Hot Deformation Behavior and Hot Processing Map Construction of the Ti551 Alloy

doi:10.11900/0412.1961.2025.00157

Acta Metall Sin

2026, Vol. 62

Issue (8): 1427-1442 DOI: 10.11900/0412.1961.2025.00157

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Hot Deformation Behavior and Hot Processing Map Construction of the Ti551 Alloy

YIN Jiannian¹, MA Yingjie², YANG Rui², LEI Jiafeng², QI Min²(

), ZHOU Li¹(

)

1 School of Electromechanical and Vehicle Engineering, Yantai University, Yantai 264005, China
2 Shenyang National Laboratory for Materials Science, Institute of Metal Research, Chinese Academy of Sciences, Shenyang 110016, China

Cite this article:

YIN Jiannian, MA Yingjie, YANG Rui, LEI Jiafeng, QI Min, ZHOU Li. Hot Deformation Behavior and Hot Processing Map Construction of the Ti551 Alloy. Acta Metall Sin, 2026, 62(8): 1427-1442.

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Abstract

The Ti551 alloy exhibits exceptional thermal stability, retaining over 80% of its room-temperature strength within 300-400 ^oC, outperforming most α-type Ti alloys. Consequently, it has emerged as the primary structural material for applications in extreme operating environments, such as deep-sea oil drilling pipes. Despite this advantage, the Ti551 alloy exhibits considerably complex thermal deformation behavior and microstructural evolution. Establishing the alloy's precise hot processing window is critical to broaden its engineering applications. Therefore, this study investigated the thermal deformation behavior of the Ti551 alloy using a Gleeble-3500 thermal simulation tester. Specifically, isothermal compression tests were conducted over the temperatures (T) of 800-1100 ^oC and a strain rate ( $ε ˙$ ) of 0.001-10 s^-1. Considering friction and temperature corrections, strain-compensated Arrhenius (SCA) and back-propagation artificial neural network (BPANN) models were selected to establish a constitutive model of the Ti551 alloy. The accuracies of both models were evaluated using the correlation coefficient, average absolute relative error, and relative error. The results demonstrate that the BPANN model outperformed the SCA model, yielding superior accuracy in predicting the flow stress. Thereafter, a hot processing map was constructed based on the dynamic materials model, and the corresponding microstructural evolution during thermal compression was systematically analyzed. Analysis of the hot processing map identified the optimal processing window with the following parameters: $ε ˙$ = 0.001-0.1 s^-1 and T = 900-1050 ^oC. Additionally, the instability zone was primarily concentrated in the high-T, high- $ε ˙$ region (T ≥ 1000 °C, $ε ˙$ ≥ 1 s^-1). These findings demonstrate that the deformation T and $ε ˙$ substantially influenced the flow stress. Specifically, the flow stress markedly increased with the decrease in T or increase in $ε ˙$ . During hot compression, the microstructural evolution of the Ti551 alloy exhibited a close relationship with T and $ε ˙$ , and the dynamic recrystallized grain size notably decreased as T decreased or $ε ˙$ increased. Furthermore, the dominant dynamic recrystallization (DRX) mechanisms during hot deformation comprised continuous and discontinuous DRX processes.

Key words: Ti551 alloy hot deformation behavior constitutive equation hot processing map microstructure

Received: 06 June 2025

ZTFLH:

TG146.23

Fund: National Key Research and Development Program of China(2024YFB3714201);Natural Science Foundation of Shandong Province(ZR2023ME097)

Corresponding Authors: QI Min, Tel: 18742418386, E-mail: mqi17s@imr.ac.cn; ZHOU Li, professor, Tel: 13889124507, E-mail: lizhou@ytu.edu.cn

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	YIN Jiannian
	MA Yingjie
	YANG Rui
	LEI Jiafeng
	QI Min
	ZHOU Li

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https://www.ams.org.cn/EN/10.11900/0412.1961.2025.00157 OR https://www.ams.org.cn/EN/Y2026/V62/I8/1427

Fig.1 Schematic of the hot compression experiment (Inset shows the shape change of the sample before and after the hot compression experiment)

Fig.2 SEM image (a), inverse pole figure (IPF) (b), phase map (c), and kernel average misorientation (KAM) map (d) of the initial microstructure of Ti551 alloy (α_p—primary α, α_s—secondary α)

Fig.3 True stress-strain curves at temperatures (T) of 800 ^oC (a), 900 ^oC (b), 1000 ^oC (c), and 1100 ^oC (d) under different strain rates ( $ε ˙$ ), as well as the true stress-strain curves after friction correction and temperature correction

Fig.4 Temperature changes (ΔT) of Ti551 alloy at $ε ˙$ = 0.001 s^-1 (a),0.01 s^-1 (b),0.1 s^-1 (c), 1 s^-1 (d), and 10 s^-1 (e) under different T

Fig.5 Linear fitting curves of $l n ε ˙$ -lnσ (a), $l n ε ˙$ -σ (b), $l n ε ˙$ -ln[sinh(ασ)] (c), ln[sinh(ασ)]-T^-1 (d), and lnZ-ln[sinh(ασ)] (e) (σ—true stress, α—material constant, Z—Zener-Hollomon parameter)

Table 1 Material constants at different true strains (ε)

Fig.6 Curves of Q (a), lnA (b), n (c), and α (d) with true strain (R²—square of the correlation coefficient R)

Fig.7 Structural diagram of back-propagation artificial neural network (BPANN) model

Fig.8 Effects of the number of neurons in the hidden layer on mean squared error (MSE)

Fig.9 Comparisons of predicted and experimental flow stresses under different $ε ˙$ and T = 800 ^oC (a), 900 ^oC (b), 1000 ^oC (c), and 1100 ^oC (d) (SCA—strain-compensated Arrhenius)

Fig.10 Comparisons of predicted and experimental flow stresses (a, b) and distributions of relative error (c, d) in SCA model (a, c) and BPANN model (b, d) (AARE—average absolute relative error, δ—relative error, δ_min—minimum relative error, δ_max—maximum relative error)

Fig.11 Thermal compression finite element model (a) and load-stroke curves of upper die (b) of Ti551 alloy (v—moving speed of upper die)

Fig.12 Power dissipation maps of Ti551 alloy at true strains of 0.10 (a), 0.30 (b), 0.50 (c), and 0.69 (d) (The isoline values are power dissipation coefficients)

Fig.13 Instability maps of Ti551 alloy at true strains of 0.10 (a), 0.30 (b), 0.50 (c), and 0.69 (d) (The isoline values are instability coefficients)

Fig.14 Processing maps of Ti551 alloy at true strains of 0.10 (a), 0.30 (b), 0.50 (c), and 0.69 (d) (The isoline values are power dissipation coefficients. Region I—instability zone, region Ⅱ—safe processing region, region Ⅲ—optimal processing region)

Fig.15 OM images of Ti551 alloy under different T and $ε ˙$ at strain of 0.69

Fig.16 IPFs of Ti551 alloy under different T and $ε ˙$ at strain of 0.69

Fig.17 KAM maps of Ti551 alloy under different T and $ε ˙$ at strain of 0.69

Fig.18 Strain distribution of Ti551 alloy at T = 1000 ^oC and $ε ˙$ = 1 s^-1 (a) and OM images of regions I (b), II (c), and III (d) in Fig.18a machining region

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