Single Annealing on Microstructure and Mechanical Properties of a Short-Term High-Temperature Titanium Alloy AITranslate
Abstract AITranslate
With the development of the aerospace industry，the flight speed of high-performance aircraft has continuously increased，raising interest in high-temperature titanium alloys for short-term use above 600 ℃. Ti-6.5Al-2Sn-4Zr-1.5Mo-2Nb-0.5Fe-0.2Si alloy is a new titanium alloy designed for such short-term high-temperature service conditions. A small amount of Fe was added to improve processing performance and reduce raw material cost. This study systematically investigated the effect of single annealing temperature on the microstructure，room temperature，and 650 ℃ tensile properties of this alloy. The experimental material was produced by triple vacuum arc remelting and rolled in α+β phase region. The original microstructure was bimodal，and the β-transus temperature （Tβ） was determined as 1010~1020 ℃. The alloy was annealed at temperatures below Tβ （950，970，990 ℃），near Tβ （1010 ℃），and above Tβ （1040 ℃） for 2 h followed by air cooling （AC）. Microstructure was characterized using optical microscopy （OM），scanning electron microscopy （SEM），electron backscatter diffraction （EBSD），and electron probe microanalysis （EPMA）. Mechanical properties were evaluated by tensile tests at room temperature and 650 ℃. Microstructure analysis showed that annealing temperature significantly influenced phase composition and microstructure. Below Tβ，Ti-6.5Al-2Sn-4Zr-1.5Mo-2Nb-0.5Fe-0.2Si alloy exhibited a bimodal structure consisting of equiaxed primary α phase （αp） and β transformed structure （βt）. As the annealing temperature increased from 950 to 990 ℃，αp size remained nearly unchanged，while its volume fraction gradually decreased. In contrast，the content and diameter of βt increased，with the change becoming more pronounced as the temperature approached Tβ. Near Tβ （1010 ℃），αp content dropped sharply to about 3%，βt size grew rapidly to 88 μm，and the secondary α lamellar （αs） thickness reached 1000 nm. Some αp particles were located inside β grains. Above Tβ （1030 ℃），αp disappeared and a fully lamellar structure formed，characterized by coarse prior β grains and basket-weave α lamellar with specific orientation relationships between lamellar of different types. EPMA results indicated that the contents of β-stabilizing elements Mo，Nb，and Fe in αp phase were significantly lower than in βt structure. Compared with Nb，Mo and Fe exhibited more pronounced segregation，with very low contents in αp phase. As the annealing temperature increased，Al content in βt structure gradually rose，while the contents of Mo，Nb，and Fe generally showed a decreasing trend. Consequently，the stability of β phase decreased，leading to a tendency to form thicker αs laths during the AC process. Tensile tests results revealed a close relationship between room temperature properties and microstructural evolution. After annealing in the range of 950~990 ℃，αp volume fraction reached or exceeded 30%，leading to excellent deformation compatibility. The elongation exceeded 20% and the reduction of area reached 53%. Meanwhile，the increase in βt size and αs lamellar thickness weakened the grain refinement strengthening effect，resulting in a slight decrease in room temperature strength with rising annealing temperature. When the annealing temperature increased to 1010 ℃ or above，the sharp reduction or disappearance of αp concentrated deformation in the lamellar structure. Dislocation slip was hindered，causing a significant deterioration in room temperature plasticity，with marked decreases in elongation and reduction of area. Analysis of 650 ℃ tensile properties showed that with increasing annealing temperature，both yield strength and tensile strength continuously rose，while elongation gradually decreased. After annealing at 950~990 ℃，the increased αs lath thickness reduced the number of interfaces that were easy to migrate at high temperature，leading to a slight increase in strength and a decrease in ductility. After annealing at 1010 ℃ or above，the disappearance of αp and the significant coarsening of β grains reduced the number of grain boundaries，further enhancing high-temperature strength. However，the poor deformation compatibility of the lamellar structure caused a sharp drop in high-temperature ductility. Comparison showed that Ti-6.5Al-2Sn-4Zr-1.5Mo-2Nb-0.5Fe-0.2Si alloy annealed at 1010 ℃ for 2 h AC achieved a better balance of comprehensive properties：its 650 ℃ tensile strength reached 555 MPa while room temperature elongation remained at 13%，indicating a good combination of high-temperature strength and room temperature ductility. Fracture analysis further illustrated the influence of annealing temperature and microstructure on fracture behavior. At room temperature，the fracture morphology changed from deep dimples （ductile） to cleavage steps （quasi-cleavage/cleavage） with varying microstructure. The fracture mode shifted from ductile fracture （990 ℃） to quasi-cleavage fracture （1010 ℃） and then to cleavage fracture （1040 ℃）. At 650 ℃，all specimens exhibited ductile fracture. However，in the fully lamellar structure （1040 ℃），a rock-candy-like fracture feature was observed due to crack propagation along β grain boundaries. In summary，by adjusting the single annealing temperature，the content of αp，the size of β grains，and the morphology of α lamellar in Ti-6.5Al-2Sn-4Zr-1.5Mo-2Nb-0.5Fe-0.2Si alloy could be effectively controlled，thereby optimizing the balance between room temperature and high-temperature properties. This study demonstrated that annealing near Tβ （e.g.，1010 ℃） could reconcile room temperature ductility with short-term high-temperature strength in this kind of alloy.
