Ultrauniform, strong, and ductile 3D-printed titanium alloy through bifunctional alloy design.

Coarse columnar grains and heterogeneously distributed phases commonly form in metallic alloys produced by three-dimensional (3D) printing and are often considered undesirable because they can impart nonuniform and inferior mechanical properties. We demonstrate a design strategy to unlock consistent and enhanced properties directly from 3D printing. Using Ti-5Al-5Mo-5V-3Cr as a model alloy, we show that adding molybdenum (Mo) nanoparticles promotes grain refinement during solidification and suppresses the formation of phase heterogeneities during solid-state thermal cycling. The microstructural change because of the bifunctional additive results in uniform mechanical properties and simultaneous enhancement of both strength and ductility. We demonstrate how this alloy can be modified by a single component to address unfavorable microstructures, providing a pathway to achieve desirable mechanical characteristics directly from 3D printing.

Fabrication and Properties of Biodegradable Akermanite-Reinforced Fe35Mn Alloys for Temporary Orthopedic Implant Applications.

As a representative of the biodegradable iron (Fe)-manganese (Mn) alloys, Fe35Mn has been investigated as a promising biodegradable metal biomaterial for orthopedic applications. However, its slow degradation rate, though better than pure Fe, and poor bioactivity are concerns that retard its clinical applications. Akermanite (Ca2MgSi2O7, Ake) is a silicate-based bioceramic, showing desirable degradability and bioactivity for bone repair. In the present work, Fe35Mn/Ake composites were prepared via a powder metallurgy route. The effect of different contents of Ake (0, 10, 30, 50 vol %) on the microstructure, mechanical properties, degradation, and biocompatibility of the composites was investigated. The ceramic phases were found to be evenly distributed in the metal matrix. The Ake reacted with Fe35Mn and generated CaFeSiO4 during sintering. The addition of Ake increased the relative density of pure Fe35Mn from ∼90 to ∼94-97%. The compressive yield strength (CYS) and elastic modulus (Ec) increased with increasing Ake, with Fe35Mn/50Ake exhibiting the highest CYS of ∼403 MPa and Ec of ∼18 GPa. However, the ductility decreased at higher Ake concentrations (30 and 50%). Microhardness also showed an increasing trend with the addition of Ake. Electrochemical measurements indicated that higher concentrations of Ake (30 and 50%) could potentially increase the corrosion rate of Fe35Mn from ∼0.25 to ∼0.39 mm/year. However, all of the compositions tested did not show measurable weight loss after immersion in simulated body fluid (SBF) for 4 weeks, attributed to the use of prealloyed raw material, high sintered density of the fabricated composites, and the formation of a dense Ca-, P-, and O-rich layer on the surface. Human osteoblasts on Fe35Mn/Ake composites showed increasing viability with increasing Ake content, indicating improved in vitro biocompatibility. These preliminary results suggest that Fe35Mn/Ake can be a potential material for biodegradable bone implant applications, particularly Fe35Mn/30Ake, if the slow corrosion of the composite can be addressed.

In Situ Observation of Liquid Solder Alloys and Solid Substrate Reactions Using High-Voltage Transmission Electron Microscopy.

The complex reaction between liquid solder alloys and solid substrates has been studied ex-situ in a few studies, utilizing creative setups to "freeze" the reactions at different stages during the reflow soldering process. However, full understanding of the dynamics of the process is difficult due to the lack of direct observation at micro- and nano-meter resolutions. In this study, high voltage transmission electron microscopy (HV-TEM) is employed to observe the morphological changes that occur in Cu6Sn5 between a Sn-3.0 wt%Ag-0.5 wt%Cu (SAC305) solder alloy and a Cu substrate in situ at temperatures above the solidus of the alloy. This enables the continuous surveillance of rapid grain boundary movements of Cu6Sn5 during soldering and increases the fundamental understanding of reaction mechanisms in solder solid/liquid interfaces.

Mechanical properties and biocompatibility of porous titanium scaffolds for bone tissue engineering.

Synthetic scaffolds are a highly promising new approach to replace both autografts and allografts to repair and remodel damaged bone tissue. Biocompatible porous titanium scaffold was manufactured through a powder metallurgy approach. Magnesium powder was used as space holder material which was compacted with titanium powder and removed during sintering. Evaluation of the porosity and mechanical properties showed a high level of compatibility with human cortical bone. Interconnectivity between pores is higher than 95% for porosity as low as 30%. The elastic moduli are 44.2GPa, 24.7GPa and 15.4GPa for 30%, 40% and 50% porosity samples which match well to that of natural bone (4-30GPa). The yield strengths for 30% and 40% porosity samples of 221.7MPa and 117MPa are superior to that of human cortical bone (130-180MPa). In-vitro cell culture tests on the scaffold samples using Human Mesenchymal Stem Cells (hMSCs) demonstrated their biocompatibility and indicated osseointegration potential. The scaffolds allowed cells to adhere and spread both on the surface and inside the pore structures. With increasing levels of porosity/interconnectivity, improved cell proliferation is obtained within the pores. It is concluded that samples with 30% porosity exhibit the best biocompatibility. The results suggest that porous titanium scaffolds generated using this manufacturing route have excellent potential for hard tissue engineering applications.

Structural studies of group 1 metal 4-azapentalenyl complexes.

The first structurally authenticated 4-azapentalenyl complexes are reported, along with DFT studies, that reveal tendencies for their cyclopentadienyl isostructural nature and an ability to exhibit binding modes of varying hapticity.