低密度Ti2AlNb基合金热轧板微观组织的热稳定性
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Thermal Stability of Microstructures in Low-Density Ti2AlNb-Based Alloy Hot Rolled Plate
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通讯作者: 曲寿江,qushoujiang@tongji.edu.cn,主要从事TiAl、Ti2AlNb基合金精密热成型及钛基合金增材制造的研究陈道伦,dchen@torontomu.ca,主要从事先进材料和关键工程材料的变形、疲劳、断裂、焊接和连接的研究
责任编辑: 肖素红
收稿日期: 2021-07-30 修回日期: 2022-05-09
基金资助: |
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Corresponding authors: QU Shoujiang, associate professor, Tel:
Received: 2021-07-30 Revised: 2022-05-09
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作者简介 About authors
冯艾寒,女,1974年,副教授
采用OM、SEM、XRD和TEM研究了低密度Ti2AlNb基合金热轧板在600~1100℃保温12 h微观组织的热稳定性。结果表明,Ti2AlNb基合金原始态热轧板主要由α2、B2以及O相组成,颗粒状的α2相分布在B2相基体中。Ti2AlNb基合金热轧板600℃保温12 h,颗粒状的α2相分布在B2相基体中,B2相基体中分布着大量细小的O相板条。随着温度的升高,合金热轧板800~900℃保温12 h的微观组织由α2、B2以及O相三相构成,α2相颗粒逐渐球化,O相板条粗化并固溶于B2相基体中。当温度升高至950℃时,B2相基体中的O相板条消失。合金热轧板在950~1000℃保温12 h形成α2 + B2两相区,α2相颗粒球化并趋向于分布在B2相基体的晶界处。当温度升高至1100℃时,合金基体为B2单相,B2晶界处分布着极少量的残留α2相颗粒。Vickes显微硬度分布结果显示,随着温度的升高,合金板材在600℃时硬度达到峰值(509 HV),这与大量细小的O相板条有关。
关键词:
Multielement and multiphase intermetallic alloys based on an ordered orthorhombic (O) phase Ti2AlNb, where the presence of a long-range order superlattice structure effectively impedes the movement of dislocations and high-temperature diffusion, are a class of highly promising lightweight high-temperature structural materials for aerospace applications due to their high specific strength and superior fracture toughness. Thermal stability of microstructures in the hot rolled sheet of a low-density Ti2AlNb-based alloy has been investigated in a temperature range from 600oC to 1100oC for 12 h via OM, SEM, XRD, and TEM/STEM. The results showed that the initial Ti2AlNb-based alloy hot rolled sheet consisted of α2, B2, and O phases. Furthermore, the Ti2AlNb-based alloy hot rolled sheet at 600oC for 12 h consisted of α2, B2, and O phases, where the particle shaped α2 phase was distributed in the B2 matrix, and lath-like O phase lay inbetween the α2 particles. The spheroidization of the α2 phase started to occur along with the coarsening and solutionizing of the lath O phase in the B2 matrix at a temperature between 800oC and 900oC for 12 h, while the hot rolled Ti2AlNb-based alloy plate was still composed of α2, B2, and O phases. When the temperature reached 950oC, the O phase disappeared in the B2 matrix. Only α2 + B2 two phases were present in the hot rolled Ti2AlNb-based alloy at 950-1000oC for 12 h, where the α2 phase was spheroidized and tended to distribute surrounding B2 grain boundaries. When the temperature rose to 1100oC, the alloy contained a B2 single phase with only some residual α2 phase. Moreover, the Vickers microhardness contour vs temperature plot revealed that a peak hardness of as high as 509 HV appeared at 600oC due to the presence of numerous fine O laths.
Keywords:
本文引用格式
冯艾寒, 陈强, 王剑, 王皞, 曲寿江, 陈道伦.
FENG Aihan, CHEN Qiang, WANG Jian, WANG Hao, QU Shoujiang, CHEN Daolun.