KeyWords AITranslate
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Basic Information:
DOI：10.13373/j.cnki.cjrm.XY20030037
Chinese Library Classification Number:TG146.2+3
Citation Information:
With the development of the aerospace industry，the flight speed of high-performance aircraft has continuously increased，raising interest in high-temperature titanium alloys for short-term use above 600 ℃. Ti-6.5Al-2Sn-4Zr-1.5Mo-2Nb-0.5Fe-0.2Si alloy is a new titanium alloy designed for such short-term high-temperature service conditions. A small amount of Fe was added to improve processing performance and reduce raw material cost. This study systematically investigated the effect of single annealing temperature on the microstructure，room temperature，and 650 ℃ tensile properties of this alloy. The experimental material was produced by triple vacuum arc remelting and rolled in α+β phase region. The original microstructure was bimodal，and the β-transus temperature （Tβ） was determined as 1010~1020 ℃. The alloy was annealed at temperatures below Tβ （950，970，990 ℃），near Tβ （1010 ℃），and above Tβ （1040 ℃） for 2 h followed by air cooling （AC）. Microstructure was characterized using optical microscopy （OM），scanning electron microscopy （SEM），electron backscatter diffraction （EBSD），and electron probe microanalysis （EPMA）. Mechanical properties were evaluated by tensile tests at room temperature and 650 ℃. Microstructure analysis showed that annealing temperature significantly influenced phase composition and microstructure. Below Tβ，Ti-6.5Al-2Sn-4Zr-1.5Mo-2Nb-0.5Fe-0.2Si alloy exhibited a bimodal structure consisting of equiaxed primary α phase （αp） and β transformed structure （βt）. As the annealing temperature increased from 950 to 990 ℃，αp size remained nearly unchanged，while its volume fraction gradually decreased. In contrast，the content and diameter of βt increased，with the change becoming more pronounced as the temperature approached Tβ. Near Tβ （1010 ℃），αp content dropped sharply to about 3%，βt size grew rapidly to 88 μm，and the secondary α lamellar （αs） thickness reached 1000 nm. Some αp particles were located inside β grains. Above Tβ （1030 ℃），αp disappeared and a fully lamellar structure formed，characterized by coarse prior β grains and basket-weave α lamellar with specific orientation relationships between lamellar of different types. EPMA results indicated that the contents of β-stabilizing elements Mo，Nb，and Fe in αp phase were significantly lower than in βt structure. Compared with Nb，Mo and Fe exhibited more pronounced segregation，with very low contents in αp phase. As the annealing temperature increased，Al content in βt structure gradually rose，while the contents of Mo，Nb，and Fe generally showed a decreasing trend. Consequently，the stability of β phase decreased，leading to a tendency to form thicker αs laths during the AC process. Tensile tests results revealed a close relationship between room temperature properties and microstructural evolution. After annealing in the range of 950~990 ℃，αp volume fraction reached or exceeded 30%，leading to excellent deformation compatibility. The elongation exceeded 20% and the reduction of area reached 53%. Meanwhile，the increase in βt size and αs lamellar thickness weakened the grain refinement strengthening effect，resulting in a slight decrease in room temperature strength with rising annealing temperature. When the annealing temperature increased to 1010 ℃ or above，the sharp reduction or disappearance of αp concentrated deformation in the