Crystallographic and morphological relationships between β phase and the Widmanstätten and allotriomorphic α phase at special β grain boundaries in an α/β titanium alloy

A newly near-β titanium alloy Ti-7Mo-3Cr-3Nb-3Al (Ti-7333) was subjected to β phase solution treatment and ageing in the present work. The characteristics of α phase transformation in ageing treatment were studied. Results show that isothermal aging at a low temperature (350) will result in lots of ω particles with small size homogeneously distributing in the parent phase. These ω particles can act as nucleation sites for α phase and lead to the uniform precipitation of fine α phase within the β grain after further ageing treatment. However, when ageing at a higher temperature, the α phase tends to precipitate direct from the β matrix and the morphology of α phase is determined by the temperature and period of ageing treatment. After aging at 550 for 5min, acicular α phase precipitates in the β grains as well as along β grain boundaries and the size and quantity of α phase increase with the holding time. Note that Ti-7333 alloy has a quick ageing response. When aging at 700 for 1h, coarser α laths precipitate both on the grain boundary and within the grain. Increase the ageing temperature to 800, α phase precipitates within the β grain as short rod-like morphology. It is suggested that the driving force for α phase nucleation and the amount of defects in the intragranular decrease with the increasing of temperature, leading to the grain boundaries become the prior nucleation sites. Substantial α phase precipitate-free regions adjacent to β grain boundaries remained after ageing at 700 for 1h due to the rejection of β-stabilizer from coarse α lath on β grain boundaries. Aging at 800 for 1h resulted in pronounced continuous α-films along β grain boundaries.

Download Full-text

Microstructural Analysis and Wear Behavior of Cryogenically Treated Ti-6Al-4V Alloy

Applied Mechanics and Materials ◽

10.4028/www.scientific.net/amm.592-594.1331 ◽

2014 ◽

Vol 592-594 ◽

pp. 1331-1335 ◽

Cited By ~ 1

Author(s):

Haider Nasreen ◽

S. Beer Mohamed ◽

S. Rasool Mohideen

Keyword(s):

Grain Boundaries ◽

Wear Behavior ◽

Cryogenic Treatment ◽

Microstructural Analysis ◽

Wear Loss ◽

Β Phase ◽

Α Phase ◽

Treated Sample

This paper helps in understanding the effects of cryogenic treatment on microstructural variation, hardness and wear behavior of Ti-6Al-4V alloy. The microstructure indicates white β-phase dispersed on the grain boundaries of dark α-phase. Cryogenic treatment at-186 °C for 10 h led to the transformation from β-phase to α-phase, resulting in coarsening of α. Hardness of the cryogenically treated sample was observed to decrease and wear loss was observed to increase; this can be attributed to the coarsening of α-phase.

Download Full-text

Influences of Solution Temperatures on Microstructure and Mechanical Properties of near α Titanium Alloy

Materials Science Forum ◽

10.4028/www.scientific.net/msf.1035.89 ◽

2021 ◽

Vol 1035 ◽

pp. 89-95

Author(s):

Chao Tan ◽

Zi Yong Chen ◽

Zhi Lei Xiang ◽

Xiao Zhao Ma ◽

Zi An Yang

Keyword(s):

Mechanical Properties ◽

Titanium Alloy ◽

High Temperature ◽

Room Temperature ◽

Solution Temperature ◽

Vacuum Induction Melting ◽

Induction Melting ◽

Β Phase ◽

Α Phase ◽

New Type

A new type of Ti-Al-Sn-Zr-Mo-Si series high temperature titanium alloy was prepared by a water-cooled copper crucible vacuum induction melting method, and its phase transition point was determined by differential thermal analysis to be Tβ = 1017 °C. The influences of solution temperature on the microstructures and mechanical properties of the as-forged high temperature titanium alloy were studied. XRD results illustrated that the phase composition of the alloy after different heat treatments was mainly α phase and β phase. The microstructures showed that with the increase of the solution temperature, the content of the primary α phase gradually reduced, the β transformation structure increased by degrees, then, the number and size of secondary α phase increased obviously. The tensile results at room temperature (RT) illustrated that as the solution temperature increased, the strength of the alloy gradually increased, and the plasticity decreased slightly. The results of tensile test at 650 °C illustrated that the strength of the alloy enhanced with the increase of solution temperature, the plasticity decreased first and then increased, when the solution temperature increased to 1000 °C, the alloy had the best comprehensive mechanical properties, the tensile strength reached 714.01 MPa and the elongation was 8.48 %. Based on the room temperature and high temperature properties of the alloy, the best heat treatment process is finally determined as: 1000 °C/1 h/AC+650 °C/6 h/AC.

Download Full-text

Microstructure Evolution of near α Titanium Alloy during Multi-Step Thermomechanical Deformation Process

Materials Science Forum ◽

10.4028/www.scientific.net/msf.1035.305 ◽

2021 ◽

Vol 1035 ◽

pp. 305-311

Author(s):

Qing Shan Liu ◽

Bo Long Li ◽

Tong Bo Wang ◽

Cong Cong Wang ◽

Peng Qi ◽

...

