laser powder bed fusion Zn-Mn-Mg alloy is a promising candidate for biodegradable materials and proposes a novel route to tailor the mechanical properties of additive-manufactured Zn alloys by oxides compositing.

Role of the γ′′ precipitation at the cell boundaries in enhancing the creep resistance of additively manufactured Inconel 718 alloy using the laser powder bed fusion technique

Laser powder bed fusion (LPBF) manufactured Inconel 718 superalloy (IN718) parts exhibit inferior creep properties compared to their conventionally manufactured (CM) counterparts due to the unique microstructural features associated with them. In this study, two different heat treatment schedules were employed, to critically examine role of distinct microstructural features associated with LPBF on the creep performance of LPBF IN718. Experimental results reveal that the creep performance is controlled by the Laves and γ′′ phases, as well as the cellular structure. Specially, the effective dissolution of Laves phases that are distributed along the grain and cellular boundaries in the as-fabricated state during solution treatment reduces the cavity nucleation sites and hence, extends the creep lifetime. The release of Nb into the matrix contributes to the precipitation of primary strengthening γ′′ phase during subsequent aging, enhancing the creep resistance. More importantly, the formation of a unique cellular structure with densely distributed γ′′ phase along the cellular boundaries, which exhibits high impediment of dislocation movement and inhibition of crack propagation, results in superior creep performance. The findings of the current study provide an effective heat treatment strategy for achieving high creep performance in LPBF nickel-based superalloys.

Stochastic or deterministic: Duality of fatigue behaviour of 3D-printed meta-biomaterials

The two deformation modes of meta-biomaterials during cyclic loading have been revealed: stochastic and deterministic strut failure processes. Biomimetic Voronoi structures with a range of strut thicknesses and number of cells per unit volume are printed. We show that when the strut thickness is 200 μm or above, the fatigue fracture process of the lattice is deterministic and the fatigue scatters are below 15%. As the strut is thinned to 150 μm, the local failures occur randomly within the structure, which may lead to a high fatigue scatter (>30%). The two distinct behaviours result from the processing limit of the laser powder bed fusion technique. We demonstrate that the fatigue scatter and the location of the failure process within the lattice are related to the probability that a cluster of unconnected struts larger than a critical value can exist within the lattice. Unlike solid parts, porosity hardly triggers any damage in metallic lattices during cyclic deformation. The discovery of the Janus-like failure process opens up our understanding of meta-biomaterials and defines the pathway towards the design of mechanically durable intricate implants.

Feasibility of using ground Al-Al2O3 composite powders in laser powder bed fusion

The reincorporation of residues in the productive cycle helps reduce CO2 emissions and non-renewable resources extraction. Therefore, the present work studies the feasibility of reincorporating an aluminum residue in the productive cycle by means of an additive manufacturing technique. In this context, other issues considered are the importance of aluminum alloys, the improvement of their properties by adding alumina making composites materials, and issues that must be overcome when printing parts by laser powder bed fusion using a mix of Al and alumina powders. This work evaluates the suitability of Al alloy - alumina composite powders obtained by grinding Al alloy chips from sawing. Laser power and scanning speed were varied until the designed samples were obtained. The findings show that is possible to use powder obtained by grinding Al chips in the laser powder bed fusion technique to obtain Al-Al2O3 composites which exhibits hardness of 226 HV ± 34.3.

Synergistic improvement of pitting and wear resistance of laser powder bed fusion 420 stainless steel reinforced by size-controlled spherical cast tungsten carbides

The spherical cast WC/W2C is selected to produce a martensitic stainless steel-based composite using the laser powder bed fusion technique. W and C reacted with Fe and Cr, creating a strong bond between the particles and the matrix, reducing the wear rate by over 98 %. W and C diffuse to the matrix, increasing the hardness over 100 HV0.5. The interface between cast WC/W2C and matrix is sensitive to pitting corrosion through galvanic effects. However, the formation of austenite and WO3 from spherical cast WC/W2C decomposition improves the critical pitting potential and passive film stability.

Exploring VHCF response in L-PBF AlSi7Mg Alloy: Influence of T6 heat treatment on microstructural characteristics and defect distribution

Laser Powder Bed Fusion (L-PBF) is a popular technique for making intricate parts in various fields. Assessing the load-bearing capacity of components fabricated through L-PBF technique is crucial for broadening their applications across various industrial sectors. While prior research has primarily concentrated on static loads, cyclic loading is critical in real-world engineering applications. The purpose of this study is to investigate the influence of T6 heat treatment on the very high cycle fatigue (VHCF) performance of AlSi7Mg alloy fabricated using L-PBF technique by considering microstructural alteration and defect statistics. This study shows that the investigated heat treatment reduced VHCF response of the alloy. This is attributed to increased hydrogen and oxide porosity in conjunction with their increased diametral sizes along with microstructural alteration. The obtained results bring us closer to better understand and improve the use of the AlSi7Mg alloy in additive manufacturing. This offers a viable option for industries looking to benefit from the advantages of the L-PBF technique for manufacturing components.

