Scanning Electron Microscope With An Energy Dispersive Spectrometer Research Articles

Preparation of mica-based glass-ceramics with needle-like fluorapatite

Objectives The aim of this study was to prepare mica-based glass-ceramics containing needle-like fluorapatites, and to understand the relationship between the composition, the microstructure and mechanical properties. Methods The specimens were prepared by casting and subsequent heat treatment. The crystalline phases in the specimens were determined by X-ray diffraction (XRD). The microstructures of the fractured surface were examined by using a scanning electron microscope with an energy dispersive spectrometer (SEM/EDS). The Vickers hardness and fracture toughness were determined by the indentation method. Statistical analysis of the results was performed by one-way analysis of variance (ANOVA) and Tukey's test. The bioactivity of the glass-ceramics was evaluated by soaking the polished specimens in the simulated body fluid (SBF). Results Needle-like fluorapatite crystals were successfully obtained in mica-based glass-ceramics by controlling the heat treatment process. The formation of needle-like fluorapatite crystals, instead of particle-like crystals reported in previous studies, can be attributed to the one-dimensional rapid growth of fluorapatite along the c-axis. The mechanical properties of the glass-ceramics are related to the fluorapatite content. The higher the fluorapatite content, the higher the Vickers hardness and the fracture toughness ( p < 0.01). The bioactivity test showed that the needle-like fluorapatite-containing glass-ceramics possess very good bioactivity. Significance As the needle-like fluorapatite crystal has the same morphology as human bones, it endows the mica-based glass-ceramics with good bioactivity. Moreover, the needle-like fluorapatite crystal toughens the base glass-ceramics. Therefore, the mica-based glass-ceramics with needle-like fluorapatite have the potential for the restoration of bone defects and implants.

Evaluation of microstructure and phase relations in a powder processed Ti-44AI-12Nb alloy

Titanium aluminides based on the ordered face-centered tetragonal γTiAI phase possess attractive properties, such as low density, high melting point, good elevated temperature strength, modulus retention, and oxidation resistance, making these alloys potential high-temperature structural materials. These alloys can be processed by both ingot metallurgy and powder metallurgy routes. In the present study, three variations of the powder metallurgy route were studied to process a Ti-44Al-12Nb (at. %) alloy: (a) cold pressing followed by reaction sintering (CPprocess); (b) cold pressing, vacuum hot pressing, and then sintering (HP process); and (c) arc melting, hydride-dehydride process to make the alloy powder, cold isostatic pressing, and then sintering (AM process). Microstructural and phase relations were studied by x-ray diffraction (XRD) analysis, optical microscopy, scanning electron microscopy with an energy-dispersive spectrometer (SEM-EDS), and electron probe microanalysis (EPMA). The phases identified were Ti3AI and TiAl; an additional Nb2AI phase was observed in the HPsample. The microstructures of CPand HP processed samples are porous and chemically inhomogeneous whereas the AM processed sample revealed fine equiaxed microstructure. This refinement of the microstructure is attributed to the fine, homogeneous powder produced by the hydride-dehydride process and the high compaction pressures.