Growth Behavior of Grain Boundary α Phase and Its Effect on the Microtexture During β → α Phase Transformation in Ti6246 Titanium Alloys

doi:10.11900/0412.1961.2023.00002

Acta Metall Sin

2025, Vol. 61

Issue (2): 265-277 DOI: 10.11900/0412.1961.2023.00002

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Growth Behavior of Grain Boundary α Phase and Its Effect on the Microtexture During β → α Phase Transformation in Ti6246 Titanium Alloys

QI Min¹^,², WANG Qian², MA Yingjie¹^,²(

), CAO Hemeng¹^,², HUANG Sensen², LEI Jiafeng¹^,², YANG Riu¹^,²

1 School of Materials Science and Engineering, University of Science and Technology of China, Shenyang 110016, China
2 Shichangxu Innovation Center for Advanced Materials, Institute of Metal Research, Chinese Academy of Sciences, Shenyang 110016, China

Cite this article:

QI Min, WANG Qian, MA Yingjie, CAO Hemeng, HUANG Sensen, LEI Jiafeng, YANG Riu. Growth Behavior of Grain Boundary α Phase and Its Effect on the Microtexture During β → α Phase Transformation in Ti6246 Titanium Alloys. Acta Metall Sin, 2025, 61(2): 265-277.

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Abstract

The initial lamellar microstructure of titanium alloys significantly affects their microstructural evolution and mechanical property during thermo-mechanical treatments. Thus, the evolution of the initial lamellar microstructure must be explored to control the microstructure and enhance the mechanical property. The present work focuses on the evolution of the lamellar microstructure during β→α phase transformation via interrupted furnace cooling experiments to analyze the growth behavior of the grain boundary α phase (α_GB) and its effect on the subsequent growth of intragranular α lamellae and microtexture. Results show that when titanium alloy furnace cools from the β phase field to the α + β phase field, the α_GB holding Burgers orientation relationship (BOR) with both sides of β grains (2-BOR α_GB) has an advantage for early transformation at the β grain boundary. In particular, type II (49.5°/<110>) and type III (60°/<110>) β grain boundaries are preferential sites for the early nucleation of α_GB particles. As the temperature decreases, α lamellae holding similar orientation to 2-BOR α_GB grow to both sides of β grains. Thus, 2-BOR α_GB and both sides of α lamellae form a strong microtexture at the grain boundary. At the early growth period of the α phase, the smaller the θ_2-BOR (misorientation of the close-oriented α_GB variant pair of parents β1 and β2) of 2-BOR α_GB, the earlier the formation of a strong microtexture at the grain boundary. 2-BOR α_GB preferentially precipitates, whereas the α_GB holding BOR with only one side of the β grain (1-BOR α_GB) nucleates. α lamellae holding a similar orientation to 1-BOR α_GB grow to one side of the BOR-β grain (holding BOR with α_GB), whereas α lamellae with a different orientation grow in the non-BOR-β grain. Thus, 1-BOR α_GB and one side of α lamellae form a weak microtexture at the grain boundary.

Key words: α + β titanium alloy phase transformation preferred growth grain boundary α phase microtexture

Received: 03 January 2023

ZTFLH:

TG146.2

Fund: National Key Research and Development Program of China(2021YFC2801801);National Natural Science Foundation of China(51871225)

Corresponding Authors: MA Yingjie, professor, Tel: 13840026329, E-mail: yjma@imr.ac.cn

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	QI Min
	WANG Qian
	MA Yingjie
	CAO Hemeng
	HUANG Sensen
	LEI Jiafeng
	YANG Riu

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https://www.ams.org.cn/EN/10.11900/0412.1961.2023.00002 OR https://www.ams.org.cn/EN/Y2025/V61/I2/265

Fig.1 Schematics of the heat treatment processes (T—temperature, t—time, F.C.—furnace cooling, W.Q.—water quenching, T_β —β-transus temperature)
(a) β annealing treatment (b) interrupted furnace cooling treatment

Fig.2 Low (a) and high (b) magnified SEM images of the as-received Ti6246 alloy (α_p—primary α, α_s—secondary α)

Fig.3 OM image of the lamellae microstructure of Ti6246 alloy after β annealing treatment

Fig.4 EBSD analyses of Ti6246 alloy after β annealing treatment, showing typical Widmanstätten microstructures
(a, b) band contrast map (a) and the corresponding α orientation map (b) (α_GB—grain boundary α phase) (c, d) SEM image (c) and the corresponding α orientation map (d)

Fig.5 OM images of α phase in the Ti6246 alloy after furnace cooling from β phase field to 920 ^oC (a), 880 ^oC (b), 840 ^oC (c), and 810 ^oC (d)

Fig.6 SEM images of α phase in the Ti6246 alloy after furnace cooling from β phase field to 920 ^oC (a), 880 ^oC (b), 840 ^oC (c), and 810 ^oC (d)

Fig.7 Volume fractions of the α_GB and α colony as a function of temperature below T_β in Ti6246 alloy

Fig.8 EBSD analyses of the α phase in the Ti6246 alloy after furnace cooling from β phase field to 920 ^oC (a), 880 ^oC (b), and 840 ^oC (c) (The area enclosed by dashed line in Fig.8c indicates that the β phase has not yet transformed to α phase)

Table 1 Fractions of the β phase grain boundary transformed to α_GB in Ti6246 alloy after furnace cooling from β phase field to different temperatures

Fig.9 EBSD analyses of the α phase grain at multiple positions (a-d) of Ti6246 alloy after furnace cooling from β phase field to 880 ^oC, pole overlaps as shown in black boxes

Fig.10 EBSD analyses of α_GB in the Ti6246 alloy after furnace cooling from β phase field to 880 ^oC
(a) SEM image (b, d) orientation map (b) and pole figure (d) of α phase corresponding to the square area in Fig.10a (c, e) orientation map (c) and pole figure (e) of β phase corresponding to the square area in Fig.10a

Fig.11 EBSD analyses of 2-BOR α_GB in the Ti6246 alloy after furnace cooling from β phase field to 880 ^oC, pole overlaps as shown in black boxes
(a, c) orientation map (a) and corresponding pole figure (c) of α phase (b, d) orientation map (b) and corresponding pole figure (d) of β phase

Fig.12 Probabilities of two colonies emitted by α_GB grains as a function of θ_2-BOR in Ti6246 alloy after furnace cooling from β phase field to 880 ^oC (Numbers of observed boundaries are indicated in the figure)

Fig.13 Schematics of the transformation of the microtexture when the Ti alloy was cooled from a β phase field
(a) 2-BOR α_GB and both sides of α lamellae forming strong microtexture
(b) 1-BOR α_GB and one side of α lamellae forming weak microtexture

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