scholarly journals Formation of Large Size Precipitate-Free Zones in β Annealing of the Near-β Ti-55531 Titanium Alloy

Metals ◽  
2019 ◽  
Vol 9 (5) ◽  
pp. 544 ◽  
Author(s):  
Xueqi Jiang ◽  
Xiaoqiang Shi ◽  
Xiaoguang Fan ◽  
Qi Li
Keyword(s):  
Titanium Alloy ◽  
Phase Transformation ◽  
Heterogeneous Nucleation ◽  
Isothermal Heat Treatment ◽  
Precipitate Free Zone ◽  
Mode Iii ◽  
Slow Cooling ◽  
Free Zone ◽  
Large Size ◽  
Α Phase

Large size (>10000 μm2) precipitate-free zones in the absence of microsegregation were observed in the near-β Ti-55531 titanium alloy after furnace cooling from high temperature and longtime annealing in the single-β phase field. To reveal the formation mechanism of the large size precipitate-free zone, continuous cooling and isothermal heat treatment were carried out to investigate the β-α phase transformation process. It was found that the large size precipitate free zone is attributed to the heterogeneous nucleation of α phase. The nucleation site evolves in three different modes: I-random nucleation inside the β grain, II-network nucleation inside the β grain and, III-heterogeneous nucleation on the precipitated α phase. Modes I and II lead to homogeneous transformed structure while Mode III results in the large size precipitate-free zone. Both modes II and III are promoted at high annealing temperature, rapid cooling above 600 °C or slow cooling below 600 °C. Mode II is common as it can minimize the strain energy in phase transformation. As a result, the formation of the large size precipitate-free zone is not deterministic.

Massive Phase Transformation as a New Prospective on Microstructural Design in a Titanium Alloy - A Review

2020 ◽  
Vol 1000 ◽  
pp. 428-435
Author(s):  
Eung Ryul Baek ◽  
Ghozali Suprobo
Keyword(s):  
Mechanical Property ◽  
Titanium Alloy ◽  
Phase Transformation ◽  
Martensitic Transformation ◽  
Massive Transformation ◽  
Ti Alloy ◽  
Α Phase ◽  
Massive Phase ◽  
Microstructural Design ◽  
And Diffusion

Microstructural design is generally applied to improve the mechanical property of titanium alloy by introducing different phase transformations and thermomechanical treatments. Aside from the martensitic and diffusion transformation, the occurrence of massive transformation occurs in Ti alloy. Massive transformation is categorized as civilian phase transformation, which resulted in the change of crystal structure of an alloy with a given composition without changing the chemical composition of its initial phase. It happened when the body centered-cubic β phase changed into hexagonal closed-pack α phase without decomposing into α+β. Massive transformation involves a diffusion and growth mechanism in a short-range and generally occurs during the introduction of high cooling rates to restrict the full diffusion mechanism. Owing to the nature of a rapid cooling rate as a requirement for massive transformation, the massive phase is normally found together with the product of martensitic transformation. On the other hand, the product of massive transformation is observed as a blocky grain with a featureless characteristic using optical microscopy and. Phase identification using electron backscattered diffraction shows that the region of αm shows only the presence of the α phase. It was reported for containing a high dislocation density similar to martensitic transformation. Specifically, in Ti alloy, the higher magnification using scanning electron microscopy shows fine sub-lamellar morphology, which observed as a combination product morphology between martensitic and diffusion transformation. It resulted in the mechanical property of the massive phase is between those two morphologies. Hence, it brings a new perspective on designing the microstructure of Ti alloy, which can be used to improve the mechanical property of Ti alloy.

In-situ observation of deformation induced α″ phase transformation in a β-titanium alloy

2016 ◽  
Vol 182 ◽  
pp. 281-284 ◽  
Author(s):  
Tingting Yao ◽  
Kui Du ◽  
Yulin Hao ◽  
Shujun Li ◽  
Rui Yang ◽  
...  
Keyword(s):  
Titanium Alloy ◽  
Phase Transformation ◽  
In Situ Observation ◽  
Α Phase