lamellar structure. Dislocation slip was hindered，causing a significant deterioration in room temperature plasticity，with marked decreases in elongation and reduction of area. Analysis of 650 ℃ tensile properties showed that with increasing annealing temperature，both yield strength and tensile strength continuously rose，while elongation gradually decreased. After annealing at 950~990 ℃，the increased αs lath thickness reduced the number of interfaces that were easy to migrate at high temperature，leading to a slight increase in strength and a decrease in ductility. After annealing at 1010 ℃ or above，the disappearance of αp and the significant coarsening of β grains reduced the number of grain boundaries，further enhancing high-temperature strength. However，the poor deformation compatibility of the lamellar structure caused a sharp drop in high-temperature ductility. Comparison showed that Ti-6.5Al-2Sn-4Zr-1.5Mo-2Nb-0.5Fe-0.2Si alloy annealed at 1010 ℃ for 2 h AC achieved a better balance of comprehensive properties：its 650 ℃ tensile strength reached 555 MPa while room temperature elongation remained at 13%，indicating a good combination of high-temperature strength and room temperature ductility. Fracture analysis further illustrated the influence of annealing temperature and microstructure on fracture behavior. At room temperature，the fracture morphology changed from deep dimples （ductile） to cleavage steps （quasi-cleavage/cleavage） with varying microstructure. The fracture mode shifted from ductile fracture （990 ℃） to quasi-cleavage fracture （1010 ℃） and then to cleavage fracture （1040 ℃）. At 650 ℃，all specimens exhibited ductile fracture. However，in the fully lamellar structure （1040 ℃），a rock-candy-like fracture feature was observed due to crack propagation along β grain boundaries. In summary，by adjusting the single annealing temperature，the content of αp，the size of β grains，and the morphology of α lamellar in Ti-6.5Al-2Sn-4Zr-1.5Mo-2Nb-0.5Fe-0.2Si alloy could be effectively controlled，thereby optimizing the balance between room temperature and high-temperature properties. This study demonstrated that annealing near Tβ （e.g.，1010 ℃） could reconcile room temperature ductility with short-term high-temperature strength in this kind of alloy.
quote
| GB/T 7714-2015 | [1] Mingyu Zhao, Xiaoyun Song, Yumeng Luo, et al. Single Annealing on Microstructure and Mechanical Properties of a Short-Term High-Temperature Titanium Alloy[J]. Chinese Journal of Rare Metals, 2026, 50(3): 357-365. DOI:10.13373/j.cnki.cjrm.XY20030037. |
| MLA | [1] Mingyu Zhao, et al., "Single Annealing on Microstructure and Mechanical Properties of a Short-Term High-Temperature Titanium Alloy." Chinese Journal of Rare Metals, vol. 50, no. 3, 2026, pp. 357-365, https://doi.org/10.13373/j.cnki.cjrm.XY20030037. |
| APA | [1] Mingyu Zhao, Xiaoyun Song, Yumeng Luo, Yang Yu, Wenjing Zhang, & Wenjun Ye. (2026). Single Annealing on Microstructure and Mechanical Properties of a Short-Term High-Temperature Titanium Alloy. Chinese Journal of Rare Metals, 50(3), 357-365. https://doi.org/10.13373/j.cnki.cjrm.XY20030037 |
| IEEE | [1] Mingyu Zhao, Xiaoyun Song, Yumeng Luo, Yang Yu, Wenjing Zhang, and Wenjun Ye, "Single Annealing on Microstructure and Mechanical Properties of a Short-Term High-Temperature Titanium Alloy," Chinese Journal of Rare Metals, vol. 50, no. 3, pp. 357-365, 2026, doi: 10.13373/j.cnki.cjrm.XY20030037. keywords: {high temperature titanium alloy;Fe element;annealing treatment;microstructure;mechanical properties} |