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•Recent developments in multi-material additive manufacturing (MMAM) were comprehensively reviewed.•The applications of MMAM were discussed regarding various materials and AM ...methods.•The aspect of MMAM design, modeling, post-processing, and analysis was summarized.•Limitations, challenges, future trends of MMAM were highlighted.
Extensive research on nature-inspired cellular metamaterials has globally inspired innovations using single material and limited multifunctionality. Additive manufacturing (AM) of intricate geometries using multi-materials provides additional functionality, environmental adaptation, and improved mechanical properties. Recently, several studies have been conducted on multi-material additive manufacturing (MMAM) technologies, including multi-materials, methodologies, design, and optimization. However, in the past six years, very few or no systematic and complete reviews have been conducted in this research domain. This review intends to comprehensively summarize MMAM systems and the working principles of its fundamental processes. Herein, the Multi-material combinations and their design, modeling, and analysis strategies have been reviewed systematically. In particular, the focus is on applications and opportunities for using MMAM for several industries and postprocessing MMAM fabricated parts. Furthermore, this review identified the limitations and challenges of existing software packages, MMAM processes, materials, and joining mechanisms, especially at the multi-material interfaces. Finally, we discuss the possible strategies to overcome the aforementioned technological challenges and state the future directions, which will provide insights to researchers and engineers designing and manufacturing complex nature-inspired objects.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZAGLJ, ZRSKP
Structural evaluation of ionic additions in calcium phosphates that enhance their performance is a long-lasting area of research in the field of biomedical materials. Ionic incorporation in ...β-tricalcium phosphate (β-TCP) structures is indispensable for obtaining desirable properties for specific functions and applications. Owing to its complex structure and beam-sensitive nature, determining the extent of ion incorporation and its corresponding location in the β-TCP structure is challenging. Further, very few experimental studies have been able to estimate the location of Ag atoms incorporated in a β-TCP structure while considering the associated changes in lattice parameters. Although the incorporation alters the lattice parameters, the alteration is not significant enough for estimating the location of the incorporated Ag atoms. Here, Ag incorporation in a β-TCP structure was evaluated on atomic scale using scanning transmission electron microscopy (STEM). To the best of our knowledge, this is the first report to unambiguously determine the location of the incorporated Ag atoms in the β-TCP structure by comparing
z
-contrast profiles of the Ag and Ca atoms by combining the state-of-art STEM observations and STEM image simulations. The Ag incorporation in the Ca(4) sites of β-TCP, as estimated by the Rietveld refinement, was in good agreement with the high-angle annular dark-field STEM observations and the simulations of the location of Ag atoms for 001 and 010 zone axes.
HAADF-STEM technique is introduced to locate the incorporated antibacterial Ag atoms in beam-sensitive β-TCP structure.
Chromium (Cr) metal has garnered significant attention in alloy systems owing to its exceptional properties, such as a high melting point, low density, and superior oxidation and corrosion ...resistance. However, its processing capabilities are hindered by its high ductile-brittle transition temperature (DBTT). Recently, powder bed fusion-laser beam for metals (PBF-LB/M) has emerged as a promising technique, offering the fabrication of net shapes and precise control over crystallographic texture. Nevertheless, research investigating the mechanism underlying crystallographic texture development in pure Cr via PBF-LB/M still needs to be conducted. This study explored the impact of scan speed on relative density and crystallographic texture. At the optimal scan speed, an increase in grain size attributed to epitaxial growth was observed, resulting in the formation of a cubic texture. Consequently, a reduction in high-angle grain boundaries (HAGB) was achieved, suppressing defects such as cracks and enhancing relative density up to 98.1%. Furthermore, with increasing densification, Vickers hardness also exhibited a corresponding increase. These findings underscore the efficacy of PBF-LB/M for processing metals with high DBTT properties.
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IZUM, KILJ, NUK, PILJ, PNG, SAZU, UL, UM, UPUK
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•Quasi-static compressions of Ti6Al4V novel 2D auxetic lattices fabricated by PBF-EB.•ATC and TLR structures outperformed double DAH lattice structures in SEA.•Residual stresses are ...in the order of DAH > TLR > ATC, inversely correlating with SEAs.•TLR fabricated at high-speed scan exhibited small fluctuations in SEA.
