Mechanical Properties and Electrical Conductivity of α + β Titanium Alloy Sheet Regulated by Heat Treatment
ZHANG Shuqian1,2, MA Yingjie2(), WANG Qian2, QI Min1,2, HUANG Sensen2, LEI Jiafeng2, YANG Rui2
1 School of Materials Science and Engineering, University of Science and Technology of China, Shenyang 110016, China 2 Shi -changxu Innovation Center for Advanced Materials, Institute of Metal Research, Chinese Academy of Sciences, Shenyang 110016, China
Cite this article:
ZHANG Shuqian, MA Yingjie, WANG Qian, QI Min, HUANG Sensen, LEI Jiafeng, YANG Rui. Mechanical Properties and Electrical Conductivity of α + β Titanium Alloy Sheet Regulated by Heat Treatment. Acta Metall Sin, 2024, 60(12): 1622-1636.
Eddy current loss, which produces Joule heat and reduces transmission efficiency, is inevitable when the magnetic coupling is running. Magnetic couplings with high electrical resistivity alloys, such as titanium alloy, have been proven to be effective in suppressing the eddy currents. The Ti-6Al-3Mo-2V-1Cr-2Sn-2Zr alloy sheet was a α + β titanium alloy for marine engineering with high specific strength and electrical resistivity, which was used in magnetic couplings to suppress the eddy currents. In this study, the effect of annealing temperature on the microstructure, mechanical properties, and electrical conductivity of the Ti-6Al-3Mo-2V-1Cr-2Sn-2Zr alloy sheet was investigated. The results revealed that the band structure was arranged along the rolling direction (RD), and the as-rolled titanium alloy sheet showed a typical T-type texture with the c-axis of the α phase approximately parallel to the transverse direction (TD). A considerable increase in tensile strength and decrease in elongation after α ＋ β region (850-920oC) annealing was thought to result from the strengthening of secondary α/β interfaces in the bimodal structure. Simultaneously, the α phase showed both T-type and R-type textures, which also resulted in higher yield strength along the TD of the sheet. Additionally, when the sheet suffered a β phase region annealing (950-1000oC), the elongation immediately decreased due to the coarseness and precipitation of the secondary α and grain boundary α phases, respectively. Meanwhile, the annealed sheet showed an R-type and a new B-type texture components with basal poles rotated 20°-30° away from the normal direction (ND) toward the RD under the influence of variant selection of secondary α phase. However, the yield strength along the TD was still higher than that in the RD, indicating that the effect of texture on yield strength anisotropy was reduced. Finally, the electrical resistivity analysis of the titanium alloy sheet indicated that the electrical resistivity along the RD of the sheet was higher when the band structure was formed and the c-axis of the α phase was concentrated in the TD. However, the disappearance of the band structure and the increase in the volume fraction of the R-type texture will reduce the anisotropy of electrical resistivity.
Fig.1 Schematics of Ti-6Al-3Mo-2V-1Cr-2Sn-2Zr sampling positions (a) characterization specimen (ND—normal direction, RD—rolling direction, TD—transverse direction) (b) tensile specimen and electrical resistivity specimen along the RD and TD (c) tensile specimen dimension (unit: mm) (d) electrical resistivity specimen dimension (unit: mm)
Fig.2 SEM images of Ti-6Al-3Mo-2V-1Cr-2Sn-2Zr alloy sheet (αp—primary α phase) (a) RD-ND plane (b) RD-TD plane
Fig.3 Orientation imaging map of α phase in RD-ND plane (a), and pole figures of α phase (b) and β phase (c) in Ti-6Al-3Mo-2V-1Cr-2Sn-2Zr alloy sheet
Fig.4 Low (a-f) and high (a1-f1) magnified SEM images of air-cooled Ti-6Al-3Mo-2V-1Cr-2Sn-2Zr alloy sheet after annealing at 800oC (a, a1), 850oC (b, b1), 900oC (c, c1), 920oC (d, d1), 950oC (e, e1), and 1000oC (f, f1) for 1 h (αs—secondary α phase, αGB—grain boundary α phase, βt—β transformed phase)
Fig.5 Variations of volume fraction of αp phase and βt phase with annealing temperature (a) and variations of grain size of αp phase and αs phase with annealing temperature (b)
Fig.6 Pole figures of α phase obtained by XRD at 800oC (a), 850oC (b), 900oC (c), 920oC (d), 950oC (e), and 1000oC (f)
Fig.7 Pole figures of α phase obtained by EBSD at 800oC (a), 850oC (b), 900oC (c), 920oC (d), 950oC (e), and 1000oC (f)
Fig.8 EBSD analysis results of the 920oC annealed Ti-6Al-3Mo-2V-1Cr-2Sn-2Zr alloy sheet (a) pole figures of residual β phase (b) fore scatter diodes (FSD) map (c) orientation imaging map of α phase in RD-ND plane
Fig.9 Texture analysis results of the 1000oC annealed Ti-6Al-3Mo-2V-1Cr-2Sn-2Zr alloy sheet (a) misorientation angle distribution of α phase (b) (0002) pole figure of α phase obtained by XRD (c) (110) pole figure of residual β phase obtained by XRD (d) orientation imaging map of α lath I (e) EBSD measured (0001) pole figure corresponding to α lath I (f) EBSD measured (110) pole figure corresponding to residual β phase in Fig.9d (g) orientation imaging map of α lath II (h) EBSD measured (0001) pole figure corresponding to α lath II (i) EBSD measured (110) pole figure corresponding to residual β phase in Fig.9g
Fig.10 Tensile properties of Ti-6Al-3Mo-2V-1Cr-2Sn-2Zr alloy sheet at room temperature after annealing at different temperatures (a) yield strength (Rp0.2) (b) elongation (A)
Fig.11 Schmidt factor distributions along the RD (a) and TD (b) in Ti-6Al-3Mo-2V-1Cr-2Sn-2Zr alloy sheet with different slip systems of α phase
Fig.12 Inverse pole figures of RD and TD of α phase in Ti-6Al-3Mo-2V-1Cr-2Sn-2Zr alloy sheet after annealing at 800oC (a), 900oC (b), 920oC (c), 950oC (d), and 1000oC (e); and inverse pole figures along with isocurves of the maximum Schmidt factor for orientations in which basal slip (f) and prismatic slip (g)
Fig.13 Variations of electrical resistivity of RD and TD (a) and α texture volume fraction with annea-ling temperature (b) in Ti-6Al-3Mo-2V-1Cr-2Sn-2Zr alloy sheet
Fig.14 Effects of texture type on electron scattering of Ti-6Al-3Mo-2V-1Cr-2Sn-2Zr alloy sheet in different directions
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