Magnetic field-assisted freeze-casting was used to create porous B4C ceramic preforms. An optimum slurry consisted of a mixture of B4C powders and 6-wt

Additive friction stir deposition (AFSD), a deformation-based, near-net-shaping additive technology, is used to consolidate Al chips from automotive castings to produce fully-dense components, while addressing the energy, environmental, and efficiency challenges associated with recycling these chips via melting. Cold pressing of the chips results in feed-rods with a relative density of 68%. AFSD of these porous feed-rods leads to porosity-free material in the as-printed state. Compared to the base material of bulk cast Al, the as-printed material increases the tensile elongation from less than 1% to 17.8%, while exhibiting significant strain hardening. This upcycling effect is shown to originate from microstructure evolution during deposition, including the second-phase particles and the grain structure. The received Al chips have a hypereutectic composition and thus contain a high proportion of primary Si particles. The minor presence of Fe causes additional intermetallic particles as well. After deposition, these Si and Fe-based particles are refined, spherodized, and uniformly distributed in the Al matrix. Meanwhile, the cast Al microstructure is converted to an equiaxed grain structure with the grain size reduced from ∼ 25 μm to ∼ 2 μm. Finally, the energy consumption of AFSD-enabled upcycling is compared to melt-based recycling; potential pathways are evaluated for energy consumption reduction.

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 degrees 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.

The feasibility of flash sintering boron carbide (B4C) was investigated using a direct current (DC) electric field across different electrodes, field strengths, and thermal profiles. Flash behavior was observed at furnace temperatures as low as 386 degrees C with field strengths of 68-278 V/cm, but only a small channel of the specimen was densified due to hot spot effects. Application of a 2.2 V/cm center dot s voltage ramp at a constant temperature of 550 degrees C caused uniform heating, but at temperatures too low for sintering. Scalable densification of B4C at low furnace temperatures with flash sintering is theorized to be possible by applying a higher current density through power supply or specimen modifications.

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.

The feasibility of processing silicon carbide (SiC) and boron carbide (B4C) using a 2.45 GHz single-mode microwave system has been investigated. In order to determine the appropriate sintering conditions, samples were processed under various electric/magnetic (E/H) field ratios. Proportional 50% E/H-field ratios and 100% H-field conditions resulted in higher sample temperatures up to 1500 °C under equivalent microwave power. Sinterability was improved by adding B4C and carbon to SiC, but limited to a thin outer layer of the pellet. While partial densification was observed under all conditions, isolated regions of full densification in microwave-processed B4C samples were observed under 100% H-field mode. Microstructural analysis of microwave-processed SiC with and without additives indicated non-uniform sintering, while B4C showed evidence of relatively homogeneous microstructures.

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 degrees 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.

Metastable β titanium alloys offer a wide range of attractive property combinations. Conventional processing options have practical limitations in achieving maximum attainable properties and utilizing them to their fullest potential. In the current study, friction stir processing (FSP) of β alloys is explored as a unique path for microstructural engineering. Two metastable β titanium alloys, Ti-1Al-8V-5Fe (Ti-185) and Ti-3Al-8V-6Cr-4Mo-4Zr (Beta C), subjected to FSP with two different tool rotation rates at a constant traverse speed were analyzed in different microstructural conditions. Fully retained β grain structures with grain sizes in the range 4 to 7 µm in Ti-185 and 10 to 15 µm in Beta C were obtained in the as-FSP condition. Post-FSP duplex aging treatment of the low heat input condition resulted in better tensile properties compared to those of high heat input condition, attributable to high number density of nucleation sites generated during FSP. Transmission electron microscopy observations of high-strength Ti-185 sample revealed fine α platelets of length in the range 50 to 130 nm and an aspect ratio in the range 3 to 10, providing significant strengthening contribution. Approximate nose temperatures and nose time calculations of the continuous cooling transformation of β to α were made for various commercial Ti alloys to assess the potential of achieving ultra-high strength levels via FSP.

The use of magnetic fields in ceramic processing has been of interest recently for tailoring the microstructural grain alignment of ceramics in order to improve mechanical, optical, and other properties. However, a number of challenges exist, including the low magnetic response of most ceramic materials (e.g. alumina), and the lack of low viscosity bulk casting systems available for forming ceramics in a magnetic field. In this work, the low magnetic response of alumina was addressed by adding small amounts (~0.04 atom%) of various rare-earth dopants to phase-pure α-alumina to enhance the response of the bulk material, as supported by previous predictive modeling. After identifying the dopant with the highest magnetic response according to a novel, average facial angle alignment metric, a low-viscosity colloidal casting system, based on a single organic additive was selected to allow for the sintering of formed green bodies. This novel process was used to cast bulk ceramic parts under a magnetic field. The effect of magnetic alignment both in the green state and after sintering was investigated. It was found that both erbium and ytterbium improved the magnetic response of alumina, and that the alignment achieved in the green state was maintained through the sintering process, despite removal from the magnetic field.

Various ecological and economical concerns have spurred mankind’s quest for materials that can provide enhanced weight savings and improved fuel efficiency. As part of this pursuit, we have microstructurally tailored an exceptionally high-strength titanium alloy, Ti-6Al-2Sn-4Zr-6Mo (Ti6246) through friction stir processing (FSP). FSP has altered the as-received bimodal microstructure into a unique modulated microstructure comprised of fine acicular α″-laths with nano precipitates within the laths. The sequence of phase transformations responsible for the modulated microstructure and consequently for the strength is discussed with the help of scanning electron microscopy, transmission electron microscopy, and synchrotron X-ray diffraction studies. The specific strength attained in one of the conditions is close to 450 MPa m3/mg, which is about 22% to 85% greater than any commercially available metallic material. Therefore, our novel nano particle strengthened Ti alloy is a potential replacement for many structural alloys, enabling significant weight reduction opportunities.

