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An advantage of the powder-bed-based metal additive manufacturing (AM) processes is that the powder can be reused. The powder reuse or recycling times directly affect the affordability of the additively manufactured parts, especially for the AM of titanium parts. This study examines the influence of powder reuse times on the characteristics of Ti-6Al-4V powder, including powder composition, particle size distribution (PSD), apparent density, tap density, flowability, and particle morphology. In addition, tensile samples were manufactured and evaluated with respect to powder reuse times and sample locations in the powder bed. The following findings were made from reusing the same batch of powder 21 times for AM by selective electron beam melting: (i) the oxygen (O) content increased progressively with increasing reuse times but both the Al content and the V content remained generally stable (a small decrease only); (ii) the powder became less spherical with increasing reuse times and some particles showed noticeable distortion and rough surfaces after being reused 16 times; (iii) the PSD became narrower and few satellite particles were observed after 11 times of reuse; (iv) reused powder showed improved flowability; and (v) reused powder showed no measurable undesired influence on the AM process and the samples exhibited highly consistent tensile properties, irrespective of their locations in the powder bed. The implications of these findings were discussed.

An array of eight long Ti-6Al-4V rods (diameter: 12 mm; height: 300 mm) have been additively manufactured, vertically and perpendicular to the powder bed, by selective electron beam melting (SEBM). The purpose was to identify and understand the challenges of fabricating Ti-6Al-4V samples or parts from a deep powder bed (more than 200-mm deep) by SEBM and the necessity of applying post heat treatment. The resulting microstructure and mechanical properties of these Ti-6Al-4V rods were characterized along their building ( i.e., axial) direction by dividing each rod into three segments (top, middle, and bottom), both before ( i.e., as-built) and after hot isostatic pressing (HIP). The as-built microstructure of each rod was inhomogeneous; it was coarsest in the top segment, which showed a near equilibrium α - β lamellar structure, and finest in the bottom segment, which featured a non-equilibrium mixed structure. The tensile properties varied along the rod axis, especially the ductility, but all tensile properties met the requirements specified by ASTM F3001-14. HIP increased the relative density from 99.03 pct of the theoretical density (TD) to 99.90 pct TD and homogenized the microstructure thereby leading to highly consistent tensile properties along the rod axis. The temperature of the stainless steel substrate used in the powder bed was monitored. The as-built inhomogeneous microstructure is attributed to the temperature gradient in the deep powder bed. Post heat treatment is thus necessary for Ti-6Al-4V samples or parts manufactured from a deep powder bed by SEBM. This differs from the additive manufacturing of small samples or parts from a shallow powder bed (less than 100-mm deep) by SEBM.

The capabilities of metal additive manufacturing (AM) are evolving rapidly thanks to both increasing industry demand and improved scientific understanding of the process. This article provides an overview of AM of the Ti-6Al-4V alloy, which has essentially been used as a yardstick to gauge the capability of each metal AM process developed to date. It begins by summarizing the metal AM processes existing today. This is followed by a discussion of the macro- and microstructural characteristics, defects, and tensile and fatigue properties of AM Ti-6Al-4V by selective laser melting, laser metal deposition (both powder and wire), and selective electron-beam melting compared to non-AM Ti-6Al-4V. The tensile and fatigue properties of as-built AM Ti-6Al-4V (with machined or polished surfaces) can be made comparable, or even superior, to those of Ti-6Al-4V in the most commonly used mill-annealed condition. However, these properties can exhibit a large degree of scatter and are often anisotropic, affected by AM build orientations. Post-AM surface treatments or both the post-AM surface and heat treatments are necessary to ensure the minimum required properties and performance consistency. Future directions to further unlock the potential of AM of Ti-6Al-4V for superior and consistent mechanical properties are also discussed.

Sheet (0.41–4.80 mm thick) or thin plate structures commonly exist in additively manufactured Ti-6Al-4V components for load-bearing applications. A batch of 64 Ti-6Al-4V sheet samples with dimensions of 210/180 mm × 42 mm × 3 mm have been additively manufactured by selective electron beam melting (SEBM). A comprehensive assessment was then made of their density, surface flatness, microstructure, and mechanical properties in both as-built and hot isostatically pressed conditions, including the influence of the hot isostatic pressing (HIP) temperature. In particular, standard long tensile (156 mm long, 2 mm thick) and fatigue (206 mm long, 2 mm thick) test sheet samples were used for assessment. As-built SEBM Ti-6Al-4V sheet samples with machined surfaces fully satisfied the minimum tensile property requirements for mill-annealed TIMETAL Ti-6Al-4V sheet products, whereas HIP-processed samples (2 mm thick) with machined surfaces achieved a high cycle fatigue (HCF) strength of 625 MPa (R = 0.06, 10 7 cycles), similar to mill-annealed Ti-6Al-4V (500–700 MPa). The unflatness was limited to 0.2 mm in both the as-built and HIP-processed conditions. A range of other revealing observations was discussed for the additive manufacturing of the Ti-6Al-4V sheet structures.

