The influence of porosity on the fatigue crack growth behavior of Ti-6Al-4V laser welds

The effect of porosity––a common welding defect––on the fatigue crack growth rate (FCGR) in Ti–6Al–4V laser welds was investigated. The experimental results reveal that porosity was present in partial penetration welds over a narrow fusion zone (FZ) with martensite structure. The FCGR of the FZ was...

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Bibliographic Details
Published in:Journal of materials science 2006-11, Vol.41 (22), p.7498-7505
Main Authors: TSAY, L. W, SHAN, Y. P, CHAO, Y.-H, SHU, W. Y
Format: Article
Language:English
Subjects:
Applied sciences
Crack propagation
Crack tips
Cross-disciplinary physics: materials science
rheology
Exact sciences and technology
Fatigue
Fatigue failure
Fracture mechanics
Fracture surfaces
Joining, thermal cutting: metallurgical aspects
Laser beam welding
Martensite
Materials science
Mechanical properties and methods of testing. Rheology. Fracture mechanics. Tribology
Metals. Metallurgy
Morphology
Other topics in materials science
Physics
Planes
Plates (structural members)
Porosity
Stress ratio
Titanium base alloys
Weld metal
Welded joints
Welding
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Summary:The effect of porosity––a common welding defect––on the fatigue crack growth rate (FCGR) in Ti–6Al–4V laser welds was investigated. The experimental results reveal that porosity was present in partial penetration welds over a narrow fusion zone (FZ) with martensite structure. The FCGR of the FZ was lower than that of the base plate. The fracture surface morphology of weld metal was much rougher as compared to that of the base plate. Randomly oriented martensite in the FZ led to local cleavage fracture along a preferred plane, thus, altering the crack growth direction significantly out of the primary crack plane. The zigzag crack path in the FZ resulted in a reduced FCGR at a given ΔK compared to the base plate. Besides, the porous weld showed a serration on the crack growth curve, and behaved the similar crack growth characteristics as the defect free one. SEM fractography revealed that the deflection of crack path around porosity together with local notch blunting as the crack tip pierced into porosity, balanced the increased FCGR for the occurrence of instant crack advance as the crack front reached the porosity at a low stress ratio. In contrast, the serration and drop in FCGR occurred sparingly at a high stress ratio as the crack front met the porosity.
ISSN:0022-2461
1573-4803
DOI:10.1007/s10853-006-0833-x