The metal-based 2D auxetic lattice structures hold the potential for multifunctional tasks in aerospace applications. However, the compression response of those manufactured by powder bed fusion process is underexplored. This study proposes a comprehensive comparison of in-plane quasi-static compression performance of 2D auxetic lattice structures, utilizing three designs (anti-tetrachiral (ATC), double arrow-headed (DAH), and tree-like re-entrant (TLR)), manufactured with stiff Ti6Al4V by the electron beam powder bed fusion process (PBF-EB) with various manufacturing speeds. The results revealed unique failure patterns and superior energy absorptions among 2D lattice structures in the literature. TLR design enhanced energy absorption by overcoming failures between DAH columns and exhibited the lowest standard deviations in specific energy absorption (SEA) values (9.75 %–12.62 %). Besides, Kernel average misorientation (KAM) values followed the order of DAH, TLR, and ATC, and inversely correlated with SEA values. ATC structures with the lowest KAM outperformed DAH and TLR by 47.5 % and 6.44 %, respectively. Scan speed variations affected SEA and porosity values differently for each lattice design while exhibiting similar microstructure characteristics. The findings in this study propose a significant contribution to the development of aerospace sandwich structures where harsh environments exist and employment of 2D topologies are required.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZAGLJ, ZRSKP
The biological properties of hydroxyapatite (HA) are significantly influenced by its compositional characteristics especially doping elements and/or Ca/P ratio, which can be altered by precursor ...chemistry. In this study, a group of boronated (B-incorporated) hydroxyapatite (BHA) was synthesized using a precipitation method by setting the Ca/P ratio to the stoichiometric value of HA (1.67), while altering the precursor chemistry by adjusting either (Ca + B)/P (Ca-deficient precursor, BC) or Ca/(P + B) (P-deficient precursor, BP). After heat-treatment, the partial decomposition of the BC was observed, forming tricalcium phosphate as the byproduct, however, the BP showed phase stability at all temperatures. The B-ionic species in the form of (BO2)− and (BO3)3− were incorporated into the HA structure at the (PO4)3− and (OH)− positions, respectively. The incorporation of the B species also facilitated the incorporation of (CO3)2− groups specifically in the BPs. This is the first finding on BHA reporting that preferential (CO3)2− incorporation depends on the precursor chemistry used. As a result, osteoblast adhesion was superior on the BPs compared to pure HA owing to the carbonated structure, increasing cell spreading area. As such, this in vitro study highlighted that the present P-deficient precursor approach for synthesizing BHA improved biocompatibility properties and should, thus, be further considered for the next-generation of improved orthopedic applications.
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•Synthesis of boronated hydroxyapatite from Ca deficient and P-deficient precursors.•Better stability of the HA synthesized from P-deficient precursors at all heat treatment temperatures.•Incorporation of B species into the structure: BO33− ions into PO43− sites and BO2− ions into OH− sites.•HA formula synthesized from P-deficient precursors with superior biocompatibility is Ca10{(PO4)6−x−y(BO3)x(CO3)y}{(OH)2−z+y(BO2)z}.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZAGLJ, ZRSKP
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•Microstructural control utilizing bimodal feature unique to LPBF-built Scalmalloy.•Decreasing track-to-track interval increases the volume fraction of fine grains.•The increased ...volume fraction of fine grains resulted in increased strength.•The resulting product exhibited an excellent strength-ductility balance.
