Near β titanium alloy is widely used in automotive and aerospace industries due to their high strength-to-weight ratio and high corrosion resistance. The near β titanium alloy can precipitate ω phase and α phase after solution and ageing treatment, the strength of which can be remarkably increased, usually at the expense of ductility. It is one of the most important structural components of load-bearing that usually as aircraft skin, shell plating, main frame, linker and special fastener. The alloy used in this paper is a self-developed Ti-Al-V-Mo-Cr-Zr-Fe-Nb ultra-high-strength β titanium alloy, which is a typical near β titanium alloy. The characteristic of isothermal phase transformation of near β titanium alloys is diversity and complexity, which is sensitive to temperature and directly affects the mechanical properties after ageing. In this paper, the microstructural evolution and mechanical properties of a Ti-Al-V-Mo-Cr-Zr-Fe-Nb ultra-high strength β titanium alloy after isothermal treatment were investigated by scanning electron microscopy(SEM), transmission electron microscopy(TEM) and micro-hardness tester. The results show that only the isothermal ω precipitates are formed during ageing at 300℃, and the size of isothermal ω phases increase with the ageing time. The isothermal ω precipitates are first precipitated during ageing at 400℃. With the extension of the ageing time, the α phase nucleation occurs near the ω/β interface. No α precipitates are obtained in the alloy aged at 500℃, and needle-like α precipitates are directly precipitated from the β matrix, which is evenly distributed in the β matrix in a "V" shape. Tensile test shows that the tensile strength of the alloy is 1716.1 MPa and the elongation is 2% after ageing at 400℃ for 12 h. The tensile strength of the alloy is 1439.8 MPa and the elongation is 9.84% after ageing at 500℃ for 12 h, and has a good combination of strength and toughness.
WILLIAMS J C , STARKE E A . Process in structural materials for aerospace[J]. Acta Materialia, 2003, 51 (19): 5775- 5799.
doi: 10.1016/j.actamat.2003.08.023
2
CHEN Y Y , DU Z X , XIAO S L , et al. Effect of aging heat treatment on microstructure and tensile properties of a new β high strength titanium alloy[J]. Journal of Alloys and Compounds, 2014, 586, 588- 592.
doi: 10.1016/j.jallcom.2013.10.096
3
LI T , DAMON K , GANG S , et al. Nucleation driving force for ω-assisted formation of α and associated ω morphology in β-Ti alloys[J]. Scripta Materialia, 2018, 155, 149- 154.
doi: 10.1016/j.scriptamat.2018.06.039
4
HUI Q , XUE X Y , KOU H C , et al. Phase transformation and microstructure evolution in near-β Ti-7333 titanium alloy during aging[J]. Materials Science Forum, 2013, 747/748, 904- 911.
doi: 10.4028/www.scientific.net/MSF.747-748.904
5
JONES N G , DASHWOOD R J , JACKSON M , et al. β phase decomposition in Ti-5Al-5Mo-5V-3Cr[J]. Acta Materialia, 2009, 57 (13): 3830- 3839.
doi: 10.1016/j.actamat.2009.04.031
6
AHMED M , LI T , CASILLAS G , et al. The evolution of microstructure and mechanical properties of Ti-5Al-5Mo-5V-2Cr-1Fe during ageing[J]. Journal of Alloys and Compounds, 2015, 629, 260- 273.
doi: 10.1016/j.jallcom.2015.01.005
7
BANERJEE D , WILLIAMS J C . Perspectives on titanium science and technology[J]. Acta Materialia, 2013, 61 (3): 844- 879.
doi: 10.1016/j.actamat.2012.10.043
HE T , FENG Y , LUO W Z , et al. Research progress of ω phase in near-β titanium alloys[J]. Rare Metal Materials and Engineering, 2018, 47 (2): 705- 710.
9
GAO J H , KNOWLES A J , GUAN D K , et al. ω phase strengthened 1.2 GPa metastable β titanium alloy with high ductility[J]. Scripta Materialia, 2018, 162, 77- 81.
