Author: James R. WilcoxPublisher:
ISBN:
Category :
Languages : en
Pages : 130
Book Description
Hydrogen-assisted Fatigue Crack Propagation in a Beta Titanium Alloy
Author: James R. WilcoxThe Effect of O2, H2O, and N2 on the Fatigue Crack Growth Behavior of an Alpha + Beta Titanium Alloy at 24 C and 177 C
Author: Stephen W. SmithAtmospheric Influence on Fatigue Crack Propagation in Titanium Alloys at Elevated Temperature
Author: S. LesterlinPublisher:
ISBN:
Category : Environment
Languages : en
Pages : 23
Book Description
The fatigue crack propagation behavior of a Ti-6Al-4V alloy has been investigated at room temperature and at 300°C. Tests were run in air, high vacuum, and some other environments with controlled partial pressure of water vapor and oxygen. The enhancement of the fatigue crack growth rates observed in air in comparison to high vacuum, considered as an inert environment, is clearly attributed to the presence of water vapor. Tests in a controlled environment demonstrate that very low partial pressure can accelerate crack propagation. On the basis of previous studies on Al alloys and steels, two controlling mechanisms are considered and discussed, namely, a propagation-assisted water vapor adsorption and a hydrogen-assisted propagation.
Fractographic Analysis of Hydrogen-Assisted Cracking in Alpha-Beta Titanium Alloys
Author: RA. BaylesPublisher:
ISBN:
Category : Composite materials
Languages : en
Pages : 24
Book Description
The role of hydrogen in the subcritical crack growth of titanium alloys is a subject of intense interest to those who use these alloys for structural applications. The most widely accepted theories are based on the absorption of hydrogen (in the case of environmental hydrogen-assisted cracking), its diffusion to regions of high tensile stress, and the initiation of microcracks at hydrides precipitated in such regions. One of the difficulties with such a mechanism is the paucity of observations of titanium hydrides on fracture surfaces, such as those caused by stress corrosion cracking or inert-environment sustained load cracking caused by residual hydrogen impurity. Another difficulty has been the identity in microstructural crack paths between stress corrosion cracking in hydrogen-containing (saltwater, etc.) and hydrogen-free (carbon tetrachloride) environments.
Effect of Hydrogen on Flow and Fracture in a Β-titanium Alloy
Author: Kumar V. JatavallabhulaPublisher:
ISBN:
Category :
Languages : en
Pages : 388
Book Description
The Effect of O2, H2o, and N2 on the Fatigue Crack Growth Behavior of an Alpha + Beta Titanium Alloy at 24 C and 177 C
Author: National Aeronautics and Space Adm NasaPublisher: Independently Published
ISBN: 9781723767173
Category : Science
Languages : en
Pages : 34
Book Description
To study the effects of atmospheric species on the fatigue crack growth behavior of an a+B titanium alloy (Ti 6-2-2-2-2) at room temperature and 177 C, fatigue tests were performed in laboratory air, ultrahigh vacuum, and high purity water vapor, oxygen, nitrogen and helium at various partial pressures. Accelerated fatigue crack growth rates in laboratory air compared to ultrahigh vacuum are linked to the damaging effects of both water vapor and oxygen. Observations of the fatigue crack growth behavior in ultrahigh purity environments, along with surface film analysis using X-ray photoelectron spectroscopy (XPS), suggest that multiple crack-tip processes govern the damaging effects of air. Three possible mechanisms are proposed: 1) at low pressure (less than 10(exp -1) Pa), accelerated da/dN is likely due to monolayer adsorption on crack-tip surfaces presumably resulting in decreased bond strengths at the fatigue crack tip, 2) for pressures greater than 10(exp -1) Pa, accelerated da/dN in oxygen may result from oxidation at the crack tip limiting reversible slip, and 3) in water vapor, absorption of atomic hydrogen at the reactive crack tip resulting in process zone embrittlement.Smith, Stephen W. and Piascik, Robert S.Langley Research CenterFATIGUE TESTS; FATIGUE (MATERIALS); CRACK PROPAGATION; TITANIUM ALLOYS; EMBRITTLEMENT; ATMOSPHERIC COMPOSITION; X RAY SPECTROSCOPY; WATER VAPOR; ULTRAHIGH VACUUM; PHOTOELECTRON SPECTROSCOPY
Maco/Micro Studies of Hydrogen Embrittlement Mechanisms in Titanium and Aluminum Alloys
Author: W. W. GerberichPublisher:
ISBN:
Category : Alloys
Languages : en
Pages : 25
Book Description
Systematic studies of environmental effects on fracture in two alpha/beta titanium alloys, one beta titanium alloy and 7475 aluminum alloys have been accomplished. Ti-6Al-6V-2Sn has been tested for its hydrogen-induced cracking behavior under sustained loads. The influence of frequency and microstructure on fatigue crack growth have also been studied. Fatigue crack growth in Ti-5A1-4Mo, as a function of hydrogen content, temperature and Widmanstatten colony size, was then studied. Mechanical data have been obtained along with TEM and SEM characterizations. Modelling for fatigue thresholds has been attempted to explain dislocation, microstructure and hydrogen effects. Ti-30 Mo has been studied for effects of hydrogen on dislocation dynamics, cleavage fracture stress and fatigue crack propagation. Fractography (SEM) has been used to characterize the fracturing processes and modeling attempted to explain the hydrogen effects. Hydrogen effects in aluminum alloys are not as obvious as those in titanium alloys. Both cathodic and gas-phase charging did not significantly increase the hydrogen content of this material. Mechanical properties did not seem to change decisively after hydrogen charging. But the lack of a macroscopic effect does not preclude a hydrogen mechanism in environmentally assisted events. (Author).
A Film-rupture Model of Hydrogen-induced, Slow Crack Growth in Alpha-beta Titanium
Author: Environmentally assisted cracking of high strength beta titanium alloys
Author: Publisher:
ISBN:
Category :
Languages : en
Pages : 59
Book Description
The objective of this research is to define the conditions under which high strength beta-titanium alloys are resistant to environmentally assisted cracking (EAC) in marine environments. Our goals are to: (1) characterize environment enhanced subcritical crack propagation behavior for metallurgical, chemical and mechanical loading conditions that could destabilize crack tip passive films to promote local dissolution and hydrogen uptake, (2) test the hydrogen embrittlement mechanism for EAC, and (3) develop a mechanism- based predictive model of EAC by integrating occluded crack chemistry, surface repassivation, hydrogen uptake and segregation at trap sites, and crack tip process zone micromechanics and damage. The behavior of two peak aged beta alloys, Beta 21S (Ti-15Mo-2.7Nb-3AI by wt% and sigma sub ys = 1380 MPa) and Ti- 15-3 (Ti-15V-3Cr-3AI-3Sn; sigma sub ys = 1315 MPa) plate, was emphasized during this reporting period. Three papers were published; each is summarized as follows. Titanium alloys, Hydrogen embrittlement, Mechanical properties, Intergranular cracking, Transgranular cracking, Microstructure, Alpha precipitates, Beta phase, Hydrides, Passive film, Beta titanium alloys, Fracture threshold.
Author: Jeffrey A. Carlson