Materialia最新文献

The possibility to realize Additively Manufactured functionally graded lattice structure based on Voronoi tessellation enormously increases the possibility in tailoring the stiffness, mechanical properties and energy absorption capacity of the samples. The work presents the design and mechanical characterization of functionally thickness graded Voronoi lattice structures in comparison with constant thickness lattice structures for the evaluation of mechanical performance and energy absorption capacity. Firstly, the design and laser power bed fusion process are detailed. The dimensional deviation between designed models and Ti6Al4V specimens is quantified to assess the samples’ quality. Their mechanical performance is analyzed by quasi-static compression experimental tests, supported by numerical analysis for the evaluation of local stress distributions and deformation modes. The average dimensional deviation between CAD models and fabricated samples is 0.09 mm, likeminded with the literature optimum. The structures exhibit Young Modulus values ranging between 10 MPa and 21 MPa, compatible with biomedical applications. The compressive force for thickness graded structures tends to increase up to densification, while uniform thickness structures present an almost constant value of force in the platform stage. Additionally, the energy storage changes according to the presence of thickness gradient: the larger the thickness gradient, the larger the energy absorption capacity.

In powder-based additive manufacturing (AM), the quality of the feedstock material is critical for obtaining enhanced mechanical properties. Recently, the application of coated powders during directed energy deposition (DED) has been prompted by the goal of fabricating composite and functional materials in-situ. The complex temperature and momentum fields established during DED render direct experimental characterization of coated powder behavior challenging. To address this challenge, this study reports on the thermal behavior of coated powders during interactions with the molten pool by constructing three-dimensional heat transfer and phase distribution models using the finite elements method (FEM). Transient temperature and phase distributions were calculated for coated and uncoated stainless steel 316L and ZnAl powders under various particle size, coating thickness, molten pool temperature, and coating material conditions. Particle residence time values were extracted from the calculations, defined as time spent by the particle before a phase change. The results show large variations in particle residence time (85 μs to 2670 μs for stainless steel 316L particles, and 48 μs to infinity for ZnAl particles) as a function of the variables considered, especially the thermal diffusivity of the coating materials, thereby highlighting the potential value of coatings as an additional design parameter in DED. Significant increases in particle residence time for both stainless steel 316L and ZnAl particles were found when contact angle increases from 0° (submergence regime) to 180° (floating regime).

This study evaluates the compressive properties of stereolithography (SLA) fabricated open-cell lattices, specifically triply periodic minimal surface (TPMS) gyroid and stochastic structures, for artificial bone applications. Two resins, Standard White and BioMed Amber, were tested across four relative densities (0.2, 0.3, 0.4, 0.5). Mechanical characterization of horse tuber coxae trabecular bone used as a biological comparator showed an average elastic modulus of 0.05 GPa and a yield strength of 3.369 MPa. Gyroid structures exhibited higher elastic modulus and yield strengths, with BioMed Amber gyroid at a density of 0.5, achieving an elastic modulus of 0.623 GPa and yield strength of 14.149 MPa. Stochastic structures showed lower and more variable mechanical properties. The highest yield strength for stochastic structures was observed in BioMed Amber at a density of 0.5 (14.199 MPa). Comparative analysis indicated that high-performing synthetic structures approach the lower bounds of natural bone properties. Using a field-driven design approach, variable relative density structures were developed to emulate the mechanical properties of natural bone. SEM analysis provided insights into failure mechanisms, highlighting the impact of relative density on structural integrity and material ductility. This research supports the development of 3D-printed bone-like structures as viable substitutes for cadaveric specimens in preclinical tests, with implications for material science and orthopedic applications.

Laser powder-bed fusion (LPBF) processed Nb-based alloy C103 (Nb-10Hf-1Ti wt.%) develops a complex, hierarchical microstructure comprising a fine-scale solidification cell structure, overlaid with a dense dislocation-network outlining the cell boundaries, within the primary grains. Additionally, sub-grain boundaries and a fine-scale dispersion of nano-sized hafnium oxide precipitates, possibly forming during solidification, decorate the solidification cell boundaries as well as exist within the cells. This complex hierarchical microstructure results in impressive tensile mechanical properties. Post-build stress-relieving annealing and hot isostatic pressing (HIP) largely annihilates the solidification cell structure and associated dislocation network, lowering the strength but with substantial recovery of tensile ductility. Nevertheless, the resulting microstructure offers higher strengths as compared to their wrought counterparts.

The properties of materials in irradiation environments are significantly influenced by hydrogen and helium. However, the effects of gas-dose ratio on the evolution of defects, which are crucial for material application assessment in various nuclear reactors and for understanding fundamental irradiation mechanisms, remain unclear. In this paper, defect evolution within pure iron was investigated in-situ through simultaneous triple-beam irradiation at 723 K using 400 keV Fe⁺, 50 keV He⁺ and 50 keV H₂⁺. Four different gas-dose ratios were used: 10 appm He/dpa & 45 appm H/dpa, 10 appm He/dpa & 100 appm H/dpa, 100 appm He/dpa & 100 appm H/dpa, and 45 appm He/dpa & 10 appm H/dpa. It was observed that the gas-dose ratio significantly influenced the evolution of defects, including the size and density of dislocation loops and bubbles. It was found that an increased hydrogen-dose ratio, when paired with a constant helium-dose ratio, resulted in smaller loop sizes, but increased the density of loops and bubbles. Conversely, maintaining a constant hydrogen dose ratio while increasing the helium dose ratio proved advantageous for raising the density of loops and bubbles, and for reducing loop size. Additionally, an increase in both hydrogen and helium-dose ratios was associated with heightened swelling due to bubble formation. Moreover, hydrogen was found to have a less impact on loop nucleation compared to helium, and helium exhibited a more pronounced inhibitory effect on loop migration than hydrogen.