The bimodal microstructure, which comprises ultrafine grains (UFGs) forming along the melt pool boundary and relatively coarse grains inside the melt pool, is a characteristic of the Sc-Zr-modified Al–Mg-based alloy (Scalmalloy) microstructure manufactured using laser powder bed fusion (LPBF). Focusing on this microstructural feature, we investigated the improvement in the mechanical properties of LPBF-fabricated Scalmalloy by tailoring the volume fraction of UFGs. Our approach was to decrease the laser hatch spacing (d) from 0.1 to 0.04 mm, while the volume fraction of UFGs increased from 34.6 ± 0.6 % (d = 0.1 mm) to 59.5 ± 0.5 % (d = 0.06 mm). The tensile yield stress increased from 296 ± 9 (d = 0.1 mm) to 380 ± 6 MPa (d = 0.06 mm), while maintaining a large elongation (14.8 % ± 1.2 %). The yield stress and elongation were superior to those of the cast counterparts by 2.9 and 4.0 times, respectively. In the sample with d = 0.04 mm, pores formed owing to excessive thermal energy input. Additionally, we investigated multiple strengthening mechanisms of the as-fabricated alloy. This is the first study to improve the mechanical properties of LPBF-fabricated Scalmalloy by optimizing the track-to-track interval and tuning the UFG fraction.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZAGLJ, ZRSKP
Additive manufacturing offers an exclusive way of anisotropic microstructure control with a high degree of freedom regarding variation in process parameters. This study demonstrates a unique texture ...formation in Inconel 718 (IN718) using a bidirectional laser scan in a laser powder bed fusion (LPBF) process for tailoring the mechanical properties. We developed three distinctive textures in IN718 using LPBF: a single-crystal-like microstructure (SCM) with a orientation in the build direction (BD), crystallographic lamellar microstructure (CLM) with a -oriented main layer and -oriented sub-layer in the BD, and polycrystalline with a weak orientation. The microstructure observations and finite element simulations showed that the texture evolution of the SCM and CLM was dominated by the melt-pool shape and related heat-flow direction. The specimen with CLM exhibited a simultaneous improvement in strength and ductility owing to the stress-transfer coefficient between the -oriented main and -oriented sub-grains, showing superior mechanical properties compared to cast-IN718. This behavior is largely attributed to the presence of the boundary between the main and sub-layers (crystallographic grain boundary) lying parallel to the BD uniquely formed under the LPBF process. Furthermore, the strength–ductility balance of the part with the CLM can be controlled by changing the stress-transfer coefficient and the Schmidt factor through an alteration of the loading axis. Control of the crystallographic texture, including the CLM formation, is beneficial for tailoring and improving the mechanical performance of the structural materials, which can be a promising methodology.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZAGLJ, ZRSKP
Laser powder bed fusion (LPBF)-manufactured Sc-Zr-modified Al–Mg alloy (Scalmalloy) has a bimodal microstructure comprising coarse grains (CGs) in the hot melt pool area and ultrafine grains (UFGs) ...along the melt pool boundaries (MPBs). Owing to these microstructural features, an increase in the MPBs can increase the UFGs, leading to enhanced mechanical properties. However, the effects of the LPBF process parameters, especially the laser scan strategy, on the microstructure and mechanical properties of Scalmalloy are still unclear. Here, a comparative study was conducted between X- and XY-mode laser scan strategies, with the same volumetric energy, based on the melt pool configuration, grain size distribution, and precipitation behaviors. The X-scan exhibited mechanical properties superior to those exhibited by the XY-scan, attributed to the higher volume fraction (VF) of UFGs. An increase in the VF of UFGs was observed, from 46% for the XY-scan to 56% for the X-scan, owing to an increase in MPBs. Consequently, the tensile strength of the X-scan was higher than that of the XY-scan. The maximum yield strength (271.5 ± 2.7 MPa) was obtained for the X-scan strategy, which was approximately twice that obtained for casting. The results of this study demonstrate that the microstructure and mechanical properties of Scalmalloy can be successfully tuned by a laser scanning strategy.
The 2D double arrow-headed (DAH) lattice structures, which are promising cellular structures for impact mitigation, remain relatively unexplored in terms of their compression response when ...manufactured using the powder bed fusion process with Ti6Al4V (Ti64) alloy. This study aims to investigate the effects of build orientation and beam scan speed of Electron Beam Powder Bed Fusion (PBF-EB) process on the energy absorption of 2D Ti64 DAH lattice structures. Additionally, potential microstructural variations due to adjusted process parameters can be linked to different levels of energy absorption. For the compressions, the lattice structures were manufactured at two build orientations (0° and 45°), using three different beam scan speeds: speed function (SF), low speed (LS), high speed (HS). In micro-characterizations, the unit cells of 0deg-LS exhibited the lowest micro-porosity level at 0.12 %. Based on KAM values, thin struts at unit cells had higher residual stresses than thick struts, contributing to the initiation of failure locations. The compressions revealed that the 0deg-LS group absorbed 21.6 % and 24 % more energy than 0deg-SF and 0deg-HS groups, respectively, at compressions of 33 %. 45° samples absorbed approximately 10 % more energy than 0° samples except HS groups. The lowest micro-porosity of 0deg-LS contributed to having the highest energy absorption among 0deg samples. As the residual stresses in KAM values did not differ strongly with varying beam speed, varied energy absorptions were not linked to them. An optimization of the numerical compressions helped obtain designs with higher energy absorption and less relative volume. This study provides valuable insights into Ti64 cellular applications constrained with 2D-type designs.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZAGLJ, ZRSKP
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