Ultra-fine grained microstructure of metastable beta Ti-15Mo alloy and its effects on the phase transformations

Václavová, Kristína; Stráský, Josef; Zháňal, Pavel; Veselý, Jozef; Polyakova, Veronika; Semenova, Irina P.; Janeček, Miloš

doi:10.1088/1757-899x/194/1/012021

Cited by 13 publications

(18 citation statements)

References 20 publications

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“…HPT straining results in the formation of a UFG structure of the Ti15Mo alloy [15,17,[29][30][31][32]. In the rudimentary stage of the HPT deformation, a twinning process takes place, which is followed by significant grain refinement [31,33,34].…”

Section: Discussionmentioning

confidence: 99%

Phase Transformations upon Ageing in Ti15Mo Alloy Subjected to Two Different Deformation Methods

Bartha

Stráský

Veverková

et al. 2021

Metals

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Ti15Mo alloy was subjected to two techniques of intensive plastic deformation, namely high pressure torsion and rotary swaging at room temperature. The imposed strain resulted in the formation of an ultrafine-grained structure in both deformed conditions. Detailed inspection of the microstructure revealed the presence of grains with a size of around 100 nm in both conditions. The microstructure after rotary swaging also contained elongated grains with a length up to 1 µm. Isothermal ageing at 400 °C and 500 °C up to 16 h was applied to both conditions to investigate the kinetics of precipitation of the α phase and the recovery of lattice defects. Positron annihilation spectroscopy indicated that the recovery of lattice defects in the β matrix had already occurred at 400 °C and, in terms of positron trapping, was partly compensated by the precipitation of incoherent α particles. At 500 °C the recovery was fully offset by the formation of incoherent α/β interfaces. Contrary to common coarse-grained material, in which the α phase precipitates in the form of lamellae, precipitation of small and equiaxed α particles occurred in the deformed condition. A refined two-phase equiaxed microstructure with α particles and β grain sizes below 1 μm is achievable by simple rotary swaging followed by ageing.

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Section: Discussionmentioning

confidence: 99%

Phase Transformations upon Ageing in Ti15Mo Alloy Subjected to Two Different Deformation Methods

Bartha

Stráský

Veverková

et al. 2021

Metals

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“…The equivalent inserted von Mises strain after a single HPT rotation (N = 1, r = 10 mm and thickness h of 1 mm) ranges from 0 (the exact center) up to 35 = 3500% (periphery). Such extreme strain results in a dislocation density exceeding ρ = 5 × 10 14 m −2 and grain size in the range of hundreds of nanometers [11,26]. The objective of this study was to investigate the effect of SPD on the mechanisms and kinetics of α phase precipitation and to compare it with the precipitation in the non-deformed solution-treated material.…”

Section: Introductionmentioning

confidence: 99%

Effect of the High-Pressure Torsion (HPT) and Subsequent Isothermal Annealing on the Phase Transformation in Biomedical Ti15Mo Alloy

Bartha

Stráský

Veverková

et al. 2019

Metals

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Ti15Mo metastable beta Ti alloy was solution treated and subsequently deformed by high-pressure torsion (HPT). HPT-deformed and benchmark non-deformed solution-treated materials were annealed at 400 °C and 500 °C in order to investigate the effect of UFG microstructure on the α-phase precipitation. Phase evolution was examined using laboratory X-ray diffraction (XRD) and by high-energy synchrotron X-ray diffraction (HEXRD), which provided more accurate measurements. Microstructure was observed by scanning electron microscopy (SEM) and microhardness was measured for all conditions. HPT deformation was found to significantly enhance the α phase precipitation due the introduction of lattice defects such as dislocations or grain boundaries, which act as preferential nucleation sites. Moreover, in HPT-deformed material, α precipitates are small and equiaxed, contrary to the α lamellae in the non-deformed material. ω phase formation is suppressed due to massive α precipitation and consequent element partitioning. Despite that, HPT-deformed material after ageing exhibits the high microhardness exceeding 450 HV.

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“…Milled powder is significantly deformed and contains high amount of lattice defects. Recent results show that α-phase precipitation is significantly enhanced in severely deformed materials [19].…”

Section: Discussionmentioning

confidence: 99%

Ti-15Mo alloy prepared by cryogenic milling and spark plasma sintering

et al. 2020

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In this study, Ti-15Mo alloy powder was prepared by gas atomization and subsequent cryogenic milling in order to achieve ultra-fine grained microstructure. Both milled and non-milled powders were compacted by spark plasma sintering (SPS) at temperature of 800 °C for different sintering times up to 6 minutes. Sintering temperature and time affect porosity, microstructure and phase composition of the alloy. Milled powder can be sintered at comparatively lower temperature to achieve fully dense material. Sintering below β-transus temperature results in α+β-structure. Furthermore, amount of α-phase is higher in the material sintered from the milled powder due to increased oxygen content and also due to refined microstructure which facilitates α-phase precipitation. Mechanical properties are also affected by formation of ω-phase during uncontrolled cooling in the SPS machine.

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Ultra-fine grained microstructure of metastable beta Ti-15Mo alloy and its effects on the phase transformations

Cited by 13 publications

References 20 publications

Phase Transformations upon Ageing in Ti15Mo Alloy Subjected to Two Different Deformation Methods

Phase Transformations upon Ageing in Ti15Mo Alloy Subjected to Two Different Deformation Methods

Effect of the High-Pressure Torsion (HPT) and Subsequent Isothermal Annealing on the Phase Transformation in Biomedical Ti15Mo Alloy

Ti-15Mo alloy prepared by cryogenic milling and spark plasma sintering

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