Formation and Thermal Stability of ω-Ti(Fe) in α-Phase-Based Ti(Fe) Alloys

In this work, the formation and thermal stability of the ω-Ti(Fe) phase that were produced by the high-pressure torsion (HPT) were studied in two-phase α-Ti + TiFe alloys containing 2 wt.%, 4 wt.% and 10 wt.% iron. The two-phase microstructure was achieved by annealing the alloys at 470 °C for 4000 h and then quenching them in water. Scanning electron microscopy (SEM) and X-ray diffraction (XRD) were utilized to characterize the samples. The thermal stability of the ω-Ti(Fe) phase was investigated using differential scanning calorimetry (DSC) and in situ high-temperature XRD. In the HPT process, the high-pressure ω-Ti(Fe) phase mainly formed from α-Ti. It started to decompose by a cascade of exothermic reactions already at temperatures of 130 °C. The decomposition was finished above ~320 °C. Upon further heating, the phase transformation proceeded via the formation of a supersaturated α-Ti(Fe) phase. Finally, the equilibrium phase assemblage was established at high temperatures. The eutectoid temperature and the phase transition temperatures measured in deformed and heat-treated samples are compared for the samples with different iron concentrations and for samples with different phase compositions prior to the HPT process. Thermodynamic calculations were carried out to predict stable and metastable phase assemblages after heat-treatments at low (α-Ti + TiFe) and high temperatures (α-Ti + β-(Ti,Fe), β-(Ti,Fe)).

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Thermal stability of a nanocrystalline HfNbTiZr multi-principal element alloy processed by high-pressure torsion

Materials Characterization ◽

10.1016/j.matchar.2020.110550 ◽

2020 ◽

Vol 168 ◽

pp. 110550 ◽

Cited By ~ 2

Author(s):

Pham Tran Hung ◽

Megumi Kawasaki ◽

Jae-Kyung Han ◽

János L. Lábár ◽

Jenő Gubicza

Keyword(s):

Thermal Stability ◽

High Pressure ◽

High Pressure Torsion ◽

Principal Element ◽

Thermal Stability Of

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Thermal Stability of Ultrafine-Grained Pure Titanium Processed by High-Pressure Torsion

Materials Science Forum ◽

10.4028/www.scientific.net/msf.1016.338 ◽

2021 ◽

Vol 1016 ◽

pp. 338-344

Author(s):

Wan Ji Chen ◽

Jie Xu ◽

De Tong Liu ◽

De Bin Shan ◽

Bin Guo ◽

...

Keyword(s):

Activation Energy ◽

Thermal Stability ◽

Grain Size ◽

High Pressure ◽

Annealing Temperature ◽

High Pressure Torsion ◽

Stored Energy ◽

Ultrafine Grained ◽

Average Grain Size ◽

Thermal Stability Of

High-pressure torsion (HPT) was conducted under 6.0 GPa on commercial purity titanium up to 10 turns. An ultrafine-grained (UFG) pure Ti with an average grain size of ~96 nm was obtained. The thermal properties of these samples were studied by using differential scanning calorimeter (DSC) which allowed the quantitative determination of the evolution of stored energy, the recrystallization temperatures, the activation energy involved in the recrystallization of the material and the evolution of the recrystallized fraction with temperature. The results show that the stored energy increases, beyond which the stored energy seems to level off to a saturated value with increase of HPT up to 5 turns. An average activation energy of about 101 kJ/mol for the recrystallization of 5 turns samples was determined. Also, the thermal stability of the grains of the 5 turns samples with subsequent heat treatments were investigated by microstructural analysis and Vickers microhardness measurements. It is shown that the average grain size remains below 246 nm when the annealing temperature is below 500 °C, and the size of the grains increases significantly for samples at the annealing temperature of 600 °C.

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