Influence of Cooling Rate on Phase Transformation of a α+β Titanium Alloy

2016 ◽  
Vol 849 ◽  
pp. 327-331
Author(s):  
Yue Fei ◽  
Xin Nan Wang ◽  
Guo Qiang Shang ◽  
Jing Li ◽  
Li Wei Zhu ◽  
...  
Keyword(s):  
Titanium Alloy ◽  
Phase Transformation ◽  
Cooling Rate ◽  
Micro Hardness ◽  
X Ray Diffraction ◽  
Cooling Rates ◽  
X Ray ◽  
Lamellar Structures ◽  
Optical Micrograph ◽  
Α Phase

Effect rules of cooling rate on phase transformation and microstructure of a α+β titanium alloy were studied by thermal dilatometer method. Specimens under different cooling rates from 0.05°C/s to 2.5°C/s were analyzed by using X-ray diffraction (XRD), optical micrograph (OM) and Vickers micro-hardness. The results showed that the starting temperature of β to α phase transformation gradually decreased with the increase of cooling rate. The finishing temperature of β to α phase transformation firstly decreased and then increased with the increase of cooling rate. The typical lamellar structures were observed under the cooling rates from 0.05°C/s to 0.2°C/s. The layer thickness of α phase became thinner and the precipitation content of α phase reduced under the cooling rate of 0.5°C/s. The α phase was fine acicular and the precipitation content of α phase reduced obviously under the cooling rate of 2.5°C. The effect rule of cooling rate on micro-hardness was that the value of micro-hardness firstly decreased and then increased with the cooling rate increasing.

Double Annealing Processes of Ti-5Al-5Mo-5V-1Cr-1Fe Titanium Alloy

2019 ◽  
Vol 944 ◽  
pp. 33-37
Author(s):  
Qing Rui Wang ◽  
Ai Xue Sha ◽  
Li Jun Huang ◽  
Xing Wu Li ◽  
Guang Bao Mi
Keyword(s):  
Mechanical Property ◽  
Titanium Alloy ◽  
Phase Transformation ◽  
Grain Boundary ◽  
Annealing Temperature ◽  
Small Deformation ◽  
Annealing Process ◽  
Air Cooling ◽  
Large Size ◽  
Comprehensive Property

In this work, double annealing processes of Ti-5Al-5Mo-5V-1Cr-1Fe titanium alloy were systemically investigated, and the microstructure and property of different processes were compared. The results show that, when the first stage annealing is air cooling, the microstructure with continuous and straight grain boundary is obtained, and corresponding mechanical property is not very good; When the first stage annealing is furnace cooling, the influence of first stage annealing temperature on microstructure and property is obvious. Excellent comprehensive property can be obtained when β grain boundary and a phase are discontinuous and tortuous. Further, based on this research, a new double annealing process is developed, which can obtain excellent ductility when large size forging is fabricated above the phase transformation point and has small deformation.

Phase Transformation and Microstructure Evolution in Near-β Ti-7333 Titanium Alloy during Aging

2013 ◽  
Vol 747-748 ◽  
pp. 904-911 ◽  
Author(s):  
Qiong Hui ◽  
Xiang Yi Xue ◽  
Hong Chao Kou ◽  
Min Jie Lai ◽  
Bin Tang ◽  
...  
Keyword(s):  
Titanium Alloy ◽  
Phase Transformation ◽  
Grain Boundaries ◽  
Parent Phase ◽  
Solution Treatment ◽  
Ageing Treatment ◽  
Β Phase ◽  
Α Phase ◽  
Nucleation Sites ◽  
Higher Temperature

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.

Influence of High Magnetic Field on β-a Phase Transformation in TC4 Titanium Alloy

2014 ◽  
Vol 941-944 ◽  
pp. 112-115
Author(s):  
Hong Ming Wang ◽  
Guirong Li ◽  
Yue Ming Li ◽  
Yu Hua Cui ◽  
Cong Xiang Peng ◽  
...  
Keyword(s):  
Magnetic Field ◽  
Titanium Alloy ◽  
Phase Transformation ◽  
High Magnetic Field ◽  
Volume Fraction ◽  
Positive Influence ◽  
Pulsed Magnetic Field ◽  
Tc4 Titanium Alloy ◽  
Α Phase

In the TC4 titanium alloy subject to high pulsed magnetic field, the phase transformation from α to β occurs. When the magnetic induced intensity increased from 2T, 3T to 4T with constant 30 pulses, the percent of α phase adds up gradually. When the magnetic induced intensity is 4T the volume fraction of α phase amounts up to 59%. It is ascertained that magnetic field has taken a positive influence on the phase transformation because of the variation of inner energy induced by magnetic field.

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