Mechanical properties of electron beam welded dissimilar joints of TC17 and Ti60 alloys

doi:10.1016/j.jmst.2018.02.014

Abstract

Abstract:

Microstructure, hardness, tensile and high cycle fatigue (HCF) properties of the welded dissimilar joints of Ti60 and TC17 titanium alloys had been investigated in this study. A significant microstructural change was observed to occur after welding, with rod-like α and β phases in the fusion zone (FZ), equiaxed α phases, fine α laths and β phases in the heat-affected zone (HAZ) of TC17 side and acicular martensite α' phases+“ghost” α phases in the HAZ of Ti60 side. The microhardness across the joints exhibited an inhomogeneous distribution with the highest hardness of ～404 HV in FZ and the lowest hardness of ～304 HV in base material (BM) of Ti60. All the joints tested in tension fractured at BM of Ti60 side. Fatigue limits of the joints at 10⁷ cycles were 425 MPa at room temperature and 380 MPa at 400 °C, respectively. Welding micropores were found to be the main source of fatigue crack initiation.

Key words: Titanium alloy, Electron beam welding, Dissimilar joints, Mechanical properties

Chao Cheng, Bingbing Yu, Zhiyong Chen, Jianrong Liu, . Mechanical properties of electron beam welded dissimilar joints of TC17 and Ti60 alloys[J]. J. Mater. Sci. Technol., 2018, 34(10): 1859-1866.

Figures/Tables 12

Fig. 1. Microstructure of BMs of (a) Ti60 alloy and (b) TC17 titanium alloy.

Fig. 2. Geometry and dimensions of welded joint and the position of the FZ: (a) tensile specimen (mm); (b) fatigue specimen (mm).

Fig. 3. Macrograph and microstructure of the dissimilar joints between Ti60 and TC17 alloys: (a) macrostructure of weldment; (b) center of FZ; (c) inter HAZ and (d) outer HAZ of TC17 side; (e) HAZ of Ti60 side.

Fig. 4. TEM microstructure of FZ.

Fig. 5. XRD pattern of FZ.

Fig. 6. Microhardness across the dissimilar joints.

Table 1 Tensile properties of the BMs and TC17/Ti60 dissimilar joints.

Temperature (°C)	Material	R_p0.2 (MPa)	R_m (MPa)	A (%)	Failure location
RT	Ti60	962	1062	10.5	-
	TC17	1145	1182	12.0	-
	joint	1012	1077	7.0	Ti60
400	Ti60	623	770	21.7	-
	TC17	832	950	10.3	-
	joint	680	793	8.0	Ti60

Fig. 7. S-N curves of TC17/Ti60 dissimilar joints at (a) RT and (b) 400 °C.

Fig. 8. Goodman diagrams of the TC17/Ti60 dissimilar joints at (a) RT and (b) 400 °C.

Fig. 9. SEM of the fracture surface of the dissimilar joints fatigued at room temperature: (a) full view of fracture for micropores located in FZ; (b) magnification images of final fast fracture region of (a); (c) full view of fracture for micropores located in fusion line of TC17 alloy; (d) magnification images of final fast fracture region of (c).

Fig. 10. Macroscope of the fracture surface of the dissimilar joints fatigued at 400 °C for different stress amplitudes: (a) 500 MPa; (b) 385 MPa.

Fig. 11. High magnification SEM images of fracture surfaces at 400 °C: (a) crack initiation site; (b) propagation area and (c) final fast fracture region for 500 MPa; (d) crack initiation site; (e) propagation area and (f) final fast fracture region for 385 MPa.

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