The Cracking of Ti-6Al-4V Alloys Under Sustained Load in Ambient Air

Yoder, G. R.; Griffis, C. A.; Crooker, T. W.

doi:10.1115/1.3443241

Cited by 14 publications

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“…This mechanism is applicable to the FCG at high mean stress levels in these alloy system. Although this phenomenon is also commonly observed in conventional titanium alloys as well [39,40], it appears that the intensity of it is much higher in the alloys: Ti-8.6A1, Ti-24A1-1 INb and Ti-33.5Al-2.5Mn. Because the average static "K" (K mean ) at high R is higher, static crack extension can be expected to occur, in addition to the cyclic crack extension produced by the cyclic stress intensity range (AK).…”

Section: Microstructurementioning

confidence: 64%

Fatigue of Bet Titanium Alloys

Ravichandran¹

2000

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0«DTXC QUÄLTET IK'SKüuxiiii) 3 REPORT DOCUMENTATION PAGE AFRL-SR-BL-TR-OO- Public reporting burden for this collection of information is estimated to average 1 hour per response, including the time for reviewing instruc the collection of information. Send comments regarding this burden estimate or any other aspect of this collection of information, inclu ABSTRACT (Maximum 200 words)A comprehensive investigation of the nature of fatigue in beta titanium alloys, especially in Ti-10V-3Fe-3Al alloy, emphasizing the crack initiation and crack growth aspects in controlled microstructural conditions, was performed. A detailed survey of literature of past work in this area, was also conducted. It has been found that the fatigue limit in this alloy is independent of the size, shape and volume fraction of the primary alpha particles. The matrix condition, as determined by the aging treatment had a strong influence on the fatigue behavior. It has been found that fatigue resistance could be improved only by controlling the aging treatment, that resulted in changes in the matrix microstructure. A mysterious fatigue behavior, exhibiting dual stress versus number of cycles to failure was also found in one microstructural condition. Aging treatments that resulted in omega phase precipitation, decreased the fatigue strength. In terms of fatigue crack growth response, omega phase increased the resistance to crack growth. Additionally, a strong sensitivity of fatigue crack growth to mean stress was also found with the omega precipitation. An evaluation of fatigue behavior of various titanium alloys was also made. It was concluded that microstructural refinement led to the minimal mean stress sensitivity in conventionally aged beta alloys, in comparison to other titanium alloys. The results are discussed in the light of microstructure, electron microscopy, fractography and quantitatitve determination of chemistry by energy-dispersive chemical analysis. SUBJECT TERMS SUMMARYA comprehensive investigation of the nature of fatigue in beta titanium alloys, especially in Ti-10V-3Fe-3Al alloy, emphasizing the crack initiation and crack growth aspects in controlled microstructural conditions, was performed. A detailed survey of literature of past work in this area, was also conducted. It has been found that the fatigue limit in this alloy is independent of the size, shape and volume fraction of the primary alpha particles. The matrix condition, as determined by the aging treatment had a strong influence on the fatigue behavior. It has been found that fatigue resistance could be improved only by controlling the aging treatment, that resulted in changes in the matrix microstructure. A mysterious fatigue behavior, exhibiting dual stress versus number of cycles to failure was also found in one microstructural condition.Aging treatments that resulted in omega phase precipitation, decreased the fatigue strength. In terms of fatigue crack growth response, omega phase increased the resistance to crack growth.Additionally, a strong sensitivity of...

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Section: Microstructurementioning

confidence: 64%

Fatigue of Bet Titanium Alloys

Ravichandran¹

2000

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“…Static load cracking in titanium alloys at temperatures below the secondary creep regime (i.e., at test temperature/melting-point ratios, T/T , of less than 0.4) is not completely understood[32][33][34][35]. A successful theory must rationalize several observations: that the resistance to fracture under static loading is reduced by electron beam welding, that different mechanisms are involved in base and weld metal specimens, and that cracking rates at low temperatures (195 K) may be more severe than at room temperature.At the 50 ppm level of the present alloy, interstitial hydrogen may facilitate cracking by diffusing to and concentrating at regions of high stress[35][36][37][38].…”

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confidence: 99%

Low temperature fracture behavior of a Ti-6Al-4V alloy and its electron beam welds

Tobler¹

1976

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The effects of electron beam (EB) welding on the fracture behavior of a recrystallization annealed, extra-low-interstitial Ti-6A1-4V alloy have been investigated at temperatures in the ambient-to-cryogenic range. Plane strain fracture toughness (K T) and subcritical crack growth parameters were measured Ic using compact specimens 10 to 25.4 mm thick. These parameters can be used to predict the safe operating lifetimes of cryogenic pressure vessels and other welded Ti-6A1-4V structures. Although EB welding transforms the base metal microstructure extensively, its effects on the material's fatigue crack propagation resistance at intermediate stress intensity factors are negligible. The growth rates, da/dN, of fatigue cracks sited in the fusion and heat-affected zones of weldments were temperature insensitive and nearly equivalent to rates for the base metal. However, welding introduces a zone of low fracture toughness at the heat-affected-zone/fusionzone boundary. The K value for this boundary zone at liquid 3/2 nitrogen temperature (76 K) was 45 MN/m , 16% lower than the base metal. The base metal fracture toughness increases between 4 and 295 K, with an abrupt transition to higher K values occurring at temperatures between 76 and 125 K. Static load cracking, temperature effects, and specimen orientation effects on the fracture behavior of this titanium alloy are central topics of discussion.

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Influence of vanadium on hydrogen diffusion and phase constitution in Ti–H

Korn

Teitel

1977

Phys. Stat. Sol. (a)

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The nuclear magnetic resonance method is used to investigate the influence of small amounts of vanadium on the phase constitution and hydrogen diffusion in Ti‐H. The temperature dependence of the proton spin‐lattice relaxation time is obtained at 27 MHz for samples representative of the α, β and γ phases of the system. The influence of V on the Ti‐H phase diagram is presented. The probable location of hydrogen in the β phase is found to be the octahedral Oz sites of the b.c.c. lattice. It is determined that the hydrogen diffusion activation energy Ea in the β phase of Ti‐H containing about 4% V is (2.3 ± 0.1) kcal/mole which is about 1/3 of that obtained for the vanadium free case. This amount of vanadium has very little effect on the activation energy in the α phase where it is found that Ea = (11.5 ± 0.8) kcal/mole. It is also found that vanadium decreases the hydrogen diffusion activation energy in the γ phase and causes a non‐linearity in the Arrhenius plot. The lower temperature activation energies are found to be 11.2, 9.7, and 9.0 kcal/mole for TiH1.70 + 1.03% V, TiH1.74 + 2.59% V, and TiH1.63 + 4.36% V, respectively, where the vanadium percentage is the metal percentage prior to the introduction of hydrogen. The consequences of these effects on the problem of hydrogen embrittlement is discussed.

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The Cracking of Ti-6Al-4V Alloys Under Sustained Load in Ambient Air

Cited by 14 publications

References 0 publications

Fatigue of Bet Titanium Alloys

Fatigue of Bet Titanium Alloys

Low temperature fracture behavior of a Ti-6Al-4V alloy and its electron beam welds

Influence of vanadium on hydrogen diffusion and phase constitution in Ti–H

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