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Anisotropic porous boron carbide (B4C) structures were successfully produced, for the first time, using the magnetic field-assisted freeze casting method. The effect of the magnetic field on the structure and mechanical strength of the formed porous B4C was compared for two different magnetic field directions that were either aligned with ice growth (vertical), or perpendicular to the ice growth direction (horizontal). It was shown that applying even a weak horizontal magnetic field of 0.1–0.3 T noticeably affected the alignment of mineral bridges between lamellar walls. Both the porosity and the channel widths decreased with increasing horizontal magnetic field strength. In the case of a vertical magnetic field, a larger strength of 0.4 T was required for highly aligned lamellar walls and larger channel widths. Compression strength tests indicated that the application of magnetic fields led to more homogeneously aligned channels, which resulted in increased compression strength in the longitudinal (parallel to the ice growth) direction. Applying a vertical magnetic field of 0.4 T with a cooling rate of 2 °C/min during the freezing step of the magnetic field-assisted freeze-casting method was found to result in the best conditions for producing highly anisotropic structures with large channel widths and fewer mineral bridges, which led to an increase in the mechanical strength.

Al/Al2O3 metal matrix composites (MMCs) were produced by metal infiltration of porous ceramic preforms. The porous ceramic preforms were fabricated using the magnetic field-assisted freeze-casting method, resulting in vertically aligned porous channels. Preforms were prepared by freezing an Al2O3/Fe3O4-containing slurry within an applied magnetic field. Vertical alignment of the channels was facilitated by the magnetic response of the Fe3O4 in the slurry during the freezing process. After freezing and sublimation, the ceramic preforms were sintered and then infiltrated with molten A356 Al-based alloy. The mechanical properties of the resulting Al2O3/A356 MMCs were compared to those of bulk Al2O3, bulk Al-based alloy (A356), and porous Al2O3 preforms using micro-indentation testing. The indentation hardness and elastic moduli values of Al2O3/A356 MMCs showed good agreement with the predicted theoretical calculations. This study provides a new approach for the design of MMCs with controlled composition and improved mechanical characteristics.

Magnetic field-assisted freeze-casting of porous alumina structures is reported. Different freeze-casting parameters were investigated and include the composition of the original slurry (Fe3O4 and PVA content) and the control of temperature during the free casting process. The optimum content of the additives in the slurry were 3 and 6 wt% for PVA and Fe3O4, respectively. These conditions provided the most unidirectional porous structures throughout the length of the sample. The sintering temperature was maintained at 1500 °C for 3 h. The application of a vertical magnetic field (parallel to ice growth direction) with using a cooling rate mode technique was found to enhance the homogeneity of the porous structure across the sample. The current study suggests that magnetic field-assisted freeze-casting is a viable method to create highly anisotropic porous ceramic structures.

Here, we present a new combined freeze-casting and laser processing method for the design of yttria-stabilized zirconia (YSZ) based thermal-barrier coatings. YSZ ceramics with unidirectionally-aligned pore channels were created using the freeze-casting method. After sintering, top view and cross-sectional scanning electron microscopy (SEM) revealed the structural features of the preform, which exhibits a 74 ± 2% volume fraction of porosity and an average pore channel size of 30 ± 3 μm. The measured thermal conductivity of this porous structure was 0.27 ± 0.02 W/(m K), which is eight times lower than that of reported values for dense YSZ. Though high porosity is beneficial both from a structural and thermal response perspective, the open porosity could potentially be an issue from an application stand-point when evaluating the resistance of materials to calcium–magnesium–aluminum–silicon oxide (CMAS) attack. CMAS attack, which can originate from deposits of molten sand, ash, and dust, is one of the major causes of thermal barrier coating failure. Therefore, the surface of the porous samples was modified using a laser process to create a barrier to CMAS infiltration. SEM micrographs aided in determining the optimum laser parameters required to fully seal the surface using a laser treatment. The performance of the original porous and surface-modified YSZ was compared by conducting CMAS infiltration studies. Laser modification was shown to be a viable technique to significantly reduce CMAS infiltration in porous thermal barrier coatings.

TNZT alloys such as Ti-35Nb-7Zr-5Ta exhibit better biocompatibility than the more widely used Ti-6Al-4V alloy. Furthermore, TNZT alloys typically have lower Young's moduli (50–60 GPa) than most Ti-based alloys. A low modulus allows for a greater transfer of functional loads since it is much closer to the modulus of bone, which ultimately leads to more growth and support from natural bone. TNZT alloys were produced by vacuum arc melting of pure elements that were subsequently rolled to sheet. Oxide nano-scaffolds were grown on TNZT samples using a hydrothermal treatment in 40 mL sodium hydroxide solution at 60 °C using either 0.5 or 5.0 M concentrations, with and without TiO2 nanoparticles, for either 24 or 48 h to create nanostructured surfaces to help improve osseointegration. The alloys with and without nano-scaffolds were characterized using top-view and cross-sectional scanning electron microscopy equipped with an energy dispersive x-ray spectrometer to investigate the structure, morphology, and chemistry of the resulting nanostructures. Nano-scaffolds were found to grow for a sodium hydroxide concentration of 5.0 M regardless of the treatment time (24 to 48 h). A pore size of 60 nm and 80 nm were observed for samples treated for 24 and 48 h, respectively. No porous structures were observed for samples produced for a sodium hydroxide solution of 0.5 M or with TiO2 nanoparticles.

Search for low-moment magnetic materials with high spin-polarization is important for emerging spintronics applications. In this work, we have conducted detailed growth and characterization along with complementary first-principles calculations to investigate the structure and magnetism of Mn2FeSi, which is a prospective inverse-Heusler material. We confirm that Mn2FeSi adopts a cubic inverse-Heusler structure, in excellent agreement with theory. The magnetic and resistivity measurements show an antiferromagnetic behavior with a Neel temperature of 48 K, which is consistent with prior experimental reports. We find that a low-moment state with higher ordering temperature (150–200 K) can be stabilized under certain growth conditions. Supporting calculations show that Neel-type antiferromagnetic states are energetically very close to the ferrimagnetic ground state. Our work provides evidence that Mn2FeSi may be interesting for exploring newer applications with low-moment materials, but the ordering temperatures are low for viable practical applications.