Keyword(s):

Titanium Alloy ◽

High Temperature ◽

Hot Deformation ◽

Deformation Temperature ◽

Strain Curve ◽

Optical Microscope ◽

Phase Content ◽

Β Phase ◽

Α Phase ◽

Gleeble 3500

A new type of near α high temperature titanium alloy of Ti-Al-Sn-Zr-Mo-Si-Er was studied. The samples with different primary α phase content were prepared by solid solution at 950 °C/1 h—1010 °C/1 h. The multi-step hot compression experiments were carried out by Gleeble-3500 in a sequence of upper region of α + β phase, then followed by lower region of α + β phase. The effects of primary α phase content and deformation temperature on the microstructure of the alloy were studied by means of true stress-strain curve and optical microscope. The results show that the content of primary α phase gradually decreases from 45.4% at 950°C to 0% at 1010°C. As the deformation temperature decreases from 940°C to 900°C, the content of α phase increases gradually from 65% to 94%, which is changed from dynamic recrystallization to deformed structure elongated along RD direction. It is found that the arrangement of α phase along RD direction is the longest at 920°C. With the increase of the deformation temperature in the multi-step high temperature region from 970°C to 990°C, the width of deformed α phase decreases from 3.64 μm at 970°C to 2.71 μm at 990°C. The optimized microstructure is composed of 20% primary α phase arranged along RD direction. This process has a certain potential in the process of hot deformation of the alloy. Key words: high temperature titanium alloy, primary α phase, multi-step hot deformation

Download Full-text

High-Temperature Deformation Behavior and Microstructural Characterization of Ti-35421 Titanium Alloy

Materials ◽

10.3390/ma13163623 ◽

2020 ◽

Vol 13 (16) ◽

pp. 3623 ◽

Cited By ~ 2

Author(s):

Danying Zhou ◽

Hua Gao ◽

Yanhua Guo ◽

Ying Wang ◽

Yuecheng Dong ◽

...

Keyword(s):

Titanium Alloy ◽

Dynamic Recrystallization ◽

Strain Rate ◽

Hot Deformation ◽

Deformation Behavior ◽

Deformation Temperature ◽

Phase Region ◽

Temperature Deformation ◽

Β Phase ◽

Α Phase

A self-designed Ti-35421 (Ti-3Al-5Mo-4Cr-2Zr-1Fe wt%) titanium alloy is a new type of low-cost high strength titanium alloy. In order to understand the hot deformation behavior of Ti-35421 alloy, isothermal compression tests were carried out under a deformation temperature range of 750–930 °C with a strain rate range of 0.01–10 s−1 in this study. Electron backscatter diffraction (EBSD) was used to characterize the microstructure prior to and post hot deformation. The results show that the stress–strain curves have obvious yielding behavior at a high strain rate (>0.1 s−1). As the deformation temperature increases and the strain rate decreases, the α phase content gradually decreases in the α + β phase region. Meanwhile, spheroidization and precipitation of α phase are prone to occur in the α + β phase region. From the EBSD analysis, the volume fraction of recrystallized grains was very low, so dynamic recovery (DRV) is the dominant deformation mechanism of Ti-35421 alloy. In addition to DRV, Ti-35421 alloy is more likely to occur in continuous dynamic recrystallization (CDRX) than discontinuous dynamic recrystallization (DDRX).

Download Full-text

Evolution of grain boundary α phase during cooling from β phase field in a α+β titanium alloy

Materials Letters ◽

10.1016/j.matlet.2021.130318 ◽

2021 ◽

pp. 130318

Author(s):

Xiongxiong Gao ◽

Saifei Zhang ◽

Kun Yang ◽

Peng Wang

Keyword(s):

Titanium Alloy ◽

Grain Boundary ◽

Phase Field ◽

Β Phase ◽

Α Phase

Download Full-text

Material Characterisation and Computational Thermal Modelling of Electron Beam Powder Bed Fusion Additive Manufacturing of Ti2448 Titanium Alloy

Materials ◽

10.3390/ma14237359 ◽

2021 ◽

Vol 14 (23) ◽

pp. 7359

Author(s):

Qiushuang Wang ◽

Wenyou Zhang ◽

Shujun Li ◽

Mingming Tong ◽

Wentao Hou ◽

...

Keyword(s):

Titanium Alloy ◽

Electron Beam ◽

Thermal History ◽

Computational Modelling ◽

Layer By Layer ◽

Powder Bed Fusion ◽

Material Microstructure ◽

Powder Bed ◽

Β Phase ◽

Α Phase

Ti-24Nb-4Zr-8Sn (Ti2448) is a metastable b-type titanium alloy developed for biomedical applications. In this work, cylindrical samples of Ti2448 alloy have been successfully manufactured by using the electron beam powder bed fusion (PBF-EB) technique. The thermal history and microstructure of manufactured samples are characterised using computational and experimental methods. To analyse the influence of thermal history on the microstructure of materials, the thermal process of PBF-EB has been computationally predicted using the layer-by-layer modelling method. The microstructure of the Ti2448 alloy mainly includes β phase and a small amount of α” phase. By comparing the experimental results of material microstructure with the computational modelling results of material thermal history, it can be seen that aging time and aging temperature lead to the variation of α” phase content in manufactured samples. The computational modelling proves to be an effective tool that can help experimentalists to understand the influence of macroscopic processes on material microstructural evolution and hence potentially optimise the process parameters of PBF-EB to eliminate or otherwise modify such microstructural gradients.