Translucent persistent luminescence glass matrix composites (PeL-GMCs) were successfully obtained for the first time using a pressureless viscous sintering method with silicate glass as the host material. Initially, persistent luminescence microparticles (PeL-MPs) of SrAl₂O₄: Eu²⁺; Dy³⁺ were prepared by microwave-assisted synthesis under a reducing atmosphere. To obtain persistent luminescent glass matrix composites, 1 wt. % of these particles were mixed with soda-lime-silicate glass beads and pressed into pellets. Subsequently, the disk-shaped samples were heat-treated through pressureless viscous sintering. Despite some material porosity, the PeL-GMCs exhibited translucency and prolonged persistent luminescence $\left(\sim 12min\right)$. Additionally, we noted excellent compatibility between the PeL-MPs and the glass host, since no chemical interaction was found, as verified by optical microscopy, energy dispersive X-ray (EDX) mapping analysis and cathodoluminescence (CL) in SEM. Furthermore, the afterglow intensity of the particles was maintained after the preparation of materials.

Sulfur is considered an unfavorable element in metallic materials because of its potential to cause embrittlement, thereby prompting its removal. However, trace amounts of S impurities can influence the precipitation of the primary α-Cr strengthening phase in the heat-resistant 50Ni–30Cr–0.8Ti–6W–Fe alloy, and thus affect its creep strength. In this study, fine Ti₂S particles were observed in heat-treated 50Ni–30Cr–0.8Ti–6W–Fe alloys through high-sensitivity, high-resolution, and wide-field element analysis using aberration-corrected scanning transmission electron microscopy. The Ti₂S particles were distributed linearly with the adjacent α-Cr precipitates. The Ti₂S precipitates functioned as nucleation sites for α-Cr, thereby refining and increasing the hardness of the alloy. The findings of this work challenge conventional approaches to material design and emphasize the significance of design based on fundamental principles.

This study entails the fabrication of two oxide-dispersion strengthened (ODS) Hastelloy-N (HN) alloys utilizing divergent methods. The first alloy was synthesized using cryogenic attritor milling coupled with spark plasma sintering (SPS), while the second was produced via room temperature attritor milling and SPS. The ODS HN alloy derived from cryogenic milling demonstrated superior strength relative to its commercial-grade counterpart. Conversely, the alloy produced through room temperature milling exhibited lower ultimate tensile strength (UTS), attributed to manufacturing defects and the precipitation of Zr at grain boundaries. Corrosion resistance in molten FLiNaK for both ODS samples was found to be inferior compared to commercial HN. Particularly, in the room temperature-milled ODS HN, Zr present at grain boundaries appeared to dissolve more readily than in cryogenic or commercial samples, facilitating enhanced penetration by molten salt. The cryogenically-milled ODS HN contained Zr, yet it was not segregated to grain boundaries. Although the homogeneously dispersed Mo-based compound in the cryogenically-milled ODS HN augmented mechanical properties, it also accelerated corrosion propagation beyond that of the commercial-grade alloy.

Reactive spark plasma sintering of ternary Ti-Si-C system was performed using three different powder precursors systems 3Ti/Si/2C, 3Ti/SiC/C and 2Ti/TiC/Si, to explore the fundamental physics behind Ti₃SiC₂ MAX phase formation, its stability and microstructure development, and, finally linked with its hardening and contact induced damage tolerance. Phase evolution in Ti-Si-C system is a complex phenomenon, and, present experimental conditions never yield a phase pure Ti₃SiC₂ MAX phase, rather results in varying volume fractions of Ti₃SiC₂-(Ti_x,Si_1-x)C solid solution due to non-equilibrium processing conditions exerted by SPS processing which restricts coherent site specific diffusional jumps and promotes the formation of (Ti, Si)C solid-solution instead of well reported non-stoichiometric TiC_x. 3Ti/SiC/C precursor was the best candidate for processing composite with highest yields of Ti₃SiC₂. Phase evolution is guided by the free energy of formation of different phases and chemical affinity amongst the constituent elements rather than the equilibrium phase diagram of the Ti-Si-C system. Presence of free carbon, low temperature liquid phase and slow heating rate are the key requirements for forming phase pure Ti₃SiC₂, where excess free carbon reduces the stability of Ti₃SiC₂ via decarburization. Non-equilibrium processing conditions impart nano-precipitation of coherent hexagonal Ti₃SiC₂ precipitates within a cubic (Ti, Si)C matrix with a distinct orientation relation of (220)_matrix ║(0004)_precipitate and <114>_matrix ║<2–1–10>_precipitate that has never been reported, instead of growing highest density plane of hcp-on-fcc matrix. Coherency strain and fine interlocking microstructure of the as-processed composite experiences ≈36 % of enhancement in hardness followed by an improved contact damage for the as-processed composite.