Effect of O Content on the Aging Precipitation Behavior and Mechanical Properties of Ti2448 Alloy

doi:10.11900/0412.1961.2024.00107

Acta Metall Sin

2025, Vol. 61

Issue (12): 1790-1802 DOI: 10.11900/0412.1961.2024.00107

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Effect of O Content on the Aging Precipitation Behavior and Mechanical Properties of Ti2448 Alloy

LI Dan¹^,², GONG Delun¹, HAO Yulin¹(

)

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

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LI Dan, GONG Delun, HAO Yulin. Effect of O Content on the Aging Precipitation Behavior and Mechanical Properties of Ti2448 Alloy. Acta Metall Sin, 2025, 61(12): 1790-1802.

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Abstract

Metastable β-titanium alloys are widely used in advanced biomedical applications because of their high strength and low modulus. Strength improvements in these alloys are mainly achieved through α-phase precipitation. Interestingly, a novel α″ + β dual-phase microstructure has been discovered in a multifunctional Ti2448 alloy after aging treatments, which effectively enhanced the strength while maintaining decent ductility. Since O plays a crucial role in regulating the decomposition and mechanical properties of titanium alloys, understanding its effects on the microstructural evolution and mechanical behavior of Ti2448 alloys is of great importance. However, the effect of O on the decomposition behavior of the Ti2448 alloy remains unclear. To investigate the influence of O content on the microstructure evolution and mechanical properties of the Ti2448 alloy, two Ti2448 alloys with different oxygen contents were selected: low oxygen (LO: 0.08%, mass fraction) and high oxygen (HO: 0.33%, mass fraction). This study employed a two-step heat treatment (annealing at 873/923 K for 10 min, followed by aging at 773 K for 1-4 h) on Ti2448-LO and Ti2448-HO alloys, focusing on the evolution of their microstructure and mechanical properties. Results indicated that O content minimally influenced the phase composition and grain size of the alloys before heat treatment. However, increasing the O content considerably suppressed the double yield phenomenon and enhanced the strength and elastic modulus of the alloy. After the two-step heat treatment, both alloys exhibited the precipitation of dense lamellar phases, resulting in remarkable modulus hardening and aging strengthening. Although the initial thickness of the precipitated phase was relatively unaffected by the O content, its subsequent coarsening behavior during aging was influenced. Under the same heat treatment conditions, the Ti2448-HO alloy exhibited a higher volume fraction of precipitates, leading to stronger modulus hardening and aging strengthening. Consequently, the aged Ti2448-HO alloy exhibited higher elastic modulus and strength than the Ti2448-LO alloy.

Key words: metastable β titanium alloy O content heat treatment precipitate mechanical property

Received: 15 April 2024

ZTFLH:

TG156.1

Fund: National Natural Science Foundation of China(U2341259)

Corresponding Authors: HAO Yulin, professor, Tel: (024)83978841, E-mail: ylhao@imr.ac.cn

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	LI Dan
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https://www.ams.org.cn/EN/10.11900/0412.1961.2024.00107 OR https://www.ams.org.cn/EN/Y2025/V61/I12/1790

Table 1 Chemical compositions of Ti2448 alloys

Fig.1 Schematic of two-step heat treatment process for Ti2448 alloys with different O contents (RT—room temperature)

Fig.2 Electron channeling contrast imaging (ECCI) images of as-rolled Ti2448-LO (a) and Ti2448-HO (b) alloys

Fig.3 Bright field TEM images of as-rolled Ti2448-LO (a) and Ti2448-HO (b) alloys (Insets in Figs.3a and b show the corresponding SAED patterns of β phase)

Fig.4 XRD spectra of as-rolled Ti2448-LO and Ti2448-HO alloys

Fig.5 Engineering stress-strain curves of the as-rolled Ti2448-LO (a) and Ti2448-HO (b) alloys

Table 2 Elastic moduli (E) and hardnesses of as-rolled Ti2448-LO and Ti2448-HO alloys

Fig.6 ECCI images of Ti2448-LO (a) and Ti2448-HO (b) alloys after annealing at 873 K for 10 min

Fig.7 ECCI images of Ti2448-LO (a) and Ti2448-HO (b) alloys after annealing at 923 K for 10 min

Fig.8 XRD spectra of Ti2448-LO and Ti2448-HO alloys after annealing at 873 and 923 K for 10 min

Fig.9 Bright field (a) and dark field (b) TEM images of precipitates in Ti2448-LO alloys after annealing at 873 K for 10 min and followed by aging at 773 K for 1 h (Inset in Fig.9b shows the SEAD pattern taken along [ $0 1 ¯ 1$ ] _β zone axis, φ—characterisitic angle)

Fig.10 Bright field (a) and dark field (b) TEM images of precipitates in Ti2448-HO alloys after annealing at 873 K for 10 min and followed by aging at 773 K for 1 h (Inset in Fig.10b shows the corresponding SAED pattern taken along [ $0 1 ¯ 1$ ] _β zone axis)

Fig.11 ECCI images (a-f) and ECCI images processed by MIPAR software (a1-f1) of Ti2448-LO (a-c, a1-c1) and Ti2448-HO (d-f, d1-f1) alloys after annealing at 873 K for 10 min and followed by aging at 773 K for different time
(a, a1, d, d1) 1 h (b, b1, e, e1) 2 h (c, c1, f, f1) 4 h

Fig.12 ECCI images of Ti2448-LO (a-c) and Ti2448-HO (d-f) alloys after annealing at 923 K for 10 min and followed by aging at 773 K for 1 h (a, d), 2 h (b, e), and 4 h (c, f)

Table 3 Thicknesses (τ), number densities (ρ), and volume fractions (V) of the precipitates in Ti2448-LO and Ti2448-HO alloys under 873 K, 10 min + 773 K, 1-4 h conditions

Fig.13 Evolutions of elastic moduli of Ti2448-LO和Ti2448-HO alloys with different heat treatment processes
(a) 873 K, 10 min + 773 K, 1-4 h (b) 923 K, 10 min + 773 K, 1-4 h

Fig.14 Evolutions of hardnesses of Ti2448-LO和Ti2448-HO alloys with different heat treatment processes
(a) 873 K, 10 min + 773 K, 1-4 h (b) 923 K, 10 min + 773 K, 1-4 h

Fig.15 Engineering stress-strain curves of Ti2448-LO (a) and Ti2448-HO (b) alloys treated by different heat treatment processes

Table 4 τ, ρ, and V of the precipitates in Ti2448-LO and Ti2448-HO alloys under 923 K, 10 min + 773 K, 1-4 h conditions

Table 5 Room temperature mechanical properties of Ti2448-LO and Ti448-HO alloys treated by different heat treatment processes

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