Download Full-text

Continuous Dynamic Recrystallization in Dual-Phase Titanium Alloy in Superplasticity

Defect and Diffusion Forum ◽

10.4028/www.scientific.net/ddf.385.126 ◽

2018 ◽

Vol 385 ◽

pp. 126-130 ◽

Cited By ~ 1

Author(s):

Keita Sekiguchi ◽

Hiroshi Masuda ◽

Hirobumi Tobe ◽

Eiichi Sato

Keyword(s):

Titanium Alloy ◽

Dynamic Recrystallization ◽

Early Stage ◽

Continuous Dynamic Recrystallization ◽

New Class ◽

Β Phase ◽

Α Phase ◽

Slip Planes ◽

The Difference ◽

Continuous Dynamic

A new class of superplastic titanium alloy, Ti–4.5Al–2.5Cr–1.2Fe–0.1C–0.3Cu–0.3Ni, was deformed at 1073 K with strain rates of 1×10−4–1×10−1 s−1, and microstructures in the condition between superplastic regions II and III (= 1×10−2 s−1) were observed using scanning electron microscope and electron back-scattered diffraction. Continuous dynamic recrystallization was observed, resulting in grain refinement both in α and β phases. The grain size decreased significantly in α phase at the early stage of the deformation and in β phase at the later stage. In the recrystallized microstructure, the major sub-boundaries formed perpendicularly to slip directions <11−20> in α phase and parallel to slip planes {110} in β phase, which might be caused by the difference in the symmetry of the crystal structures.

Download Full-text

Effect of Third-Stage Heat Treatments on Microstructure and Properties of Dual-Phase Titanium Alloy

Materials ◽

10.3390/ma14112776 ◽

2021 ◽

Vol 14 (11) ◽

pp. 2776

Author(s):

Xiqin Mao ◽

Meigui Ou ◽

Desong Chen ◽

Ming Yang ◽

Wei Long

Keyword(s):

Tensile Strength ◽

Titanium Alloy ◽

Aging Treatment ◽

Air Cooling ◽

Phase Zone ◽

Two Phase ◽

Β Phase ◽

Solution Treated ◽

Α Phase ◽

Third Stage

Two-phase TC21 titanium alloy samples were solution-treated at 990 °C (β phase zone) and cooled by furnace cooling (FC), air cooling (AC), and water quenching (WQ), respectively. The second solution stage treatment was carried out at 900 °C (α + β phase zone), then aging treatment was performed at 590 °C. The influence of the size and quantity of the α phase on the properties of the sample were studied. The experimental results showed as the cooling rate increased after the first solution stage treatment, wherein the thickness of primary layer α gradually decreased, and the tensile strength and yield strength gradually increased. After the second solution stage treatment, the tensile properties of samples increased due to the quantity of layers α increased. The aging treatment promoted the precipitation of the dispersed α phase and further improved the tensile strength. After the third solution stage treatments, the FC samples with more β-phase had the best comprehensive mechanical properties.

Download Full-text

The Heat Treatment Influence on the Microstructure and Hardness of TC4 Titanium Alloy Manufactured via Selective Laser Melting

Materials ◽

10.3390/ma11081318 ◽

2018 ◽

Vol 11 (8) ◽

pp. 1318 ◽

Cited By ~ 19

Author(s):

Zhan-Yong Zhao ◽

Liang Li ◽

Pei-Kang Bai ◽

Yang Jin ◽

Li-Yun Wu ◽

...

Keyword(s):

Heat Treatment ◽

Titanium Alloy ◽

Critical Temperature ◽

Selective Laser Melting ◽

Heat Treatment Temperature ◽

Treatment Temperature ◽

Laser Melting ◽

Β Phase ◽

Α Phase ◽

Increasing Temperature

In this research, the effect of several heat treatments on the microstructure and microhardness of TC4 (Ti6Al4V) titanium alloy processed by selective laser melting (SLM) is studied. The results showed that the original acicular martensite α′-phase in the TC4 alloy formed by SLM is converted into a lamellar mixture of α + β for heat treatment temperatures below the critical temperature (T0 at approximately 893 °C). With the increase of heat treatment temperature, the size of the lamellar mixture structure inside of the TC4 part gradually grows. When the heat treatment temperature is above T0, because the cooling rate is relatively steep, the β-phase recrystallization transforms into a compact secondary α-phase, and a basketweave structure can be found because the primary α-phase develop and connect or cross each other with different orientations. The residence time for TC4 SLM parts when the treatment temperature is below the critical temperature has little influence: both the α-phase and the β-phase will tend to coarsen but hinder each other, thereby limiting grain growth. The microhardness gradually decreases with increasing temperature when the TC4 SLM part is treated below the critical temperature. Conversely, the microhardness increases significantly with increasing temperature when the TC4 SLM part is treated above the critical temperature.

Download Full-text