Effect of heat treatment on the microstructure and properties of CuCrZr prepared by laser powder bed fusion

In this paper, CuCrZr alloys were prepared by laser powder bed fusion technique. Under optimum forming process conditions, a relative density of 99.7% was obtained and the specimens were analyzed for microstructure and properties. To enhance the mechanical properties of the copper alloy, the specimens are post-treated using both solution aging and direct aging heat treatments. The variation and influence mechanism of microstructure and mechanical properties, thermal conductivity and electrical conductivity were studied and analyzed. With direct aging heat treatment a large number of Cr nanoprecipitates can be obtained, significantly improving the properties of the alloy. The best synthesis properties obtained at an aging temperature of 450 °C were: microhardness 168.7 ± 3.1 HV, ultimate tensile strength 481.7 ± 7.6 MPa, electrical conductivity 73.9 ± 0.9 %IACS, thermal conductivity 314.3 ± 5.3 W/(m·K).

Post-Processing Effect on the Corrosion Resistance of Super Duplex Stainless Steel Produced by Laser Powder Bed Fusion.

This study examines the microstructural characteristics and corrosion resistance of super duplex stainless steel (SDSS) produced through laser powder bed fusion (LPBF). The analysis shows that the as-printed samples mainly exhibit a ferritic microstructure, which is due to the fast-cooling rates of the LPBF technique. X-ray and microstructure analyses reveal the presence of minor austenite phases in the ferritic matrix. The process of solution annealing led to a more balanced microstructure. Analyses of corrosion resistance, such as potentiodynamic polarization tests and EIS, indicate that heat treatment has a significant impact on the corrosion behavior of SDSS. Solution annealing and stress relieving at 400 °C for 1 h can improve corrosion resistance by increasing polarization resistance and favorable EIS parameters. However, stress relieving at 550 °C for 5 h may reduce the material's corrosion resistance due to the formation of chromium nitride. Therefore, stress relieving at 400 °C for 1 h is a practical method to significantly enhance the corrosion resistance of LPBF-printed SDSS. This method offers a balance between microstructural integrity and material performance.

Effect of design parameters on auxetic behavior and stiffness of additively manufactured 316L stainless steel

Auxetic structures, characterized by showing negative Poisson's ratio (ʋ) when loaded, are cellular metamaterials consisting of connected struts in repeating unit cells. The mechanical behavior of auxetics depends on dimensions of the unit cell such as height and length of the unit cell, strut thickness (St), and orientation angle (θ) of the struts. The present study investigates effects of variations in St and θ on ʋ and stiffness (E) of additively manufactured 316L stainless steel with re-entrant honeycomb auxetics fabricated by laser powder bed fusion technique. Poisson's ratio was acquired through linear elastic simulations via finite element analysis (FEA) and verified experimentally through digital image correlation (DIC) facility attached to tensile tests. The design of the auxetic patterns entailed a simulation of thirty-five distinct models, incorporating St values of 0.4–1.6 mm, as well as θ values of 70–90°. In comparison, experimental validation was conducted on nine specimens, featuring St values of 0.6–1.4 mm, and θ values of 70–80°. FEA and experimental results obtained by DIC exhibited ʋ values of −5.23 to −0.3 (for St 0.6-1.4 mm and θ 70–80°), displaying increased ʋ with reductions in both St and/or θ. Meanwhile, E increased with St increase or θ decrease, exhibiting values of 18.9–72 GPa, which could be optimized to fit with human bones stiffness as potential orthopedics implantation in future.

Nanometer-scale porosity evolution and mechanical properties of additively manufactured 17-4PH stainless steel

Understanding of the microstructure and mechanical properties of additively manufactured (AM) 17-4PH stainless steel has matured significantly, but combined wrought-level strength and ductility has yet to be achieved. Identifying the microstructural obstacle(s) impeding this milestone is critical for many future applications and industries interested in this AM alloy. In this work, microstructure, mechanical properties, and fracture behavior is evaluated for AM 17-4PH built via the laser powder bed fusion technique (LPBF) and heat treated via a broad range of techniques to achieve wrought-level 17-4PH strength. The highest strength/ductility was achieved with a two-stage hot isostatic press (HIP) and solution anneal (SA) treatment followed by an aging heat treatment, but wrought-level ductility could not be matched. Persistent nano-porosity (0.06–0.23 μm) was identified and correlated to fracture surface dimpling (R2 = 0.73–0.85) indicating a possible role in this ductility limitation. Contextualization of this study's mechanical properties dataset within the literature suggests that this observation is endemic to the current state-of-the-art processing techniques for AM 17-4PH.

Blistering and retention behavior of laser powder bed fused tungsten alloys under hydrogen plasma irradiation

In this study, pure tungsten (W) fabricated by powder metallurgy and laser powder bed fusion (LPBF) formed W-Ta and W-ZrC alloys were exposed to hydrogen plasma. Severe blistering was found in LPBFed W-Ta specimens due to a strong [111] crystallographic texture and the large number of particle-matrix interfaces in the LPBFed W-ZrC inhibits the blister growth. The retention of LPBFed W alloys is lower than that of pure W due to the presence of large columnar grains and cracks. The results highlight the capability of tailoring the microstructures of W alloys by the LPBF technique to achieve improved plasma-compatible performance.

