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Acta Metall Sin  2020, Vol. 56 Issue (7): 979-987    DOI: 10.11900/0412.1961.2019.00388
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Microstructure and Tensile Properties of Ti-43.5Al-4Nb-1Mo-0.1B Alloy Processed by Hot Canned Extrusion
LIU Xianfeng1,2, LIU Dong1(), LIU Renci1, CUI Yuyou1, YANG Rui1
1. Institute of Metal Research, Chinese Academy of Sciences, Shenyang 110016, China
2. College of Materials Science and Engineering, University of Science and Technology of China, Shenyang 110016, China
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Abstract  

β solidifying γ-TiAl alloys are being considered for high-temperature application in the aerospace and automotive industries as high efficiency materials which can withstand temperatures up to 800 ℃ and owns attractively thermal and mechanical properties. Through thermos-mechanical process can obtain excellent alloy properties, such as high strength and better elongation. But it will cause anisotropy. Ti-43.5Al-4Nb-1Mo-0.1B alloy rectangular bar was prepared by isothermal hot canned extrusion process. The OM, SEM, XRD, TEM and tensile methods were used to study the microstructure and tensile properties of the rectangular rods in different states and locations. The results show that the extruded structure of the rectangular rods is relatively uniform and there is no significant difference in the microstructure at different locations. The extrusion deformation makes the orientation of the lamellar uniform, tending to be parallel to the extrusion direction; γ phase in the grain boundary exists in the three forms of graininess, bulk and strip; the β phase is shredded during extrusion and is elongated in a parallel extrusion direction. Under the TEM observation, lamellar at the edge of the bar was completely shredded, and lamellar at the core position was elongated after lamellar was broken. A large number of ω0 phases are generated in the β0 phase, and the phase relationship of the two follows: [111ˉ]β0//[0001]ω0, {110}β0//{21ˉ1ˉ0}ω0. The tensile strength reaches 1000 MPa or more and elongations are about 0.5% of the rectangular bar at room temperature; the yield strength is above 400 MPa at 800 ℃, which exhibits remarkable plasticity. After the ageing treatment of the hot extruded alloy, a large amount of lens-shape γ phase is formed in the β0 phase, and the ageing treatment improves the high temperature tensile properties of the alloy, but the ω0 phase can not be eliminated.

Key words:  β solidifying      γ-TiAl alloy      hot canned extrusion      deformation microstructure      tensile property     
Received:  13 November 2019     
ZTFLH:  TG146.2  
Fund: National Natural Science Foundation of China(51701209)
Corresponding Authors:  LIU Dong     E-mail:  dliu@imr.ac.cn

Cite this article: 

LIU Xianfeng, LIU Dong, LIU Renci, CUI Yuyou, YANG Rui. Microstructure and Tensile Properties of Ti-43.5Al-4Nb-1Mo-0.1B Alloy Processed by Hot Canned Extrusion. Acta Metall Sin, 2020, 56(7): 979-987.

URL: 

https://www.ams.org.cn/EN/10.11900/0412.1961.2019.00388     OR     https://www.ams.org.cn/EN/Y2020/V56/I7/979

Cast ingotTiAlNbMoBFeSiCNHO
NominalBal.43.54.001.000.100------
ActualBal.43.23.941.030.076≤0.051≤0.15≤0.00680.020.0570.013
Table 1  Chemical compositions of the Ti-43.5Al-4Nb-1Mo-0.1B (TNM) alloy
Fig.1  BSE-SEM image (a) and XRD spectrum (b) of as-cast TNM alloy (Dotted lines in Fig.1a show the larnellar orientations)
ConditionMicrostructure(α2+γ) colonyLamellarKinkingβ phaseγ phase
typeorientationlamellarvolumeform
LengthWidthRatio
(°)fraction / %
μmμm
As-castNear lamellar82.3352.901.610~180No0.58Graininess
As-extrusion,Near lamellar177.8941.084.260~30, mainYes14.46Graininess,
edgebulk, strip
As-extrusion,Near lamellar204.1350.674.030~30, mainYes15.43Graininess,
centerbulk, strip
Ageing,Near lamellar178.3240.784.370~30, mainYes<10.83Graininess, bulk,
edgestrip, lens-shape
Ageing,Near lamellar210.5651.464.090~30, mainYes<8.83Graininess, bulk,
centerstrip, lens-shape
Table 2  Microstructural characteristics of TNM alloy in different conditions
Fig.2  BSE-SEM images of microstructure of edge (a, c) and center (b, d) partitions of extrusion (a, b) and ageing (c, d) TNM alloys
Fig.3  Bright field TEM image (a) and SAED pattern (b) of graininess γ phase in grain boundary, and BSE-SEM images of bulk (c) and strip (d) γ phases
Fig.4  Dark field TEM image of ω0 phase (a) and SAED pattern showing relationships of ω0 and β0 phases (b)
Fig.5  Low-magnification corrosion-morphology of longitudinal section of extruded TNM alloy
Fig.6  Bright field TEM images of edge (a) and center (b) partitions of extruded TNM alloy
Fig.7  Bright field TEM image (a) and SAED pattern (b) of γ phase precipitated from β0 phase during ageing treatment
Fig.8  Tensile properties of γ-TiAl alloy (a) and tensile strain-stress curves of samples in different conditions of TNM alloy (b) at room temperature (Extr.—extrusion, HIP—hot isostatic pressing)
Fig.9  Fracture surfaces (a, b), corresponding BSE-SEM images (c, d) and crack nucleation details (e, f) of samples of edge (a, c, e) and center (b, d, f) positions of extrusion-ageing TNM alloy
Fig.10  Tensile properties of γ-TiAl alloy (a) and tensile strain-stress curves of samples in different conditions of TNM alloy (b) at 800 ℃
Fig.11  Fracture morphology in edge partition of ageing-extrusion TNM alloy at 800 ℃
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