Transmission electron microscopy identification of a new Ti–Al–Fe intermetallic compound
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A new intermetallic phase has been discovered in the Ti–Al–Fe system. It was first found in a commercial ferrotitanium alloy and then confirmed in a specially prepared experimental alloy. Its crystal structure and chemical composition were investigated using various transmission electron microscopy (TEM) techniques, namely selected area and convergent beam electron diffraction, high-resolution lattice imaging, energy-dispersive X-ray spectroscopy and electron energy-loss spectroscopy (EELS). TEM investigations were complemented by other characterization techniques—scanning electron microscopy, electron-probe microanalysis with wavelength spectrometers, X-ray diffraction and scanning Auger microscopy, as well as quantitative metallography and microhardness measurements. The compound contains 68–74 at.% Ti, 20–24 at.% Fe and 3.5–7 at.% Al. Its crystal lattice is body-centred orthorhombic with periods a ≈ b and c/a ≈ 1.04. The lattice parameters are about four times larger than those of β-Ti (bcc with a = 0.325 nm) and of the TiFe intermetallic (CsCl-type structure with a = 0.298 nm). Apparently, the crystal unit cell of the compound is composed of 4 × 4 × 4 body-centred subcells and contains 128 atoms; the Pearson symbol of the crystal structure is oI128. The new phase was designated β2, thus hinting at its possible relation to β-Ti.
KeywordsElectron Diffraction Pattern Microstructural Component Wavelength Spectrometer Foil Edge Convergent Beam Diffraction Pattern
This research was undertaken as a core project in the Advanced Materials Program at CANMET Materials Technology Laboratory (Dr. Jason Lo, Program Manager). The ferrotitanium alloy was provided by the Ivaco Rolling Mills, L’Original, ON, Canada. A number of people at CANMET provided experimental support: Ms. Catherine Bibby prepared TEM specimens, Dr. Jian Li helped with EPMA measurements, Dr. John Wilson performed X-ray diffractometry, Mr. John Neima carried out Auger spectroscopy, Ms. Pei Liu assisted with metallography and microhardness measurements, and Mr. Jacob Kruszewski and Ms. Ruby Zhang helped with preparation of the experimental alloy and heat treatment.
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