Chinese Journal of Mechanical Engineering: Additive Manufacturing Frontiers最新文献

The unique properties of bulk metallic glass (BMG) render it an excellent material for bone-implant applications. BMG samples are difficult to produce directly because of the critical cooling rate of molding. Advancements in additive manufacturing technologies, such as selective laser melting (SLM), have enabled the development of BMG. The successful production of materials via SLM relies significantly on the processing parameters; meanwhile, the overall energy density affects the crystallization and, thus, the final properties. Therefore, to further determine the effects of the processing parameters, SLM is performed in this study to print Fe-based BMG with different properties three dimensionally using selected processing parameters but a constant energy density. The printed amorphous Fe-based BMG outperforms the typical 316 L stainless steel (316 L SS) in terms of mechanical properties and corrosion resistance. Moreover, observations from nanoindentation tests indicate that the hardness and elastic modulus of the Fe-based BMG can be customized explicitly by adjusting the SLM processing parameters. Indirect cytotoxicity results show that the Fe-based BMG can enhance the viability of SAOS2 cells, as compared with 316 L SS. These intriguing results show that Fe-based BMG should be investigated further for orthopedic implant applications.

Laser powder bed fusion (LPBF) is an innovative method for manufacturing multimaterial components with high geometrical resolution. The LPBF-printing sequences of materials may be diverse in the actual design and application of multimaterial components. In this study, multimaterial copper (CuSn10)–steel (316 L) structures are printed using different building strategies (printing 316 L on CuSn10 and printing CuSn10 on 316 L) via LPBF, and the characteristics of two interfaces (the 316 L/CuSn10 or “L/C” and CuSn10/316 L or “C/L” interfaces) are investigated. Subsequently, the interfacial melting mode and formation mechanisms are discussed. At the L/C interface, the keyhole melting mode induced by the high volumetric energy density (E_L/C = 319.4 J/mm³) results in a large penetration depth in the pre-solidified layer and enhances laser energy absorption, thus promoting the extensive migration of materials and intense intermixing of elements to form a wide diffusion zone (∼400 μm). At the C/L interface, the conduction mode induced by the low volumetric energy density (E_C/L = 74.1 J/mm³) results in a narrow diffusion zone (∼160 μm). The interfacial defects observed are primarily cracks and pores. More cracks appeared at the C/L interface, which is attributable to the weak bonding strength of the narrow diffusion zone. This study provides guidance and reference for the design and manufacturing of multimaterial components via LPBF using different building strategies.

Additive manufacturing (AM) has gained extensive attention and tremendous research due to its advantages of fabricating complex-shaped parts without the need of casting mold. However, distortion is a known issue for many AM technologies, which decreases the precision of as-built parts. Like fusion welding, the local high-energy input generates residual stresses, which can adversely affect the fatigue performance of AM parts. To the best of the authors’ knowledge, a comprehensive review does not exist regarding the distortion and residual stresses dedicated for AM, despite some work has explored the interrelationship between the two. The present review is aimed to fill in the identified knowledge gap, by first describing the evolution of distortion and residual stresses for a range of AM processes, and second assessing their influencing factors. This allows us to elucidate their formation mechanisms from both the micro- and macro-scales. Moreover, approaches which have been successfully adopted to mitigate both the distortion and residual stresses are reviewed. It is anticipated that this review paper opens many opportunities to increase the success rate of AM parts by improving the dimension precision and fatigue life.

The inherent absorption frequency of traditional sound absorbers makes it difficult to solve the problem of acoustic wave removal in a changeable acoustic environment. In this study, acoustic absorption metamaterials (AAMs) with adaptable sound absorption performance were innovatively designed using the structural combination concept and fabricated via 3D printing. Accordingly, two coiled-up channels were combined in a single cell, which could effectively broaden the absorption bandwidth in a limited space. The longitudinal movement of the coiled-up channels endowed the tunable entire depth and internal cavity of the AAMs; thus, the sound absorption performance could be tailored accordingly. Through computational analysis and experimental verification, it was demonstrated that the depth of the AAM could be adjusted from 10 mm to 20 mm, and the corresponding absorption frequencies of the two channels ranged from 206 Hz to 179 Hz and 379 Hz to 298 Hz, respectively. In addition, the finite element results also indicate that the sound absorption bandwidth of AAMs could be further improved by the periodic arrangement of the units. This work opens a promising structural design approach for presenting a route toward acoustic devices with adaptable absorption performances.