Ti2AlNb基合金铸态组织粗大、室温塑性较低、高温变形抗力大,一般通过等温锻造、包覆精密轧制等热加工过程细化组织[18,19],随后的热处理有助于微观组织调制[3,20]与力学性能精确控制[21]。Ti2AlNb基合金通过热加工可以获得等轴、双态和层片状等典型的显微组织[22,23]。在O + B2相区高温区间对经过热变形的合金进行固溶或时效处理,之后快速冷却,可获得等轴状两相组织,O相含量随热处理温度的升高而降低[24]。在1025℃固溶处理,可保留8%~12% (体积分数)弥散分布的α2相,从而有效阻碍B2相在高温固溶过程中长大,随后在O + B2双相低温区间时效处理获得双态组织[25]。
不同微观组织的Ti2AlNb基合金表现出不同的性能特征。双态组织塑性和抗疲劳性能较好,具有中等的抗蠕变性能;等轴状组织的合金抗蠕变性能和室温断裂韧性较差;层片状组织的合金具有优良的断裂韧性和抗蠕变性能,但塑性较差[26,27]。由于晶粒尺寸对合金蠕变及拉伸性能的影响规律相反,合金的微观组织难以同时满足对强度、塑性及蠕变的共同要求。Ti2AlNb基合金板条组织比等轴组织具有更高的蠕变性能,这是由于粗大的O相板条有利于提高合金蠕变性能;细小的针状O + B2双相组织的强度和塑性都较好[28]。研究[29]表明,O相层片对合金的强化作用与其尺寸、含量相关,可通过对片层O相尺寸和含量的控制实现合金强度与塑性的良好匹配。因此,根据Ti2AlNb基合金的相变规律和使役条件进行微观组织优化设计,可以促进Ti2AlNb基合金的实用化进程[3]。
本工作在Ti2AlNb基合金成分设计过程中引入了“Nb当量”的概念,即用强β稳定元素(Mo、V和Si)部分替代Nb元素,设计开发了低密度Ti2AlNb基合金,其密度约为5.3 g/cm3。主要研究低密度Ti2AlNb基合金热轧板微观组织的热稳定性:(1) 合金在600~1100℃保温12 h的相转变规律;(2) 合金硬度随组织演变的规律。旨在揭示Ti2AlNb基合金相变与硬度变化规律,从而实现合金微观组织与力学性能精确调控。
1 实验方法
采用名义成分为Ti-22Al-23(Nb, Mo, V, Si)的Ti2AlNb基合金热轧板为研究对象,合金热轧板经过3次真空自耗电弧熔炼、热等静压、多向等温锻造和包覆精密热轧制及中间热处理等技术制备,热轧板厚度为2.5 mm。将Ti2AlNb基合金热轧板线切割为尺寸10 mm × 8 mm × 2.5 mm的矩形试样,样品长度方向与轧向平行。采用不同粒度的金刚石砂纸打磨样品,酒精清洗吹干后用真空石英管密封。热处理温度分别为600、800、850、900、950、1000、1050和1100℃,保温12 h,随后迅速打破石英管水淬,以保留高温时的组织特征。
样品经过金刚石砂纸打磨后,采用6%HClO4 + 34%CH3(CH2)3OH + 60%CH3OH (体积分数)的电解液,在-30℃条件下电解抛光。金相样品电解抛光后采用Kroll试剂腐蚀,利用DM4000M光学金相显微镜(OM)和Quanta 200 FEG场发射扫描电子显微镜(SEM)进行微观组织观察。采用Dmax2500 X射线衍射仪(XRD)进行物相分析。透射电镜(TEM)样品采用电火花线切割机切取厚度为0.5 mm的样品,利用砂纸将试样表面磨至70 μm厚,采用MTP-1A型磁力驱动双喷电解减薄器在液氮冷却条件下(-30℃)双喷减薄,电解液为6%HClO4 + 34%CH3(CH2)3OH + 60%CH3OH (体积分数)。利用Tecnai G2 F30型TEM观察样品的微观组织。Vickers硬度测试采用HVS-1000A型数显显微硬度计,载荷为4.903 N,保压时间为15 s,每个样品测量10次,计算样品的平均值和方差。
2 实验结果
2.1 Ti2AlNb基合金热轧态及热处理态组织形貌
图1
图1
Ti2AlNb基合金原始态热轧板显微组织和选区电子衍射(SAED)花样
(a) OM image (b) SEM image (c) STEM image (d) TEM image
(e-g) SAED patterns of points I (e), II (f), and III (g) in Fig.1d, respectively
Fig.1
Microstructures and selected area electron diffraction (SAED) patterns of hot rolled Ti2AlNb-based alloy plate
图2为Ti2AlNb基合金热轧板在不同温度保温12 h水淬后的OM像。可见,600℃热处理时,合金中白色相为α2相,基体为B2相。当温度升高至800℃时,可以观察到少量的颗粒状α2相,B2相基体中析出大量细小的板条相。当温度继续升高到900℃时,仍可以观察到少量的颗粒状α2相,而B2相基体中的板条相逐渐消失。当温度升高到950~1000℃时,B2相基体中颗粒状的α2相开始球化且含量逐渐减少,板条相消失。当温度升高至1100℃时,合金基本为B2相单相,晶粒呈六角形,平均晶粒尺寸大于200 μm。
