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金属学报  2024, Vol. 60 Issue (1): 95-106    DOI: 10.11900/0412.1961.2022.00247
  研究论文 本期目录 | 过刊浏览 |
交叉包套轧制Ti-44Al-5Nb-1Mo-2V-0.2B合金的微观组织演化及力学性能
王秀琦1, 李天瑞2, 刘国怀1(), 郭瑞琪1, 王昭东1
1 东北大学 轧制技术与连轧自动化国家重点实验室 沈阳 110819
2 安徽工业大学 冶金工程学院 马鞍山 243000
Microstructure Evolution and Mechanical Properties of Ti-44Al-5Nb-1Mo-2V-0.2B Alloys in the Cross Hot-Pack Rolling Process
WANG Xiuqi1, LI Tianrui2, LIU Guohuai1(), GUO Ruiqi1, WANG Zhaodong1
1 State Key Laboratory of Rolling and Automation, Northeastern University, Shenyang 110819, China
2 School of Metallurgical Engineering, Anhui University of Technology, Maanshan 243000, China
引用本文:

王秀琦, 李天瑞, 刘国怀, 郭瑞琪, 王昭东. 交叉包套轧制Ti-44Al-5Nb-1Mo-2V-0.2B合金的微观组织演化及力学性能[J]. 金属学报, 2024, 60(1): 95-106.
Xiuqi WANG, Tianrui LI, Guohuai LIU, Ruiqi GUO, Zhaodong WANG. Microstructure Evolution and Mechanical Properties of Ti-44Al-5Nb-1Mo-2V-0.2B Alloys in the Cross Hot-Pack Rolling Process[J]. Acta Metall Sin, 2024, 60(1): 95-106.

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摘要: 

TiAl合金因其低密度、优异的高温强度、抗蠕变和抗氧化性能而在航空航天和汽车工业中具有广阔的应用前景,但其本质脆性和变形能力差的缺点严重限制其进一步发展。本工作通过交叉包套轧制(CHPR)和一步退火处理实现了800℃下超高塑性Ti-44Al-5Nb-1Mo-2V-0.2B合金板材的制备。利用SEM、EBSD、TEM和拉伸等实验方法考察了TiAl合金的热变形行为、不同轧制和热处理工艺对微观组织和力学性能的影响。结果表明,与单向包套轧制(UHPR)相比,CHPR板材沿厚度方向和板面方向均表现出更高的组织均匀性,微观组织由残余α2/γ片层及其晶界的等轴γα2和B2相组成,但残余片层的尺寸较小且含量明显降低,其原因是在CHPR的双向剪切力和压应力的作用下大量残余片层破碎并发生了完全再结晶。CHPR TiAl合金的高温流变软化机制主要包括片层弯曲扭折变形、β/B2相协调变形、α2/γ片层的相变分解、初生和二次孪晶诱导的γ相动态再结晶。随后对CHPR合金进行1200~1340℃的退火热处理,1200℃条件下获得了等轴片层和等轴晶粒(α2 + γ + B2)的多相组织,部分晶粒达到了纳米级。1340℃条件下得到了近全片层组织。对UHPR和CHPR板材的横/纵向和1200℃退火热处理试样的拉伸性能进行比较,CHPR板材横纵向的拉伸性能更加均匀,再经1200℃退火热处理后获得的多相等轴组织具有最佳的强度-塑性匹配,室温下抗拉强度为624 MPa,延伸率为1.32%;800℃下抗拉强度为515 MPa,延伸率可达107.0%。分析试样的断裂行为可知,室温下3种试样的断裂方式为穿片层和解理断裂。800℃下断裂方式转变为韧性断裂,断裂失效机制以微孔联结机制为主,其中经过1200℃退火热处理的板材断口具有更小而深的韧窝,塑性最佳。精细的片层结构和均匀细小的等轴晶组织能够阻碍裂纹的扩展,有利于综合力学性能的提高。