10
NAG S , BANERJEE R , SRINIVASAN R , et al. ω-Assisted nucleation and growth of α precipitates in the Ti-5Al-5Mo-5V-3Cr-0.5Fe β titanium alloy[J]. Acta Materialia, 2009, 57 (7): 2136- 2147.
doi: 10.1016/j.actamat.2009.01.007
11
HE T , FENG Y , LUO W Z , et al. Microstructural evolution of ω assisted α precipitates in β-CEZ alloy during ageing process[J]. Materials Characterization, 2018, 138, 19- 25.
doi: 10.1016/j.matchar.2018.01.056
12
LI T , KENT D , SHA G , et al. The role of ω in the precipitation of α in near-β Ti alloys[J]. Scripta Materialia, 2016, 117, 92- 95.
doi: 10.1016/j.scriptamat.2016.02.026
13
LI T , KENT D , SHA G , et al. The mechanism of ω-assisted α phase formation in near β-Ti alloys[J]. Scripta Materialia, 2015, 104, 75- 78.
doi: 10.1016/j.scriptamat.2015.04.007
HE T , FENG Y , LIU X H , et al. Microstructure evolution of ω and α phase of β-CEZ alloy during the solution treatment and aging process[J]. Rare Metal Materials and Engineering, 2018, 47 (9): 2711- 2716.
15
CHEN W , CAO S , KOU W J , et al. Origin of the ductile-to-brittle transition of metastable β-titanium alloys: self-hardening of ω-precipitates[J]. Acta Materialia, 2019, 170, 187- 204.
doi: 10.1016/j.actamat.2019.03.034
16
LI T , KENT D , SHA G , et al. New insights into the phase transformations to isothermal ω and ω-assisted α in near β-Ti alloys[J]. Acta Materialia, 2016, 106, 353- 366.
doi: 10.1016/j.actamat.2015.12.046
WANG Q J, GAO X, WANG K S, et al. Multi-component alloy composite strengthening high strength titanium alloy and preparation method thereof: CN201310040063.5[P]. 2013-05-22.
WANG Q J , SHUANG Y X , SUN Y L , et al. Process on microstructure and mechanical properties of BTi20 titanium alloy with two forging processes[J]. Rare Metals, 2019, 43 (1): 32- 37.
CHEN Q , WANG Q J , WANG D C , et al. Effect of microstructure inhomogeneity of forgings on microstructure and mechanical properties of new near β titanium alloy[J]. The Chinese Journal of Nonferrous Metals, 2018, 28 (1): 87- 96.
20
尹仁锟. 新型超高强β钛合金相析出特性研究[D]. 西安: 西安建筑科技大学, 2016.
20
YIN R K. Study on phase precipitation characteristics of new type ultra-high strength β titanium alloy [D]. Xi'an: Xi'an University of Architecture and Technology, 2016.
21
李强. 高强β钛合金热处理工艺优化及疲劳性能研究[D]. 西安: 西安建筑科技大学, 2018.
21
LI Q. Study on heat treatment process optimization and fatigue properties of high-strength beta titanium alloy [D]. Xi'an: Xi'an University of Architecture and Technology, 2018.
QIN D Y , LU Y F , LIU Q , et al. Beta to omega transformation in near beta metastable titanium alloys[J]. Materials Review, 2012, 26 (5): 101- 104.
doi: 10.3969/j.issn.1005-023X.2012.05.023
23
PRIMA F , VERMAUT P , TEXIER G , et al. Evidence of α-nanophase heterogeneous nucleation from ω particles in a β-metastable Ti-based alloy by high-resolution electron microscopy[J]. Scripta Materialia, 2006, 54 (4): 645- 648.
doi: 10.1016/j.scriptamat.2005.10.024
24
AZIMZADEH S , RACK H J . Phase transformations in Ti-6.8Mo-4.5Fe-1.5Al[J]. Metallurgical & Materials Transactions A, 1998, 29 (10): 2455- 2467.
doi: 10.1007/s11661-998-0217-8
25
ZHANG X , KOU H C , LI J S , et al. Evolution of the secondary α phase morphologies during isothermal heat treatment in Ti-7333 alloy[J]. Journal of Alloys and Compounds, 2013, 577, 516- 522.
doi: 10.1016/j.jallcom.2013.06.180
26
DONG R F , LI J S , KOU H C , et al. ω-assisted refinement of α phase and its effect on the tensile properties of a near β titanium alloy[J]. Journal of Materials Science & Technology, 2020, 44, 24- 30.
2021, Vol. 49 
), 吴金城, 王伟, 杜忠泽, 尹仁锟