图2
图2
Ti2AlNb基合金热轧板在不同温度保温12 h水淬后的OM像
Fig.2
OM images of hot rolled Ti2AlNb-based alloy plate after heat treatment at 600oC (a), 800oC (b), 900oC (c), 950oC (d), 1000oC (e), and 1100oC (f) for 12 h and then water quenching
图3为不同温度保温12 h水淬后Ti2AlNb基合金的SEM像。可见,600℃保温12 h后,B2相基体中分布着黑色颗粒状的α2相,由于受SEM的分辨率限制,图3a中黑色α2相和B2相基体中是否有O相分布尚需进一步通过TEM观察确认。当温度升高至800℃时,可以观察到黑色颗粒状的α2相,EDS结果显示,白色B2相基体中析出大量灰色板条状O相。当温度继续升高到900℃时,仍可以观察到颗粒状α2相,板条状O相在B2相基体中逐渐消失。当温度升高到950~1000℃,合金B2相基体中分布着颗粒状的α2相,O相板条消失,随温度升高,α2相球化且含量减少。当温度升高至1100℃时,合金主要为B2相单相,只有极少量的残余α2相颗粒分布在B2相基体的三角晶界处,B2相的晶粒尺寸大于200 μm。
图3
图3
Ti2AlNb基合金热轧板在不同温度保温12 h水淬后的SEM像
Fig.3
SEM images of hot rolled Ti2AlNb-based alloy plate after heat treatment at 600oC (a), 800oC (b), 900oC (c), 950oC (d), 1000oC (e), and 1100oC (f) for 12 h and then water quenching
图4
图4
Ti2AlNb基合金热轧板在不同温度保温12 h前后的XRD谱
Fig.4
XRD spectra of hot rolled Ti2AlNb-based alloys plate before (a) and after heat treatment at 600oC (b), 800oC (c), 850oC (d), 900oC (e), 950oC (f), 1000oC (g), 1050oC (h), and 1100oC (i) for 12 h and then water quenching (Insets in Figs.4c-e show the magnified spectra)
图5
图5
Ti2AlNb基合金热轧板600℃保温12 h水淬的TEM像、STEM像和SAED花样
Fig.5
TEM (a) and STEM (b) images of hot rolled Ti2AlNb-based alloy plate after heat treatment at 600oC for 12 h and then water quenching, and corresponding SAED patterns of points I (c) and II (d) in Fig.5a
图6
图6
Ti2AlNb基合金热轧板850℃保温12 h水淬的TEM像、STEM像和SAED花样
Fig.6
TEM (a) and STEM (b) images of hot rolled Ti2AlNb-based alloy plate after heat treatment at 850oC for 12 h and then water quenching, and corresponding SAED patterns of points I (c), II (d), III (e), and IV (f) in Fig.6b
图7
图7
Ti2AlNb基合金热轧板900℃保温12 h的TEM像和SAED花样
Fig.7
TEM image (a) of hot rolled Ti2AlNb-based alloy plate after heat treatment at 900oC for 12 h and then water quenching, and corresponding SAED patterns of points I (b), II (c), and III (d) in Fig.7a
图8为Ti2AlNb基合金热轧板1000℃保温12 h水淬后的TEM像、STEM像和SAED花样。可见,Ti2AlNb基合金在1000℃处于α2 + B2两相区。
图8
图8
Ti2AlNb基合金热轧板1000℃保温12 h水淬的TEM像、STEM像和SAED花样
Fig.8
TEM (a) and STEM (b) images of hot rolled Ti2AlNb-based alloy plate after heat treatment at 1000oC for 12 h and then water quenching, and corresponding SAED patterns of points I (c), II (d), III (e), and IV (f) in Fig.8a