关键词 TiAl合金交叉包套轧制热处理微观组织力学性能    
Abstract

TiAl alloys are highly promising for high-temperature structural applications in the aerospace and automotive industries because of their low density, excellent high-temperature strength, and resistance to creep and oxidation. Nevertheless, low-temperature brittleness and poor deformability are the main factors severely restricting the widespread application of TiAl alloys. The process of β-solidifying γ-TiAl alloys results in alloys that consist primarily of α2, γ, and B2 phases, and have superior hot workability. Further thermomechanical treatments are applied to achieve a fine microstructure and enhance the inherent ductility of γ-TiAl alloys. In this work, Ti-44Al-5Nb-1Mo-2V-0.2B alloy sheet with ultrahigh plasticity at 800oC was achieved by cross hot-pack rolling (CHPR) and one-step annealing processes. SEM, EBSD, TEM, and tensile methods were used to investigate the hot deformation behavior, and the effects of different rolling processes and heat treatments on the microstructural evolution and mechanical properties of the alloy. The results show that the CHPR sheet had a more highly uniform deformation microstructure along the thickness direction and sheet plane compared with that of a unidirectional hot-pack rolled (UHPR) sheet, which consisted of residual lamellar colonies and equiaxed γ, α2, and B2 grains at colony boundaries. The size of the residual lamellar colonies was significantly smaller and the content was lower in the CHPR sheet compared with the UHPR sheet. This was due to a large number of broken residual lamellae and complete recrystallization under the combined action of a bidirectional shear force and compressive stress during the CHPR process. The high-temperature flow-softening mechanisms of TiAl alloy in the CHPR process mainly included bending and kinked lamellae, β/B2 coordinated deformation, phase-transformation decomposition of α2/γ lamellar, and dynamic recrystallization induced by primary and secondary twinning. To achieve further grain refinement, subsequent annealing of the CHPR-processed TiAl alloy was performed at 1200-1340oC. A multiphase equiaxed microstructure with fine lamellar colonies was obtained at 1200oC and a nearly complete lamellar microstructure was obtained at 1340oC. Moreover, the room-temperature and high-temperature tensile properties of UHPR and CHPR sheets in the horizontal and vertical directions were compared with samples annealed at 1200oC. The tensile properties of the CHPR sheets were more uniform in both directions. The multiphase equiaxed microstructure obtained in the CHPR alloy annealed at 1200oC had the best strength-plasticity balance with a tensile strength of 624 MPa (515 MPa) and elongation of 1.32% (107.0%) at room temperature (800oC). According to the fracture behavior, the fracture mode of these alloy sheets was translamellar or cleavage fracture at room temperature. Conversely, the fracture mode changed to ductile fracture at 800oC, and the failure mechanism was mainly via microhole coupling. The fractures in the annealed sheets (1200oC) had small and deep dimples, indicating optimal tensile elongation. The uniform and fine lamellar structure and equiaxed microstructure can hinder crack propagation and achieve enhanced mechanical properties.

Key wordsTiAl alloy    cross hot-pack rolling    heat treatment    microstructure    mechanical property
收稿日期: 2022-05-18     
ZTFLH:  TG146  
基金资助:国家自然科学基金项目(52071065);中央高校基本科研业务费基金项目(N2007007)
通讯作者: 刘国怀,liugh@ral.neu.edu.cn,主要从事先进结构材料及高温合金的热加工和热处理技术的研究
Corresponding author: LIU Guohuai, associate professor, Tel: (024)83686739, E-mail: liugh@ral.neu.edu.cn
作者简介: 王秀琦,男,1997年生,硕士生
图1  Ti-44Al-5Nb-1Mo-2V-0.2B (TNM-VB)合金的交叉包套轧制工艺示意图
图2  TNM-VB合金铸态和均匀化热处理后的微观组织
图3  单向和交叉包套轧制TNM-VB板材的宏观形貌
图4  单向和交叉包套轧制TNM-VB合金板材沿厚度方向的微观组织
图5  单向和交叉包套轧制TNM-VB合金板材沿板面方向的微观组织
图6  单向和交叉包套轧制TNM-VB合金的热变形组织
图7  交叉包套轧制TNM-VB合金热变形组织的EBSD分析及晶粒取向角分布
图8  交叉包套轧制TNM-VB合金在不同温度下退火热处理的微观组织
SpecimenDirectionRT800oC
UTS / MPaδ / %YS / MPaUTS / MPaδ / %
Homogenized treatment6030.145156204.1
UHPRTD7540.89460593100.4
RD7370.3245856874.1
CHPRRD17490.4842258265.6
RD27561.1645854160.8
Annealing treatment (1200oC)RD26241.32424515107.0
Annealing treatment (1240oC)RD26341.0642452180.4
表1  TNM-VB合金在不同轧制和退火热处理工艺下室温和800℃的拉伸性能
图9  不同轧制和退火热处理工艺下TNM-VB合金的室温和高温拉伸断口形貌
图10  不同轧制和退火热处理工艺下TNM-VB合金的室温和高温拉伸断口附近组织
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