Laser welding and laser-based powder-bed fusion additive manufacturing in the deep penetration (keyhole) mode are promising technologies for the synthesis of metal components. The significant potential of these technologies remains latent because of structural defects (porosity), which significantly degrade the structural integrity and performance of the end products. Practical strategies for reducing those defects are addressed through fundamental understanding of their formation. In this study, pore formation of hydrodynamic origin is investigated, including the dynamics and mechanisms of the formation based on the above mentioned technologies. The pore volume and frequency of pore appearance, depending on the amplitude and frequency of capillary vibrations, are considered. Physical analysis is performed to obtain the scanning velocity values for the maximum and zero amplitudes and the frequency of capillary waves. A comparison between calculated curves and experimental data confirms both the capillary origin of the pores and the estimated scanning speeds at which the parameters of the pores exhibit their maximum values or vanish. The results obtained may facilitate in the selection of the optimal scanning speed when designing a pore-free technology.

Hydroxyapatite (HA) bioceramics have garnered considerable attention owing to their applications in the field of bone repair and excellent biocompatibility. Compared to extrusion-based 3D printing, projection-based 3D printing (3DPP) can fabricate parts with complex geometry, high accuracy, and efficiency, which is very promising for bioceramic scaffolds. However, conventional 3DPP using a paste with low viscosity will cause severe shrinkage of the parts after sintering, which makes it unsuitable for bioceramic scaffolds, and a system investigation of the printing process remains insufficient. In this study, we proposed a 3DPP device suitable for bioceramic scaffolds and investigated the additive manufacturing of HA scaffolds. Ceramic paste properties and process parameters of curing, debinding, and sintering were initially examined. The mechanical properties, shrinkage, and biocompatibility in vitro of the sintered samples were further investigated. The obtained results indicate that HA bioceramics with uniform morphology, complex structure, and high accuracy can be manufactured using the 3DPP equipment. HA scaffolds have the mechanical strength of human cancellous bone, while HA scaffolds cultured with osteoblast precursor cells possess strong biocompatibility and can promote osteoblast adhesion, proliferation, and differentiation. These results suggest a promising application of the 3DPP technique in the preparation of bioceramic scaffolds, and the HA scaffolds fabricated using the 3DPP technique exhibit promising potential in fulfilling a constructive role in the biomedical field of human bone regeneration repair.

Zn is a promising biodegradable metal owing to its moderate degradation rate and acceptable biocompatibility. However, the insufficient mechanical strength and plasticity of pure Zn limits its application in bone implants. In this study, a spiral eutectic structure is constructed in Zn–Mg–Ag alloys prepared via selective laser melting to improve their mechanical properties. Results show that the prepared Zn–Mg–Ag alloys are composed of a primary Zn matrix and a eutectic phase, which is composed of alternating α-Zn and an intermetallic compound, MgZn₂. Moreover, the eutectic phase resembles a spiral and increases with Ag content in the alloys. The eutectic pinning effect hinders dislocation and hence results in dislocation accumulation. Meanwhile, the spiral structure alters the propagation direction and dissipates the propagation energy of cracks layer by layer. Consequently, a compressive strength of up to 309 ± 15 MPa and an improved strain of 27% are exhibited in Zn–3Mg–1Ag alloy. Moreover, the Zn–Mg–Ag alloys show high biocompatibility with MG-63 cells and antibacterial activity against Escherichia coli. These findings indicate the potential of spiral eutectic structures for enhancing both the mechanical strength and plasticity of biodegradable Zn alloys.

Increasing lung diseases, mutating coronaviruses, and the development of new compounds urgently require biomimetic in vitro lung models for lung pathology, toxicology, and pharmacology. The current construction strategies for lung models mainly include animal models, 2D cell culture, lung-on-a-chip, and lung organoids. However, current models face difficulties in reproducing in vivo-like alveolar size and vesicle-like structures, and are unable to contain multiple cell types. In this study, a strategy for constructing alveolar models based on degradable hydrogel microspheres is proposed. Hydrogel microspheres, 200–250 µm in diameter, were prepared using a self-developed printing technique driven by alternating viscous and inertial forces. Microcapsules were further constructed using a coacervation-based layer-by-layer technique and core liquefaction. Three types of cells were inoculated and co-cultured on hydrogel capsules based on optimized microcapsule surface treatment strategies. Finally, an in vitro three-dimensional endothelial alveolar model with a multicellular composition and vesicle-like structure with a diameter of approximately 230 µm was successfully constructed. Cells in the constructed alveolar model maintained a high survival rate. The LD₅₀ values of glutaraldehyde based on the constructed models were in good agreement with the reference values, validating the potential of the model for future toxicant and drug detection.