Alumina (Al2O3) is one of the most widely used ceramic materials for innumerable applications, due to its unique combination of attractive physical and mechanical properties. These intrinsic properties are dictated by the numerous phases that Al2O3 forms and its related phase transformations. Transition metal (TM) cation dopants (iron (Fe), cobalt (Co), nickel (Ni) and manganese (Mn)), even in sparse amounts, have been shown to significantly affect the phase transformation and microstructural evolution of Al2O3. Small concentrations of TM cation dopants have successfully been incorporated to synthesize magnetically active Al2O3, while reducing the θ to α phase transformation temperature by 150 °C, and maintaining the outstanding mechanical properties. In addition, first-principle calculations based on density-functional theory with hybrid functional (HSE06) and the PBE+U methods have provided a mechanistic understanding of the formation energy and magnetism of the TM-doped α and θ phases of Al2O3. The results reveal a potential route for phase transition regulation and external magnetic field-induced texturing of Al2O3 ceramics.

ABSTRACT Energy coupled to matter (ECM) concepts such as magnetic field–assisted processing were used to align rare earth–doped alumina ceramics in the presence of applied fields. The addition of gadolinium and ytterbium dopants to alumina increased the magnetic susceptibility anisotropies, and induced magnetic torques that led to significant alignment of ceramic particles under the application of magnetic fields as low as 1.8 T. In comparison, undoped alumina materials showed minimal alignment under applied field strengths as high as 9 T. Density function theory modeling indicated that the specific dopant type dictated changes in the magnetic properties of different rare earth–doped alumina systems by directly affecting the magnetic moment localization and magnetocrystalline anisotropy.

Solution-based growth of magnetic FePt-FeCo (core-shell) nanoparticles with a controllable shell thickness has been demonstrated. The transition from spin canting to exchange coupling of FePt-FeCo core-shell nanostructures leads to a 28% increase in the coercivity (12.8 KOe) and a two-fold enhancement in the energy product (9.11 MGOe).

Ferroic materials and multiferroics, characterized by their ferroic orders, provide an efficient route for the coupling control of magnetic, mechanical, and electrical subsystems in energy transduction, which aims at converting one form of energy into another. A surge of interest in the ferroic coupling effect has stemmed from its potential use as a new versatile route for energy transduction. Here, the recent progress on the use of (multi)ferroic materials is reviewed, with special emphasis on the fundamental mechanisms that dictate the energy transduction process, including piezoelectricity, pyroelectricity, electrocaloric, magnetostriction, magnetocaloric, elastocaloric, magnetoelectricity, and emerging spin-charge conversion. Research on energy transduction ferroic materials paves the way for ubiquitous energy harvesting through magneto-mechano-electric-thermal coupling mechanisms. Finally, a summary and the future prospective directions of this field are discussed.

A doped non-diamagnetic alumina (Al2O3) would enable the usage of cutting edge technology, such as magnetoforming, to create advanced systems that take advantage of the high chemical and physical resilience of alumina. This study elucidates the magnetic properties of Cr, Fe, Ni, and Cu doped α- and ϑ-alumina. Density functional theory was used to predict the structural, electronic, and magnetic properties of doped alumina, as well as its stability. The results indicate that the dopant species and coordination environment are the most important factors in determining the spin density distribution and net magnetic moment, which will strongly direct the ability of the doped alumina to couple with an external field. Similar coordination environments in different phases produce similar spin densities and magnetic moments, indicating that the results presented in this work may be generalizable to the other five or more phases of alumina not studied here.

The viability of resistively sintering aluminum 5083 powder with an alternating current (AC) was explored under both as-atomized and cryomilled conditions. Samples were processed under an AC field and a direct current (DC) field. Samples processed by both methods exhibited similar microstructures and densities at different die wall temperatures. For as-atomized powders, similar densities (99% of theoretical [TD]) were achieved at die wall temperatures of 564 degrees C under DC fields and 525 degrees C under AC fields. For cryomilled 5083, densities up to 90% of theoretical were achieved at 550 degrees C under DC fields, while density values 99% of TD were achieved at 500 degrees C under AC fields. Based on these findings, it has been determined that AC fields can be used as an alternative to SPS for achieving optimal density.

Shape memory alloys (SMAs) are of high interest as active, adaptive “smart” materials for applications such as sensors and actuators due to their unique properties, including the shape memory effect and pseudoelasticity. Binary NiTi SMAs have shown the most desirable properties, and consequently have generated the most commercial success. A major challenge for SMAs, in particular, is their well-known compositional sensitivity. Therefore, it is critical to control the powder composition and morphology. In this study, a low-pressure, low-temperature hydriding–pulverization–dehydriding method for preparing well-controlled compositions, size, and size distributions of SMA powders from wires is presented. Starting with three different diameters of as-drawn martensitic NiTi SMA wires, pre-alloyed NiTi powders of various well-controlled sizes are produced by hydrogen charging the wires in a heated H3PO4 solution. After hydrogen charging for different charging times, the wires are pulverized and subsequently dehydrided. The wires and the resulting powders are characterized using scanning electron microscopy, differential scanning calorimetry, and X-ray diffraction. The relationship between the wire diameter and powder size is investigated as a function of hydrogen charging time. The rate of diameter reduction after hydrogen charging of wire is also examined. Finally, the recovery behavior due to the shape memory effect is investigated after dehydriding.