Effect of Hydrostatic Pressure on Stress Corrosion Cracking of Cast and Forged Ti-6Al-4V Alloys

doi:10.11902/1005.4537.2025.313

Journal of Chinese Society for Corrosion and protection

2026, Vol. 46

Issue (4): 1031-1044 DOI: 10.11902/1005.4537.2025.313

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Effect of Hydrostatic Pressure on Stress Corrosion Cracking of Cast and Forged Ti-6Al-4V Alloys

XU Qiufa¹, GUO Yue¹, LIU Jun², YANG Dong³, CUI Yu³(

)

^1.Beijing Institute of Astronautical Systems Engineering, Beijing 050024, China
^2.State Key Laboratory of Digital Steel, Northeastern University, Shenyang 110819, China
^3.Shenyang National Laboratory for Materials Science, Institute of Metal Research, Chinese Academy of Sciences, Shenyang 110016, China

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XU Qiufa, GUO Yue, LIU Jun, YANG Dong, CUI Yu. Effect of Hydrostatic Pressure on Stress Corrosion Cracking of Cast and Forged Ti-6Al-4V Alloys. Journal of Chinese Society for Corrosion and protection, 2026, 46(4): 1031-1044.

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Abstract

The stress corrosion behavior of cast Ti-6Al-4V alloy, as an important engineering material of key structural components for deep-sea applications, in actual deep-sea conditions still remains unclear. In this study, the effect of hydrostatic pressure on the stress corrosion sensitivity and electrochemical behavior of the cast and forged Ti-6Al-4V alloys was comparatively studied by means of slow strain rate tensile testing and electrochemical testing techniques, scanning electron microscopy with electron backscatter diffraction (EBSD), etc. The results indicate that under the combined influence of high hydrostatic pressure and tensile stress, the transition of passivation films of both cast and forged Ti-alloys could occur from a dense structure gradually to a porous structure, thereby reducing their protectiveness. The coarse β-phase grain boundaries and defects in the cast Ti-alloy act as sites of weakness in the passivation film, which could significantly lower the compactness and corrosion resistance of the passivation film for the cast Ti-alloy. However, this effect was not observed in the forged Ti-alloy. The stress corrosion sensitivity of both types of Ti-6Al-4V alloys increases with hydrostatic pressure. In contrast, by the same hydrostatic pressure, the stress corrosion sensitivity of the cast Ti-6Al-4V alloy is higher than that of the forged Ti-6Al-4V alloy. Under high hydrostatic pressure, brittle fracture occurs for the cast Ti-6Al-4V alloy, and while ductile-brittle fracture for the forged Ti-6Al-4V alloy. Under high hydrostatic pressure, the applied tensile stress can induce dislocation motion, leading to stress concentration at the original β-phasegrain boundaries of the cast Ti-6Al-4V alloy. In fact, the existence of segregation defects can lead to the preferential damage of the passive film at those sites, and the cracks at the dendrites can initiate and propagate along the α/β phase interface in between the layers, and thus, the stress corrosion sensitivity is high. In contrast, the forged Ti-6Al-4V exhibits an equiaxed structure with a relatively dense passivation film, uniform deformation, and a strong ability of equiaxed crystals to resist crack propagation, thereby exhibiting relatively lower sensitivity to stress corrosion cracking.

Key words: hydrostatic pressure Ti-6Al-4V alloy stress corrosion casting

Received: 10 October 2025 32134.14.1005.4537.2025.313

ZTFLH:

TG174

Fund: Joint Fund of National Natural Science Foundation of China(U22A20111);Open Project of Key Laboratory of Marine Key Materials(2024K06)

Corresponding Authors: CUI Yu, E-mail: ycui@imr.ac.cn

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	XU Qiufa
	GUO Yue
	LIU Jun
	YANG Dong
	CUI Yu

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https://www.jcscp.org/EN/10.11902/1005.4537.2025.313 OR https://www.jcscp.org/EN/Y2026/V46/I4/1031

Fig.1 Metallographic structure of cast (a) and forged (b) Ti-6Al-4V alloy

Fig.2 Slow strain rate tensile of Ti-6Al-4V alloy: (a) stress-strain curves, (b) casting mechanical properties, (c) forging mechanical properties

Fig.3 Stress corrosion sensitivity of Ti-6Al-4V alloy: (a) I_SCC, (b) I_SSRT

Fig.4 Tensile fracture morphologies of cast Ti-6Al-4V alloy in different environments, macroscopic and local magnification: (a) in air, (b) 0.1 MPa, (c) 10 MPa, (d) 20 MPa

Fig.5 Tensile fracture morphologies of forged Ti-6Al-4V alloy in different environments, macroscopic and local magnifications: (a) in air, (b) 0.1 MPa, (c) 20 MPa

Fig.6 Fractal dimension of fracture dimples of Ti-6Al-4V alloy under different water pressures

Fig.7 Open circuit potential of Ti-6Al-4V alloy (U-bend specimen) under different hydrostatic pressures: (a) OCP, (b) local enlarged diagram of cast, (c) local enlarged diagram of forged

Fig.8 Potentiostatic polarization curves at 0.25 V of cast (a) and forged (b) Ti-6Al-4V alloy (U-shaped bending specimens) under different hydrostatic pressures

Fig.9 Nyquist (a1-e1) and Bode (a2-e2) of cast (a-c) and forged (d, e) Ti-6Al-4V alloy (U-bend specimens) under hydrostatic pressures of 0.1 MPa (a, d), 10 MPa (b) and 20 MPa (c, e), and fitting circuit (f)

Table 1 Fitting results of EIS of U-bend cast Ti-6Al-4V alloy samples under different hydrostatic pressures

Table 2 Fitting results of EIS of U-bend forged Ti-6Al-4V alloy samples under different hydrostatic pressures

Fig.10 Potentiodynamic polarization curves of Ti-6Al-4V alloy (U-bend specimen) under different hydrostatic pressures

Fig.11 Results of EBSD inverse pole figure of Ti-6Al-4V alloy slow tensile fracture under 20 MPa hydrostatic pressure: (a) IPF diagram of tensile direction of the cast sample, (b) IPF of the forged sample, (c) reverse pole figure of cast sample, (d) reverse pole figure of forged sample

Fig.12 EBSD results of Ti-6Al-4V alloys slow tensile fracture under 20 MPa hydrostatic pressure: (a) kernel average misorientation (KAM) and (b) grain boundary (GB)

Fig.13 EIS analysis of Ti-6Al-4V alloy (U-bend specimens) under different hydrostatic pressures: (a) R_f change curves, (b) R_f ratio results under different hydrostatic pressures, (c) the curves of 1/C_effchanging with time

Fig.14 A schematic diagram of stress corrosion cracking mechanism of cast Ti-6Al-4V alloy under 20 MPa hydrostatic pressure

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