EBSD‐assisted fractography of sub‐surface fatigue crack initiation mechanism in the ultrasonic‐shot‐peened βeta‐type titanium alloy

Uematsu, Yoshihiko; Kakiuchi, Toshifumi; Hattori, Kanehisa

doi:10.1111/ffe.12812

Cited by 17 publications

(17 citation statements)

References 19 publications

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“…The increase in hardness by shot peening has been previously explained through two hardening mechanisms which occur during shot peening: (1) grain refinement and twinning [ 7 , 29 , 81 ] and (2) plastic deformation [ 7 , 29 , 66 , 81 , 82 ]. The influences of both hardening mechanisms may vary depending on the microstructure and the composition of α and β phases in Ti6Al4V alloy [ 20 ].…”

Section: Resultsmentioning

confidence: 99%

“…Numerous studies have investigated the fatigue life enhancement of Ti alloys (specifically Ti6Al4V) by performing shot peening with various parameters [ 24 , 43 , 65 , 66 , 67 , 68 , 69 , 70 ]. However, only a few studies have investigated the effects of shot peening and its parameters on the surface and subsurface properties of materials such as surface roughness, morphology, topography, and hardness in relation to their tribological behavior [ 34 , 44 , 71 ].…”

Section: Introductionmentioning

confidence: 99%

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Surface, Subsurface and Tribological Properties of Ti6Al4V Alloy Shot Peened under Different Parameters

et al. 2020

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Ti6Al4V alloy was shot peened by using stainless-steel shots with different sizes (0.09–0.14 mm (S10) and 0.7–1.0 mm (S60)) for two durations (5 and 15 min) using a custom-designed peening system. The shot size was the main parameter modifying the roughness (0.74 µm for S10 vs. 2.27 µm for S60), whereas a higher peening time slightly increased roughness. Hardness improved up to approximately 35% by peening with large shots, while peening time was insignificant in hardness improvement. However, longer peening duration with large shots led to an unwanted formation of micro-cracks and delamination on the peened surfaces. After dry sliding wear tests, the mass loss of peened samples (S60 for 15 min) was 25% higher than that of un-peened samples, while the coefficient of friction decreased by 12%. Plastically deformed regions and micro-scratches were observed on the worn surfaces, which corresponds to mostly adhesive and abrasive wear mechanisms. The present study sheds light on how surface, subsurface and tribological properties of Ti6Al4V vary with shot peening and peening parameters, which paves the way for the understanding of the mechanical, surface, and tribological behavior of shot peened Ti6Al4V used in both aerospace and biomedical applications.

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Section: Resultsmentioning

confidence: 99%

Section: Introductionmentioning

confidence: 99%

Surface, Subsurface and Tribological Properties of Ti6Al4V Alloy Shot Peened under Different Parameters

et al. 2020

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“…A fatigue crack was initiated from the matrix, and no inclusion or void was observed at the fracture origin in each specimen regardless of the stress ratios. In addition, radial patterns, which were initiated from the crack initiation site, were confirmed on the fracture surfaces [11,15,21,22].…”

Section: Fracture Surface Characteristicsmentioning

confidence: 78%

Initiation and Propagation Processes of Internal Fatigue Cracks in β Titanium Alloy Based on Fractographic Analysis

et al. 2020

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Uniaxial fatigue tests were conducted for a β titanium alloy Ti-22V-4Al up to a very high cycle fatigue (VHCF) regime. The initiation and propagation processes of the internal fatigue cracks were investigated using 3D fractographic analysis. Multiple facets were observed at the crack initiation site. Three facet initiation models were proposed based on the surface appearances and the 3D facet bonding patterns of the multiple facets, and the major facet was determined to be the true crack initiation site. Using the size of the major facet, a Tanaka–Akiniwa model, which can determine the material constants for the Paris law using only conventional fatigue tests, was applied to reveal the propagation process of the internal cracks. A reverse fatigue life prediction was also conducted to evaluate the accuracy of the material constants obtained using the Tanaka–Akiniwa model. When the facet initiation models were applied, the predictions showed less deviation and better agreement than when the facet initiation process was not considered. The findings of this study indicate that the formation of multiple facets in β titanium alloys is sequential rather than simultaneous.

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“…In general, sub-surface crack initiation is typically seen in HCF fracture of high strength steels 24,25) or surface treated alloys, such as DLC-coated magnesium alloy 26) or ultrasonic shot-peened ¢-type Ti alloy. 27) But sub-surface crack initiation was hardly reported Table 1 Mechanical properties of material. Figs.…”

Section: Microstructures and Mechanical Propertiesmentioning

confidence: 99%

Fatigue Behavior of Multi-Directionally Forged Commercial Purity Grade 2 Ti Plate in Laboratory Air and Ringer’s Solution

Ilhamdi

Kakiuchi²,

Miura

et al. 2018

Mater. Trans.

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Ultrafine-grained pure titanium (Ti) plates with the thickness of 1 mm were fabricated by a combined process of multi-directional forging (MDFing) and cold rolling (here after referred as MDFed pure Ti for simplicity) aiming at the dental implant application. The plates exhibited higher tensile strength than the conventional cold-rolled pure Ti plates due to the ultrafine-grained structure with an average size of 200 nm. The axial fatigue tests were conducted in laboratory air and in Ringer's solution to investigate long-term durability as dental implants. The fatigue strengths of the MDFed pure Ti plates in laboratory air were higher than those of the cold-rolled pure Ti plates as well as the tensile properties. In the high cycle fatigue (HCF) regime, sub-surface crack initiation with fish-eye fracture surface was observed in the MDFed pure Ti plates, while surface crack initiation was dominant in the cold-rolled pure Ti plates. Sub-surface crack generally initiated at the mid-thickness of the thin plates. Inclusions were not recognized at the crack initiation sites, while microstructural analyses revealed that some coarse grains with the size of a few µm distributed around the crack initiation sites. Consequently, the sub-surface crack initiation mechanism was attributed to the inhomogeneity of the microstructure near the mid-thickness of the plates. The corrosion fatigue strengths in Ringer's solution were comparable to those in laboratory air, where sub-surface crack initiation occurred in the HCF regime even in corrosive environment. That indicates the high corrosion resistance of the MDFed pure Ti plates.

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EBSD‐assisted fractography of sub‐surface fatigue crack initiation mechanism in the ultrasonic‐shot‐peened βeta‐type titanium alloy

Cited by 17 publications

References 19 publications

Surface, Subsurface and Tribological Properties of Ti6Al4V Alloy Shot Peened under Different Parameters

Surface, Subsurface and Tribological Properties of Ti6Al4V Alloy Shot Peened under Different Parameters

Initiation and Propagation Processes of Internal Fatigue Cracks in β Titanium Alloy Based on Fractographic Analysis

Fatigue Behavior of Multi-Directionally Forged Commercial Purity Grade 2 Ti Plate in Laboratory Air and Ringer’s Solution

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