Key Engineering Materials Vol. 616

Abstract: High performance Al-doped Li₇La₃Zr₂O₁₂ (LLZO) solid electrolytes were successfully prepared by plasma activated sintering method. The effect of Al₂O₃ concentration on the microstructure and ionic conductivity of Li₇La₃Zr₂O₁₂ was investigated. Without addition of Al₂O₃, only tetragonal phase was obtained at temperature range of 1000-1200 °C. Pure cubic phase of LLZO was obtained with the addition of 1.2-1.8 wt.% Al₂O₃. The pellet sintered at 1150 °C with 1.5 wt.% content of Al₂O₃ had a maximum relative density of 99.8 % with total ionic conductivity of 5.7×10⁻⁴ S/cm at room temperature. Al₂O₃ can stabilize the cubic LLZO phase which promotes the transformation of LLZO from tetragonal to cubic phase.

Abstract: α-LiAl₅O₈, γ-LiAlO₂, α-Al₂O₃ and those composite films were prepared on AlN polycrystalline substrates by laser chemical vapor deposition (LCVD), and the effects of total pressure (P_tot) and the molar ratio of Li to Al (R_Li/Al) on the morphology and deposition rates were investigated. The typical morphology of single-phase γ-LiAlO₂ films prepared at R_Li/Al > 1.0 and P_tot > 400 Pa was granular, whereas γ-LiAlO₂ films prepared at P_tot < 200 Pa and γ-LiAlO₂-α-LiAl₅O₈ composite films had pyramidal grains. Single-phase α-LiAl₅O₈ films showed polygonally faceted morphologies. Composite films of α-LiAl₅O₈ and α-Al₂O₃ consisted of carifllower-like and faceted grains. A single-phase γ-LiAlO₂ film deposited at 200 Pa showed the maximum deposition rate of 48 μm h^-1.

Abstract: Thick (over 1 mm) β-SiC films were deposited at a deposition temperature of 1823 K and a total pressure of 4 kPa by halide CVD using SiCl₄ and CH₄ as precursors, and H₂ as carrier gas. The maximum deposition rate was 1125 μm h⁻¹. The SiC films showed strong (220) preferred orientation. The grain size increased from 20 to 100 μm with increasing C/Si ratio.

Abstract: The surface of silicon carbide (SiC) powder was modified by coating with amorphous silica (SiO₂) using (C₂H₅O₄)Si (tetraethyl orthosilicate: TEOS) as a precursor by rotary chemical vapor deposition (RCVD). With increasing deposition time from 0.9 to 14.4 ks, the mass content of SiO₂ coating increased from 1 to 35 mass%. The SiO₂ mass content had a linear relationship with deposition time from 2.7 to 7.2 ks. The effects of O₂ gas flow, deposition temperature (T_dep), total pressure (P_tot) and precursor vaporization temperature (T_vap) on the SiO₂ yield by RCVD were investigated. At O₂ gas flow of 4.2 × 10^-7 m³ s^-1, T_dep of 948 K, P_tot of 400 Pa and deposition time of 7.2 ks, the maximum SiO₂ yield of 1.82 × 10^-7 kg/s with SiC powder of 4.5 × 10^-3 kg by RCVD was obtained.

Abstract: Nanoporous structured alumina templates for the synthesis of Fe nanowires were synthesized by the anodization of aluminium metal under various synthetic conditions in some acid solutions. Subsequently, using this nanoporous structured alumina as a template, Fe nanowires with some tens nanometer in diameter and some micron in length was successfully synthesized by both electrodeposition process into various types of porous alumina templates and chemical treatments in mixed-acid solutions to remove the templates. Effects of anodization treatments of aluminium for a porous template on the microstructure of Fe nanowires and nanorods were examined. As a result, the morphology of Fe products obtained by electrodeposition process could be designed with the template obtained under the synthetic conditions (anodization temperatures and electrodeposition conditions etc).