2.2 Ti2AlNb基合金显微硬度
图9显示了Ti2AlNb基合金热轧板Vickers硬度随热处理温度的变化。Ti2AlNb基合金原始态热轧板由α2、B2和O相组成,脆性的α2相颗粒分布在塑性B2相基体中,因而,合金热轧板硬度较低(341 HV)。600℃保温12 h后,α2相颗粒中也有条纹状的O相,B2相基体中析出大量细小的O相板条,硬度达到峰值(509 HV)。随着温度升高,在800℃保温12 h时,合金B2相基体中O相板条粗化并逐渐固溶于基体中,使合金硬度逐渐降低。合金热轧板900℃保温12 h后,硬度降低至342 HV。随着温度继续升高,O相固溶于B2相基体中,且α2相球化并逐渐溶于B2基体中,合金化元素Nb、Mo、V、Si等固溶于B2相基体中,在固溶强化的作用下合金的硬度逐渐提高。
图9
图9
Ti2AlNb基合金热轧板Vickers硬度随热处理温度的变化
Fig.9
Microhardnesses of hot rolled Ti2AlNb-based alloy plate as a function of heat treatment temperature
3 分析与讨论
表2 Ti2AlNb基合金热轧板不同温度热处理前后的相组成
Table 2
Heat treatment | Phase constituent | ||
---|---|---|---|
XRD | SEM | TEM | |
As-rolled | B2 + O + α2 | B2 + O + α2 | B2 + α2 |
600oC, 12 h, WQ | B2 + O + α2 | B2 + O + α2 | B2 + O + α2 |
800oC, 12 h, WQ | B2 + O + α2 | B2 + O + α2 | - |
850oC, 12 h, WQ | B2 + O + α2 | B2 + O + α2 | B2 + O + α2 |
900oC, 12 h, WQ | B2 + O + α2 | B2 + O + α2 | B2 + O + α2 |
950oC, 12 h, WQ | B2 + α2 | B2 + α2 | - |
1000oC, 12 h, WQ | B2 + α2 | B2 + α2 | B2 + α2 |
1050oC, 12 h, WQ | B2 + α2 | B2 + α2 | - |
1100oC, 12 h, WQ | B2 + α2 | B2 + α2 | - |
Popov等[32]研究表明,47.6Ti-24.3Al-24.8Nb-1.0Zr-1.4V-0.6Mo-0.3Si合金在700~750℃保温1 h后水冷的微观组织为β + O相,800~950℃时为α2 + B2/β + O三相,1000℃时为B2 + α2双相组织,1050℃时为β单相。Kazantseva和Lepikhin[33]研究Ti-22Al-26.6Nb合金相变特征时,在1100℃观察到α2 + B2/β + O三相共存组织。由此可见,不同成分Ti2AlNb基合金相变趋势相似,相变点因合金成分和热处理制度而变化。900~950℃之间O相发生了转变,1050~1100℃之间α2相发生了α2→B2的转变。
4 结论
(1) Ti2AlNb基合金原始态热轧板由O、B2和α2相组成,颗粒状的α2相分布在B2相基体中。
(2) Ti2AlNb基合金热轧板在600℃保温12 h时,颗粒状的α2相分布在B2相基体中,α2相颗粒中有少量条纹状的O相,B2相基体中分布着大量细小的O相板条。随着热处理温度升高,800~900℃保温12 h时,合金组织由α2、B2以及O相相构成,α2相颗粒逐渐球化,O相板条粗化并固溶于B2相基体中。当温度升高至950℃时,B2相基体中O相板条消失。合金热轧板在950~1000℃时形成α2 + B2两相区,α2相颗粒球化并趋向于分布在B2相基体的晶界处。当温度升高至1100℃时,合金热轧板基体为B2单相,B2晶界处分布着极少量的残留α2相颗粒。
(3) Vickers显微硬度分布结果表明,Ti2AlNb基合金热板材在600℃时硬度达到峰值(509 HV),这与大量细小的O相板条有关。
参考文献
A new ordered orthorhombic phase in a Ti3Al-Nb alloy
[J].
Superplastic behavior of the fine-grained Ti-21Al-18Nb-1Mo-2V-0.3Si intermetallic alloy
[J].
High temperature oxidation behavior of as-rolled Ti2AlNb-based alloy
[J].
Ti2AlNb基合金轧板高温抗氧化性能研究
[J].
