1. Institute of Metal Research, Chinese Academy of Sciences, Shenyang 110016, China 2. School of Materials Science and Engineering, University of Science and Technology of China, Shenyang 110016, China 3. Unit 96901 of the Chinese People's Liberation Army, Beijing 100094, China
Cite this article:
CHENG Chao,CHEN Zhiyong,QIN Xushan,LIU Jianrong,WANG Qingjiang. Microstructure, Texture and Mechanical Property ofTA32 Titanium Alloy Thick Plate. Acta Metall Sin, 2020, 56(2): 193-202.
TA32 alloy is a new near α titanium alloy designed by optimizing the alloy elements ratio based on a series of elements Ti-Al-Sn-Zr-Mo-Si-Nb-Ta which has less β-stabilizing elements. This alloy has an excellent match of heat resistance and heat stability at 550 ℃, and good short-term mechanical properties at 600~650 ℃. TA32 titanium alloy thick plate can be applied to the key components in high temperature service of the hypersonic vehicle. Due to the low deformation degree of thick plate during rolling process, the heterogeneity of microstructure, texture and mechanical properties of the thick plate increases. In order to provide theoretical basis and experimental basis for the subsequent optimization of mechanical properties of TA32 titanium alloy thick plate, the microstructure, texture and mechanical properties of this alloy with a thickness of 60 mm are investigated in this work. Results show that the microstructure of the as-received material is mainly composed of lamellar α grains with few retained thin β layers, and the microstructure difference is not obvious from the surface to the center along the thickness direction of the plate no matter of the RD (rolling direction)-ND (normal direction) plane or the TD (transverse direction)-ND plane. Moreover, the rolling streamline can be obviously observed on the two planes. The morphology of α grains of the alloys presents either straight or wavy depending on their orientations with respect to the principal rolling directions. XRD results show that the as-received material has a typical T-type texture with c-axis of α phase approximately parallel to TD. At the same time, the <$10\bar{1}0$> poles are parallel to RD while <$10\bar{1}1$> poles present random distribution. As the c-axis gradually deviates from the TD of the surface to the center along the thickness direction of the plate, the Schmidt factors gradually increase, which is one of the main reasons for the gradual decrease of tensile strength; and the decrease of fraction of intragranular substructure from the surface to the center along the thickness direction is another important factor. The tensile properties have no obvious difference along the TD and RD at the same thickness position of the as-received material, but slightly worse along the ND. In addition, the influences of microstructure and texture on tensile properties are further clarified by adding two sets of heat treatment experiments (920 ℃, 30 min, AC+600 ℃, 5 h, AC; 950 ℃, 30 min, AC+600 ℃, 5 h, AC). The results show that the texture is the main factor affecting the tensile strength of TA32 titanium alloy plate at different positions under the condition of no obvious difference in microstructure. After double annealing, microstructure difference is the main factor affecting tensile strength.
Fig.3 The pole figure (PF) distributions of TA32 thick plate
Direction
Position
Rp0.2 / MPa
Rm / MPa
A / %
Z / %
TD
Surface
949
1026
16.0
29.5
1/4
941
1004
14.0
19.0
1/2
924
982
12.5
19.5
RD
Surface
964
1034
12.0
30.5
1/4
935
1002
13.8
26.0
1/2
915
983
13.8
23.0
ND
-
920
996
9.4
18.5
Table 1 Tensile properties at room temperature of TA32 thick plate
Fig.4 Macro (a~c) and fracture (d~f) morphologies of the fracture TA32 thick plate along RD (a, d), TD (b, e) and ND (c, f)
Fig.5 SEM images of fracture morphologies of the TA32 thick plate along RD (a), TD (b) and ND (c, d)
Fig.6 Microstructures of straight α colonies (a) and wavy α colonies (b) of TA32 thick plate
Fig.7 Relationship between morphology of α grains and their corresponding crystal orientation(a) inverse pole figure (IPF) map (b) PF of the corresponding dashed areas in Fig.7a
Fig.8 Schematics of fracturing of α colony along tensile direction (a) and vertical to tensile direction (b)
Fig.9 Schmidt factor (SF) distribution of two slip systems (prismatic and basal <a> slips) as a function of θ (θ—angle between c-axis and loading axis)
Fig.10 PF maps (a, d) and Schmidt factor maps (b, c, e, f) at the surface (a~c) and 1/2 thickness (d~f) (Insets in Figs.10b, c, e and f show the volume fraction distributions of SF)
Fig.11 Local misorientation (LM) results of TA32 titanium alloy thick plate at the surface (a) and 1/2 thickness (b) (Insets show the volume fraction distributions of LM)
Fig.12 Microstructures of TD-ND plane of TA32 thick plate after the heat treatment of 920 ℃ (a) and 950 ℃ (b)
Fig.13 The (0002) PF distributions of TA32 thick plate after heat treatment
Heat treatment
Position
Rp0.2 / MPa
Rm / MPa
A / %
Z / %
920 ℃, 30 min, AC+
Surface
934
1002
12.0
28.8
600 ℃, 5 h, AC
1/4
927
996
13.0
23.0
1/2
931
998
12.0
20.6
950 ℃, 30 min, AC+
Surface
908
976
17.0
19.1
600 ℃, 5 h, AC
1/4
913
985
14.0
24.5
1/2
907
971
12.6
21.7
Table 2 Room temperature tensile properties of TA32 thick plate after heat treatment
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