Unveiling the Residual Stresses, Local Micromechanical Properties and Crystallographic Texture in a Ti-6Al-4V Weld Joint

doi:10.1007/s40195-020-01183-0

Abstract

Abstract:

In this work, the micromechanical properties, crystallographic texture, welding residual stresses and their evolution after plastic strain were investigated in a Ti-6Al-4 V alloy tungsten inert gas weld joint. It was found that the welding process affected the Young modulus and microhardness values in both α and β phases in the different regions of the weld joint. The highest microhardness and Young modulus values of α phase were recorded in the heat-affected zone, whereas the highest values of these characteristics for the β phase were found in the fusion zone (FZ). The change in the micromechanical properties was accompanied by a change in the crystallographic texture components of the dominant α phase from (0001) < 10-10 > and (11-20) < 10-10 > components in the base material to (10-10) < 11-20 > and (11-20) < 3-302 > components in the FZ. The introduction of tensile testing resulted in a continuous stress relaxation and improved the weld joint performances.

Key words: Ti-6Al-4 V, Tungsten inert gas (TIG) weld, Residual stress, Local mechanical properties, Crystallographic texture

B. Mehdi, R. Badji, V. Ji, B. Alili, D. Bradai, W. Bedjaoui, F. Deschaux-Beaume, F. Brisset. Unveiling the Residual Stresses, Local Micromechanical Properties and Crystallographic Texture in a Ti-6Al-4V Weld Joint[J]. Acta Metallurgica Sinica (English Letters), 2021, 34(7): 997-1006.

Figures/Tables 17

Table 1 Chemical composition of the studied Ti-6Al-4 V alloy

Element	Al	Ti	V	Fe
(wt%)	5.65	90.25	3.85	0.25
(at.%)	14.84	81.82	3.08	0.26

Fig. 1 a Vacuum chamber used for the Ti-6Al-4 V TIG welding, b specimen of the welded sheets

Table 2 Used welding parameters

Element	Al	Ti	V	Fe
(wt%)	5.65	90.25	3.85	0.25
(at.%)	14.84	81.82	3.08	0.26

Table 3 Residual stress measurement parameters

Parameters	Values
Ψ angles: 28° (by step of 5°)	- 70 to + 70°
Atomic plane for deformation $\varepsilon_{\phi \psi }$ measurements	(2 1-3 3)
Diffraction angle for the associate peak	2θ = 142°
Elastic constants of the studied material	Young modulus: E = 120 GPa Poisson coefficient: ν = 0.33
Anisotropic factor A_RX	1
Stress analysis precision	± 10 MPa

Fig. 2 X-ray patterns of the different zones of Ti-6Al-4 V TIG weld

Fig. 3 Evolution of the microhardness HV0.3in the different regions of Ti-6Al-4 V TIG weld

Fig. 4 Optical image of indentations obtained in the FZ

Fig. 5 P-h curves of α phase in the different weld zones Ti-6Al-4 V TIG weld

Fig. 6 Evolution of: a Young’s modulus and b microhardness of the α and β phases in the different weld zones

Table 4 Micromechanical properties in the different regions of the investigated Ti-6Al-4 V weld joint obtained from nanoindentation measurements

Weld zones	Young’s modulus, E_β (GPa)	Microhardness, H_β (MPa)	Young’s modulus, E_α (GPa)	Microhardness, H_α (MPa)
BM	100 ± 0.9	3500 ± 110	125 ± 0.9	4840 ± 110
HAZ	104 ± 1.2	3000 ± 90	140 ± 1.2	5080 ± 90
FZ	108 ± 1.6	3600 ± 120	135 ± 1.6	4952 ± 120

Fig. 7 Longitudinal (σL) and transversal (σT) welding residual stress in the different regions of the Ti-6Al-4 V TIG weld

Fig. 8 a Tensile curves obtained during interrupted tensile tests, b mean residual stress evolution in the different weld zones after interrupted tensile tests

Fig. 9 a Macrographs of the welded sheet illustrated in different regions, b inverse pole figure (IPF) maps obtained for the BM, c IPF maps obtained for the BM/HAZ, d IPF maps obtained for the HAZ, e IPF maps obtained for the FZ

Fig. 10 Recalculated (0001) and (10-10) pole figures obtained from EBSD measurements in BM, BM/HAZ, HAZ and FZ zones

Fig. 11 Identified hexagonal texture components observed in the present study

Fig. 12 Grain boundary character distribution in the BM, BM/HAZ, HAZ and FZ zones

Fig. 13 Histogram of misorientation angle distribution in the BM, BM/HAZ, HAZ and FZ zones

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