Thermodynamic and microstructural study of Ti2AlNb oxides at 800oC
[J].The high-temperature structural applications of Ti2AlNb-based alloys, such as in jet engines and gas turbines, inevitably require oxidation resistance. The objective of this study is to seek fundamental insight into the oxidation behavior of a Ti2AlNb-based alloy via detailed microstructural characterization of oxide scale and scale/substrate interface after oxidation at 800 degrees C using X-ray diffraction (XRD), scanning electron microscopy (SEM), electron probe microanalysis (EPMA), and transmission electron microscopy (TEM). The oxide scale exhibits a complex multi-layered structure consisting of (Al, Nb)-rich mixed oxide layer (I)/mixed oxide layer (II)/oxygen-rich layer (III)/substrate from the outside to inside, where the substrate is mainly composed of B2 and O-Ti2AlNb phases. High-resolution TEM examinations along with high-angle annular dark-field (HAADF) imaging reveal: (1) the co-existence of two types (alpha and delta) of Al2O3 oxides in the outer scale, (2) the presence of metastable oxide products of TiO and Nb2O5, (3) an amorphous region near the scale/substrate interface including the formation of AlNb2, and (4) O-Ti2AlNb phase oxidized to form Nb2O5, TiO2 and Al2O3.
Microstructure and low cycle fatigue of a Ti2AlNb-based lightweight alloy
[J].
Recent advances on Ti2AlNb-based alloys
[J].
Ti2AlNb基合金的研究进展
[J].
Recent advances on microstructural controlling and hot forming of Ti2AlNb-based alloys
[J].
Ti2AlNb基合金微观组织调制及热成形研究进展
[J].
Application of Ti2AlNb alloy electron beam welding on aero-engine casing
[J].
Ti2AlNb合金电子束焊接在航空发动机机匣中的应用
[J].
Phase transformation and microstructure control of Ti2AlNb-based alloys: A review
[J].
Electronic structure, phase stability, and cohesive properties of Ti2 XAl (X = Nb, V, Zr)
[J].
A first principles study of Ti2AlNb intermetallic
[J].
Strain localization, slip-band formation and twinning associated with deformation of a Ti-24at.%Al-11at.%Nb alloy
[J].
Microstructure and plastic deformation of orthorhombic titanium aluminides Ti2AlNb. III. Formation of transformation twins upon the B2→Ophase transformation
[J].
Microstructure and plastic deformation of orthorhombic titanium aluminides Ti2AlNb. IV. Formation of the transformation twins upon the α2→O phase transformation
[J].
High cycle fatigue at high temperatures of the lamellar microstructure of Ti-22Al-25Nb alloy
[J].
板条组织Ti-22Al-25Nb合金高温高周疲劳行为
[J].
Effect of heat treatment on microstructure and properties of cast Ti-22Al-25Nb alloy
[J].
热处理对铸造Ti2AlNb合金组织和力学性能的影响
[J].
Plate preparation, microstructure and mechanical properties of low-density Ti2AlNb-based alloys
[D].
低密度Ti2AlNb基合金板材制备及组织与力学性能研究
[D]
Research on microstructure and mechanical properties of Ti2AlNb-based alloy fabricated by multiple isothermal forging
[D].
Ti2AlNb基合金多向等温锻造组织与力学性能研究
[D].
Phase transformation and superplasticity deformation mechanism in Ti2AlNb-based alloys
[D].
Ti2AlNb基合金相变及超塑性变形机理研究
[D].
Microstructure evolution and comprehensive mechanical properties of β/B2 processed Ti-22Al-23Nb-2(Mo, Zr) alloy
[J].
β/B2锻造Ti-22Al-23Nb-2(Mo, Zr)合金的组织演化与综合力学性能
[J].
Effects of hot deformation parameters on lamellar microstructure evolution of Ti2AlNb based alloy
[J].
热变形参数对Ti2AlNb基合金片层组织演变的影响
[J].
Effect of solution temperature on microstructure of Ti-22Al-25Nb alloy
[J].
固溶温度对Ti-22Al-25Nb合金微观组织的影响
[J].
Part I. The microstructural evolution in Ti-Al-Nb O + bcc orthorhombic alloys
[J].
The phase evolution and microstructural stability of an orthorhombic Ti-23Al-27Nb alloy
[J].
Part II. The creep behavior of Ti-Al-Nb O + bcc orthorhombic alloys
[J].
Microstructure, creep, and tensile behavior of a Ti-12Al-38Nb (at.%) beta+orthorhombic alloy
[J].
Part III. The tensile behavior of Ti-Al-Nb O + bcc orthorhombic alloys
[J].
Instability of the O-phase in Ti-22Al-25Nb alloy during elevated-temperature deformation
[J].
Coherent precipitates in the b.c.c./orthorhombic two-phase field of the Ti-Al-Nb system
[J].
Transformations in a Ti-24Al-15Nb alloy: Part I. Phase equilibria and microstructure
[J].
Phase and structural transformations in the alloy on the basis of the orthorhombic titanium aluminide
[J].
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