The Phase Transformations Induced by High-Pressure Torsion in Ti–Nb-Based Alloys

The study of the fundamentals of the α → ω and β → ω phase transformations induced by high-pressure torsion (HPT) in Ti–Nb-based alloys is presented in the current work. Prior to HPT, three alloys with 5, 10, and 20 wt% of Nb were annealed in the temperature range of 700–540°C in order to obtain the (α + β)-phase state with a different amount of the β-phase. The samples were annealed for a long time in order to reach equilibrium Nb content in the α-solid solution. Scanning electron microscope (SEM), transmission electron microscopy, and X-ray diffraction techniques were used for the characterization of the microstructure evolution and phase transformations. HPT results in a strong grain refinement of the microstructure, a partial transformation of the α-phase into the ω-phase, and a complete β → ω phase transformation. Two kinds of the ω-phase with different chemical compositions were observed after HPT. The first one was formed from the β-phase, enriched in Nb, and the second one from the almost Nb-pure α-phase. It was found that the α → ω phase transformation depends on the Nb content in the initial α-Ti phase. The less the amount of Nb in the α-phase, the more the amount of the α-phase is transformed into the ω-phase

Structural and Mechanical Properties of Ti-Co Alloys Treated by High Pressure Torsion

The microstructure and properties of titanium-based alloys can be tailored using severe plastic deformation. The structure and microhardness of Ti–4 wt.% Co alloy have been studied after preliminary annealing and following high pressure torsion (HPT). The Ti–4 wt.% Co alloy has been annealed at 400, 500, and 600 °C, i.e., below the temperature of eutectoid transformation in the Ti–4 wt.% Co system. The amount of Co dissolved in α-Ti increased with increasing annealing temperature. HPT led to the transformation of α-Ti in ω-Ti. After HPT, the amount of ω-phase in the sample annealed at 400 °C was about 80­85%, i.e., higher than in pure titanium (about 40%). However, with increasing temperature of pre-annealing, the portion of ω-phase decreased (60–65% at 500 °C and about 5% at 600 °C). The microhardness of all investigated samples increased with increasing temperature of pre-annealing

Raman microspectroscopy as a unique method of the investigation of acid proof steel foil oxidation

In this paper, the results of the investigation of the morphology and phase composition of the oxide layers formed on the surface of the 1H18N9T acid proof steel foil by confocal Raman micro-spectroscopy with optical microscopy, SEM, XRD and TEM-EDS-SADP are presented. The foil oxidation was performed by thermo-programmed heating up to 823, 1023 or 1113 K and next annealing at the final temperatures in the air flow for 48 h, 4 h and 4 h, respectively. The great advantages of the use of the Raman spectroscopy for the phase determining in the oxide layers on the acid proof steel foil are shown. Moreover the possibility of applying the optical microscopy for investigation of the surface morphology of both the initial steel foil and the oxide layers is pointed out

Effect of Mo on stability of quasicrystalline phase in Al-Mn-Fe alloy

Microstructure evolution in rapidly solidified Al91Mn 6Fe2Mo1 ribbons after annealing was investigated using X-ray diffraction, scanning electron microscopy and analytical transmission electron microscopy including in situ heating experiment in TEM. As spun ribbons consisted of icosahedral quasicrystalline particles enriched in Fe, Mn and Mo embedded in an aluminium matrix. A small amount of quasicrystals containing Fe and Mn which coexisted with the Al3(Fe, Mn) phase was also observed between the aluminium grains. Further annealing experiments and subsequent analysis of microstructure changes in the sample showed that the quasicrystalline particles underwent a transformation into stable crystalline phases at temperatures which depended on their composition. It was observed that quasicrystals enriched in Mn and Fe transformed at much lower temperatures than primary quasicrystals with Mo content. It was noticed that two different crystalline phases formed in dependence on the temperature of annealing. The Al6(Mn, Fe) phase appeared first at the quasicrystal/matrix interface. At higher temperature, the Al12(Mn, Mo) phase formed due to reaction of the Al6(Mn, Fe) phase with the aluminium matrix. Microstructural and DSC investigations showed that addition of molybdenum improved thermal stability of the quasicrystals in Al-Mn-Fe system. © 2012 Elsevier B.V. All rights reserved

SEM and TEM Characterization of NiAl2O4 Spinel Phase in Al2O3 Matrix Ni Composite

score: 0collation: 222-22

Carbon nanotubes, silica and titania supported heteropolyacid H3PW12O40H_{3}PW_{12}O_{40} as the catalyst for ethanol conversion

The new catalyst: heteropolyacid H 3 PW 12 O 40 (HPA) supported on carbon nanotubes (CNTs) for ethanol conversion was compared with silica and titania supported heteropolyacid. The ethanol conversion did not depend on the type of the support up to reaction temperature 403 K while above 423 K ethanol conversion was higher for HPA on CNTs than for unsupported HPA. Generally, the most active catalysts were obtained by using high surface area silica as the support