Modelling and characterization of novel honeycomb structures with mass gradient produced by additive manufacturing

The dissemination of additive manufacturing methods has facilitated the design and production of complex structures which have a high strength-to-weight ratio. Cellular materials such as honeycombs have low-weight and high capacity to absorb energy which makes them desirable for the aerospace and automotive industries. The present work covers the study and comparison of metal-based regular honeycombs and functionally graded honeycombs. The latter encompass radial and linear/longitudinal gradients. Three repeating unit cells were studied: regular hexagons, Plateau and lotus. The structures were produced in aluminium using the laser powder bed fusion technique. Selected samples were submitted to a stress-relieving heat treatment. Numerical and experimental methods were used to assess the in-plane compressive properties. Finite element analysis was used to obtain the simulated force–displacement curves of each structure, allowing for the calculation of specific stiffness, absorbed energy and yield strength. The experimental method consisted of the compression of three specimens of three types of regular structures with and without stress-relieving heat treatment. The heat treatment reduced the yield strength and stiffness whilst increasing the ductility of the samples. The mechanical behaviour of the structures was found to depend upon a combined effect of the type of gradient, relative density, and unit cell structure. The results showed that an increase in the relative density would enhance the specific mechanical properties. The lotus configuration displayed the highest specific mechanical properties, as its geometry reduces the stress concentrations. The numerical results showed a reasonable match with the experimental results.

Improving the mechanical properties of laser powder bed fused AlSi10Mg alloys by eliminating the inevitable micro-voids via hot forging

PurposeThe metallic alloys and their components fabricated via laser powder bed fusion (LPBF) suffer from the microvoids formed inevitably due to the extreme solidification rate during fabrication, which are impossible to be removed by heat treatment. This paper aims to remove those microvoids in as-built AlSi10Mg alloys by hot forging and enhance their mechanical properties.Design/methodology/approachAlSi10Mg samples were built using prealloyed powder with a set of optimized LPBF parameters, viz. 350 W of laser power, 1,170 mm/s of scan speed, 50 µm of layer thickness and 0.24 mm of hatch spacing. As-built samples were preheated to 430°C followed by immediate pressing with two different thickness reductions of 10% and 35%. The effect of hot forging on the microstructure was analyzed by means of X-ray diffraction, scanning electron microscopy, electron backscattered diffraction and transmission electron microscopy. Tensile tests were performed to reveal the effect of hot forging on the mechanical properties.FindingsBy using hot forging, the large number of microvoids in both as-built and post heat-treated samples were mostly healed. Moreover, the Si particles were finer in forged condition (∼150 nm) compared with those in heat-treated condition (∼300 nm). Tensile tests showed that compared with heat treatment, the hot forging process could noticeably increase tensile strength at no expense of ductility. Consequently, the toughness (integration of tensile stress and strain) of forged alloy increased by ∼86% and ∼24% compared with as-built and heat-treated alloys, respectively.Originality/valueHot forging can effectively remove the inevitable microvoids in metals fabricated via LPBF, which is beneficial to the mechanical properties. These findings are inspiring for the evolution of the LPBF technique to eliminate the microvoids and boost the mechanical properties of metals fabricated via LPBF.

Strengthening aluminum matrix composite with additively manufactured 316L stainless steel lattice reinforcement: Processing methodology, mechanical performance and deformation mechanism

This study investigates various processing approaches, interface characteristics, and mechanical properties of an aluminum (Al) matrix composite reinforced with additively manufactured (AM) 316L stainless-steel (SS) lattice. The AM-316L-SS lattice, boasting a 30 % infill density, was fabricated using the laser powder bed fusion technique. The Al-matrix was integrated with the AM-316L-SS reinforcement through experimentation involving pre-stirring of the molten Al under pressurized and unpressurized die-casting conditions. A well-bonded interface, with cohesive regions, was obtained in the pre-stirred structures. In contrast, regions of decohesion were displayed in cast structures without pre-stirring, leading to the presence of pores and the manifestation of imperfect bond interfaces. Compression tests conducted on the sound composite demonstrated enhanced mechanical properties, with a compressive strength of approximately 163 MPa, significantly higher than that of the pure Al-matrix (approximately 80 MPa). Localized interface cracking was initiated by stress gradients and plastic deformation, leading to microcrack propagation into the Al-matrix.

Tradeoff of structural layouts of a compact heat exchanger additively manufactured for space exploration

The innovative thermal management system named Two-Phase Mechanically Pumped Loop (2PMPL) has been investigated to design probes for Venus exploration. This study aims integrating the 2PMPL evaporator inside the probe shell, using the Laser Powder Bed Fusion technique, to reduce the thermal system size and to increase the payload. In this paper, four evaporator designs have been developed and compared to the latest available reference solution. The overall assessment of those designs has been performed by comparing the results of basic Computational Fluid Dynamics analysis, structural behavior, mass and Three-Phase Contact Line (TPCL) length, highlighting specific strengths of each solution.