α phase growth and branching in titanium alloys

ω-phase particles formed in β-titanium alloys (bcc structure) act important roles to their mechanical properties such as ductility and hardness. About the ductility, fine ω-phase particles in β–titanium alloys improve the ductility, because ω-phase crystals becomes nucleation sites of α-phase and it is well known that (β+α) duplex alloys have higher ductility. In the present study, the formation sites and the formation mechanism of ω-phase crystals due to external stress and aging are investigated using the conventional and high resolution electron microscopy.A β-titanium alloy (Til5Mo5Zr) was supplied by Kobe Steel Co., and a single crystal was prepared by a zone refining method. Plates with {110} surface were cut from the crystal and were pressured hydrostatically, and stressed by rolling and tensile testing. Specimens for aging with tensile stress were also prepared from Ti20Mo polycrystals. TEM specimens from these specimens were prepared by a twin-jet electron-polishing machine. A JEM 4000EX electron microscope operated at 400k V was used for taking dark field and HREM images.

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Influence of crystallographic α-phase texture on mechanical property anisotropy of sheets made of pseudo-α and (α+β) titanium alloys

Deformation and Fracture of Materials ◽

10.31044/1814-4632-2020-7-20-25 ◽

2020 ◽

Vol 7 ◽

pp. 20-25

Author(s):

M. G. Isaenkova ◽

◽

O. A. Krymskaya ◽

Ya. A. Babich ◽

P. N. Medvedev ◽

...

Keyword(s):

Mechanical Property ◽

Titanium Alloys ◽

Α Phase ◽

Property Anisotropy ◽

Mechanical Property Anisotropy

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Design of Low-Cost and High-Strength Titanium Alloys Using Pseudo-Spinodal Mechanism through Diffusion Couple Technology and CALPHAD

Materials ◽

10.3390/ma14112910 ◽

2021 ◽

Vol 14 (11) ◽

pp. 2910

Author(s):

Chaoyi Ding ◽

Chun Liu ◽

Ligang Zhang ◽

Di Wu ◽

Libin Liu

Keyword(s):

Diffusion Couple ◽

Titanium Alloys ◽

High Throughput ◽

Volume Fraction ◽

Raw Materials ◽

Low Cost ◽

High Strength ◽

High Yield ◽

Α Phase ◽

Cr System

The high cost of development and raw materials have been obstacles to the widespread use of titanium alloys. In the present study, the high-throughput experimental method of diffusion couple combined with CALPHAD calculation was used to design and prepare the low-cost and high-strength Ti-Al-Cr system titanium alloy. The results showed that ultra-fine α phase was obtained in Ti-6Al-10.9Cr alloy designed through the pseudo-spinodal mechanism, and it has a high yield strength of 1437 ± 7 MPa. Furthermore, application of the 3D strength model of Ti-6Al-xCr alloy showed that the strength of the alloy depended on the volume fraction and thickness of the α phase. The large number of α/β interfaces produced by ultra-fine α phase greatly improved the strength of the alloy but limited its ductility. Thus, we have demonstrated that the pseudo-spinodal mechanism combined with high-throughput diffusion couple technology and CALPHAD was an efficient method to design low-cost and high-strength titanium alloys.

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Oxygen Induced Phase Transformation in TC21 Alloy with a Lamellar Microstructure

Metals ◽

10.3390/met11010163 ◽

2021 ◽

Vol 11 (1) ◽

pp. 163

Author(s):

Shu Wang ◽

Yilong Liang ◽

Hao Sun ◽

Xin Feng ◽

Chaowen Huang

Keyword(s):

Electron Microscopy ◽

Phase Transformation ◽

Oxygen Uptake ◽

Titanium Alloys ◽

Electron Backscatter Diffraction ◽

Lamellar Microstructure ◽

Α Phase ◽

Transmission Electron ◽

The Matrix ◽

Oxygen Ingress

The main objective of the present study was to understand the oxygen ingress in titanium alloys at high temperatures. Investigations reveal that the oxygen diffusion layer (ODL) caused by oxygen ingress significantly affects the mechanical properties of titanium alloys. In the present study, the high-temperature oxygen ingress behavior of TC21 alloy with a lamellar microstructure was investigated. Microstructural characterizations were analyzed through optical microscopy (OM), scanning electron microscopy (SEM), electron backscatter diffraction (EBSD), and transmission electron microscopy (TEM). Obtained results demonstrate that oxygen-induced phase transformation not only enhances the precipitation of secondary α-phase (αs) and forms more primary α phase (αp), but also promotes the recrystallization of the ODL. It was found that as the temperature of oxygen uptake increases, the thickness of the ODL initially increases and then decreases. The maximum depth of the ODL was obtained for the oxygen uptake temperature of 960 °C. In addition, a gradient microstructure (αp + β + βtrans)/(αp + βtrans)/(αp + β) was observed in the experiment. Meanwhile, it was also found that the hardness and dislocation density in the ODL is higher than that that of the matrix.

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Eliminating continuous grain boundary α phase in laser melting deposited near β titanium alloys by heat treatment

IOP Conference Series Materials Science and Engineering ◽

10.1088/1757-899x/563/2/022025 ◽

2019 ◽

Vol 563 ◽

pp. 022025

Author(s):

Penglin Li ◽

Changmeng Liu ◽

Jie Wang ◽

Jiping Lu ◽

Shuyuan Ma ◽

...

Keyword(s):

Heat Treatment ◽

Grain Boundary ◽

Titanium Alloys ◽

Laser Melting ◽

Α Phase

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The Role of Martensitic Transformation in Thermomechanical Development of Microstructure and Plasticity of Two-Phase Ti-6Al-4V Titanium Alloy

Key Engineering Materials ◽

10.4028/www.scientific.net/kem.687.3 ◽

2016 ◽

Vol 687 ◽

pp. 3-10 ◽

Cited By ~ 1

Author(s):

Maciej Motyka ◽

Jan Sieniawski ◽

Waldemar Ziaja

Keyword(s):

Plastic Deformation ◽

Titanium Alloy ◽

Martensitic Transformation ◽

Titanium Alloys ◽

Thermomechanical Processing ◽

Solution Treatment ◽

Phase Morphology ◽

Two Phase ◽

Α Phase ◽

Hot Plasticity

Phase constituent morphology in microstructure of two-phase α+β titanium alloys is determined by conditions of thermomechanical processing consisting of sequential heat treatment and plastic deformation operations. Results of previous research indicate that particularly solution treatment preceding plastic deformation significantly changes α-phase morphology and determines hot plasticity of titanium alloys. In the paper thermomechanical processing composed of β solution treatment and following hot forging of Ti-6Al-4V titanium alloy was analysed. Development of martensite plates during heating up and hot deformation was evaluated. Microscopic examinations revealed that elongated and deformed α-phase grains were fragmented and transformed into globular ones. Significant influence of martensitic transformation on elongation coefficient of α-phase grains after plastic deformation was confirmed. Based on results of elevated temperature tensile tests it was established that α-phase morphology in examined two-phase α+β titanium alloy, developed in the thermomechanical processing, can enhance their hot plasticity – especially in the range of low strain rates.

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