Abstract: Microcellular polymeric foam is a new class of materials which has been widely used in many industries. The foaming of polymethyl metacrylate (PMMA) using supercritical carbon dioxide (ScCO₂) which is inexpensive and environmental friendly has been studied to better understand the foaming process. The pieces of PMMA are put into a saturation vessel of which temperature and pressure are kept constant. Supercritical carbon dioxide (ScCO₂) at temperature between 65 °C and 105 °C and pressure between 8 MPa and 16 MPa is used as a foaming agent. After saturation of carbon dioxide, rapid decompression of ScCO₂ saturated PMMA yields expanded microcellular foams. The densities of foamed PMMA materials are tested by true density analyzer, while the microstructures of a variety of density foamed PMMA materials are characterized by scaning electron microscopy (SEM). The cell size and cell density are calculated via image analysis. The effect of the process condition on the cell morphologies and mass density of the foam is investigated by considering the solubility of carbon dioxide in PMMA. The relationship between the mass density of foamed PMMA (ρ) and foaming temperature (T) and pressure (P) are respectively certained quantificationally.

Abstract: We investigate the perpendicular magnetic anisotropy dependence on the AlO capping layer in Pt/Co/AlO films. AlO was deposited on Pt/Co films by RF magnetron sputtering and atomic layer deposition (ALD) with varying thickness. It is found that the prolonged deposition of thick AlO layers by RF magnetron sputtering causes significant damage to the Pt/Co underneath while AlO layers formed by ALD can be of arbitrary thickness with no damage to the magnetic properties of the films. The decline of the magnetic properties can be attributed to the method of AlO deposition for each process. In the RF magnetron sputtering, AlO atoms with high kinetic energy are ejected from a sputter target resulting in the degradation of Pt/Co films, while the process of deposition of AlO by ALD is governed by a series of chemically reactive condensations allowing for arbitrary deposition thickness of AlO.

Abstract: Dense mesoporous alumina bulks were successfully synthesized by a hydrothermal hot-pressing (HHP) method for mesoporous alumina powders prepared as starting material with a high BET surface area and narrow pore size distribution. As a result, mesoporous alumina HHP bulks had high density with uniformity pore size distribution and a high specific surface area. Their microstructural features for dense mesoporous alumina bulks were observed by SEM. The characterization of mesopores was examined.

Abstract: The precipitation behavior during heat treatment and resulting mechanical properties of ASTM F 90 Co-20Cr-15W-10Ni (mass%) alloys were investigated with regards to their biomedical applications. Heat treatment was conducted at temperatures of 873 to 1623 K, for a holding time of 259.2 ks. The precipitates produced were then electrolytically extracted from the alloys and analyzed by X-ray diffraction (XRD). This revealed that the precipitates formed were an M₂₃X₆ type and/or η-phase (i.e., an M₆X-M₁₂X type). The M₂₃X₆-type precipitate was detected across the entire heat-treatment temperature range; however, the η-phase precipitate was only detected at 1073 to 1473 K, becoming dominant at 1173 to 1373 K. The formation of M₂₃X₆ type precipitates at 873 K is shown to improve the mechanical properties of this alloy, whereas the domination by the η-phase precipitate at higher temperatures causes deterioration in the ductility.

Abstract: The effect of high-pressure torsion (HPT) processing on the microstructure and Vickers hardness of Co-Cr-Mo (CCM) alloys were investigated in this study. The microstructure of initial CCM alloy contains equiaxed grains with a grain diameter of approximately 50 μm and twins. The clear grain boundaries of equiaxed grains and twins disappear after HPT processing at a rotation number, N, of 10. The phase maps of initial CCM alloy and CCM alloy subjected to HPT processing at N = 5 measured by electron backscatter diffraction exhibit that the ratio of γ phase decreases from 93.5% to 34.1% and the ratio of ε phase increases from 6.5% to 65.9% by applying HPT processing. These results indicate that the ε phase is formed by high-strain, which is induced by the HPT processing. The Vickers hardness values on the surfaces of the CCM alloys subjected to HPT processing at N = 1, 5, and 10 increase with increasing the equivalent strain, ε_eq. These results suggest that an increase of Vickers hardness is correlated to an increase of the ratio of ε phase and the dislocation density, and grain refinement, which are caused by the high-strain induced by HPT processing.