Bin Tean Teh and colleagues report the genomic characterization of 100 breast fibroepithelial tumors, including benign fibroadenomas and benign, borderline and malignant phyllodes tumors. They identify mutations specific to phyllodes tumors and find somatic mutation patterns that distinguish borderline and malignant phyllodes tumors from the other tumor types. Breast fibroepithelial tumors comprise a heterogeneous spectrum of pathological entities, from benign fibroadenomas to malignant phyllodes tumors 1 . Although MED12 mutations have been frequently found in fibroadenomas and phyllodes tumors 2 , 3 , 4 , 5 , 6 , 7 , the landscapes of genetic alterations across the fibroepithelial tumor spectrum remain unclear. Here, by performing exome sequencing of 22 phyllodes tumors followed by targeted sequencing of 100 breast fibroepithelial tumors, we observed three distinct somatic mutation patterns. First, we frequently observed MED12 and RARA mutations in both fibroadenomas and phyllodes tumors, emphasizing the importance of these mutations in fibroepithelial tumorigenesis. Second, phyllodes tumors exhibited mutations in FLNA , SETD2 and KMT2D , suggesting a role in driving phyllodes tumor development. Third, borderline and malignant phyllodes tumors harbored additional mutations in cancer-associated genes. RARA mutations exhibited clustering in the portion of the gene encoding the ligand-binding domain, functionally suppressed RARA-mediated transcriptional activation and enhanced RARA interactions with transcriptional co-repressors. This study provides insights into the molecular pathogenesis of breast fibroepithelial tumors, with potential clinical implications.

To optimize the antidepressant efficacy of repetitive transcranial magnetic stimulation (rTMS), it is important to examine the impact of brain state during therapeutic rTMS. Evidence suggests that brain state can modulate the brain’s response to stimulation, potentially diminishing antidepressant efficacy if left uncontrolled or enhancing it with inexpensive psychological or other non-pharmacological methods. Thus, we conducted a PRISMA-ScR-based scoping review to pool studies administering rTMS with psychological and other non-pharmacological methods. PubMed and Web of Science databases were searched from inception to 10 July 2024. Inclusion criteria: neuropsychiatric patients underwent rTMS; studies assessed depressive symptom severity; non-pharmacological tasks or interventions were administered during rTMS, or did not include a wash-out period. Of 8,442 studies, 20 combined rTMS with aerobic exercise, bright light therapy, cognitive training or reactivation, psychotherapy, sleep deprivation, or a psychophysical task. Meta-analyses using random effects models were conducted based on change scores on standardized scales. The effect size was large and therapeutic for uncontrolled pretest-posttest comparisons (17 studies, Hedges’ g = −1.91, (standard error) SE = 0.45, 95% (confidence interval) CI = −2.80 to −1.03, p < 0.01); medium when studies compared active combinations with sham rTMS plus active non-pharmacological methods (8 studies, g = −0.55, SE = 0.14, 95% CI = −0.82 to −0.28, p < 0.01); and non-significant when active combinations were compared with active rTMS plus sham psychological methods (4 studies, p = 0.96). Attempts to administer rTMS with non-pharmacological methods show promise but have not yet outperformed rTMS alone.

In order to optimize the processing parameters of a new low-cost titanium alloy connecting rod made of powder forging, the deformation behavior of an α + β type Ti–1.5Fe–2.25Mo (wt%) alloy produced by elemental powder metallurgy (PM) route was studied using isothermal compression tests. The constitutive equations and a processing map were established to characterize the flow behavior and predict the optimum deformation parameters. The calculated apparent activation energy was 257.73 kJ/mol for deformation in the α + β phase region and 378.01 kJ/mol in the β phase region. Two deformation mechanism domains were found: α + β → β phase transformation and dynamic recrystallization. The results show that the optimum deformation parameters for the present alloy are (700–800 °C, 10 −1.7 –1 s −1 ) and (800–900 °C, 10 −2 –10 s −1 ). Based on these results, a finite element method (FEM) simulation of the hot-forming of a connecting rod was conducted, and the simulated results have been successfully used in an industrial forging of the connecting rod.

Tantalum is a refractory metal with a melting point of 2996°C but it offers outstanding biocompatibility for bone implant applications. In this study, the selective electron beam melting (SEBM) process was used for the first time to fabricate both dense and fine lattice tantalum structures. The use of 90-ppm-oxygen Ta powder for SEBM ensured excellent ductility of the as-printed fine Ta lattice implants with strut diameter of just 350 μm. The as-printed dense Ta samples (99.90%) achieved tensile ductility of 45% compared with the minimum requirement of 25% by ISO 13782 and the reported 2% fabricated by SLM using 1800-ppm-oxygen Ta powder. Since 2016, 27 clinical applications have been achieved in China using the custom-designed and SEBM-printed Ta implants by the authors of this study. All these Ta implants (mostly Ta lattice structures) have performed satisfactorily in patients’ bodies so far. Three selected clinical applications, Ta lattice hip, fibula and femur implants, are briefly discussed in this article.

Intricate metal lattice structures enabled by additive manufacturing (AM) are finding increasing applications. We report a detailed study of the manufacturability of Ti-6Al-4V lattice struts by selective electron beam manufacturing (SEBM). A total of 165 strut samples with design diameters of 0.05–3.0 mm are manufactured at 11 different inclination angles from 0° to 90°. The discrepancies between the design and manufactured diameters and the surface roughness and 3D internal defect features of the strut samples are characterized in detail and discussed. Essential research data are produced for the design and manufacture of quality Ti-6Al-4V struts for lattice design by SEBM.

Additively manufactured Ti-6Al-4V lattices have found important applications but their mechanical properties remain insufficient, compared with light alloys of similar densities. This study investigates the influence of chemical etching, hot isostatic pressing (HIP) and β-annealing on the ductility and strength of selective electron beam melted Ti-6Al-4V lattices. We show that applying β-annealing substantially increased the ductility of Ti-6Al-4V cubic lattices from 8.76% to 32.88% and strength from 194.56 to 321.98 MPa, due to the improved microstructure, which eliminated premature fracture of lattice struts and allowed for significant lattice densification. In contrast, although HIP closed strut internal porosity, it only marginally improved the lattice ductility and strength, much less comparable to β-annealing. Chemical etching worsened the lattice mechanical properties, attributed to the extra dents left after particle removal. Stress fluctuation was common in the stress–strain curve for as-printed, chemically etched and HIP-processed lattices but absent for β-annealed lattices, which exhibited smooth and stable stress–strain curves.