The Experts below are selected from a list of 645 Experts worldwide ranked by ideXlab platform
Digby D Macdonald - One of the best experts on this subject based on the ideXlab platform.
-
prediction of corrosion fatigue crack growth rate in alloys part ii effect of electrochemical potential nacl concentration and temperature on crack propagation in aa2024 t351
Corrosion Science, 2019Co-Authors: Danyil Kovalov, Balazs Fekete, George R Engelhardt, Digby D MacdonaldAbstract:Abstract We report here on the prediction of corrosion fatigue crack growth rate (CFCGR) for Aluminum Alloy 2024-T351 in aqueous environments under cyclical sinusoidal loading. Using the General Corrosion Fatigue Model (GCFM) described in Part I, the CFCGR was calculated as a function of environmental variables, including the electrochemical potential, NaCl concentration, loading frequency, stress intensity factor range, and temperature, in addition to the contribution from mechanical fatigue. Based on the influence of the environment, the changes in the potential drop down the crack enclave and the corrosion current density in a 1:1 electrolyte were also calculated from which the CFCGR was estimated. Corrosion fatigue crack growth in this alloy is readily understood in terms of the competition between environmental factors as described by the Differential Aeration hypothesis and the hydromechanics (advection) of the system resulting from the cyclical opening and closing of the crack.
-
prediction of corrosion fatigue crack growth rate in alloys part i general corrosion fatigue model for aero space aluminum alloys
Corrosion Science, 2018Co-Authors: Danyil Kovalov, Balazs Fekete, George R Engelhardt, Digby D MacdonaldAbstract:Abstract In this work, a General Corrosion Fatigue Model (GCFM) was developed for predicting corrosion fatigue crack growth rate (CFCGR) in metals under cyclical loading. The GCFM is based on an equation for the potential drop from the external surface to the crack tip of metals as derived from the principle of Differential Aeration. Development of the GCFM involves consideration of cyclic loading on the CFCGR and of advection between the in-crack and external environment. We demonstrate the influence of corrosion environment and cyclic loading on the crack growth rate in Al-Li alloys in a 1:1 electrolyte (0.6 M NaCl).
-
The mechanism of stress corrosion cracking in sensitized austenitic stainless steels in nuclear power reactor heat transport circuits
2014 IEEE Conference on Technologies for Sustainability (SusTech), 2014Co-Authors: Digby D Macdonald, Jiangbo ShiAbstract:Extensive work over almost the past hundred years has suggested that the stress corrosion cracking of metals and alloys in aqueous environments is primarily an electrochemical phenomenon falling within the realm of the Differential Aeration hypothesis (DAH). An important feature of the DAH is that the local anode and the local cathode are spatially separated, with the former existing within the crack enclave (on the crack flanks and at the crack tip) and the latter existing on the bold, external surfaces. Because of the need to compensate the positive charge being deposited into the crack cavity from metal dissolution, anions (e.g, Cl−) are transported into the crack, a process that is manifest as a positive current flowing from the crack to the external surfaces, where it is consumed by hydrogen ion, water, and/or oxygen reduction. Thus, strong electrochemical coupling exists between the crack internal and external surfaces and this coupling has been observed in stress corrosion cracking in a variety of systems, including IGSCC in sensitized Type 304 SS in simulated BWR coolant environments at 288°C. Examination of this “coupling current” shows that it contains “structured” noise superimposed upon a mean. In the case of the sensitized stainless steel in the high temperature aqueous environment, the mean current is found to be linearly related to the crack propagation rate. Furthermore, the noise in the current is found to yield a wealth of information on the fracture events that occur at the crack tip, including their frequency, temporal relationship with other events, and size. This information has provided a clearer view of the fracture mechanisms.
-
stress corrosion cracking of sensitized type 304 stainless steel in thiosulfate solution i fate of the coupling current
Corrosion Science, 2003Co-Authors: Monika Gomezduran, Digby D MacdonaldAbstract:This work explores the fate of the coupling current generated during stress corrosion cracking of sensitized Type 304 stainless steel (304SS) in thiosulfate solution at ambient temperature. The coupling current, which is generated inside the crack, may be consumed (as required by charge conservation) by cathodic reactions at two different locations: inside the crack (e.g., on the crack flanks) and on the external surfaces. Experiments were conducted using sensitized Type 304SS compact tension specimens C(T) modified to provide external surfaces isolated from the specimen itself, so that the coupling current flowing between the crack and the external cathode could be directly monitored using a zero-resistance ammeter. The results demonstrate that significant coupling current flows from the crack to the external surface, consistent with the Differential Aeration hypothesis for localized corrosion. Coupling current data from specimens heat treated at 650 °C for 4, 14, and 24 h show that 4 h of sensitizing heat treatment apparently does not induce significant sensitization, while 14 h of heat treatment is sufficient to produce a fully sensitized microstructure, equivalent to that obtained after 24 h of heating. Finally, the crack was determined to grow via discrete microfracture events at the crack front with a dimension of the order of the grain size. The observations are more consistent with crack growth being due to a hydrogen induced fracture mechanism rather than slip/dissolution.
Jeremy L Gilbert - One of the best experts on this subject based on the ideXlab platform.
-
in vivo severe corrosion and hydrogen embrittlement of retrieved modular body titanium alloy hip implants
Journal of Biomedical Materials Research Part B, 2009Co-Authors: Danieli C Rodrigues, Robert M Urban, Joshua J Jacobs, Jeremy L GilbertAbstract:Titanium alloys are widely used in total-joint replacements due to a combination of outstanding mechanical properties, biocompatibility, passivity, and corrosion resistance. Nevertheless, retrieval studies have pointed out that these materials can be subjected to localized or general corrosion in modular interfaces when mechanical abrasion of the oxide film (fretting) occurs. Modularity adds large crevice environments, which are subject to micromotion between contacting interfaces and Differential Aeration of the surface. Titanium alloys are also known to be susceptible to hydrogen absorption, which can induce precipitation of hydrides and subsequent brittle failure. In this work, the surface of three designs of retrieved hip-implants with Ti-6Al-4V/Ti-6Al-4V modular taper interfaces in the stem were investigated for evidence of severe corrosion and precipitation of brittle hydrides during fretting-crevice corrosion in the modular connections. The devices were retrieved from patients and studied by means of scanning electron microscopy (SEM), X-ray diffraction (XRD), and chemical analysis. The surface qualitative investigation revealed severe corrosion attack in the mating interfaces with evidence of etching, pitting, delamination, and surface cracking. In vivo hydrogen embrittlement was shown to be a mechanism of degradation in modular connections resulting from electrochemical reactions induced in the crevice environment of the tapers during fretting-crevice corrosion.
-
in vivo severe corrosion and hydrogen embrittlement of retrieved modular body titanium alloy hip implants
Journal of Biomedical Materials Research Part B, 2009Co-Authors: Danieli C Rodrigues, Robert M Urban, Joshua J Jacobs, Jeremy L GilbertAbstract:Titanium alloys are widely used in total-joint replacements due to a combination of outstanding mechanical properties, biocompatibility, passivity, and corrosion resistance. Nevertheless, retrieval studies have pointed out that these materials can be subjected to localized or general corrosion in modular interfaces when mechanical abrasion of the oxide film (fretting) occurs. Modularity adds large crevice environments, which are subject to micromotion between contacting interfaces and Differential Aeration of the surface. Titanium alloys are also known to be susceptible to hydrogen absorption, which can induce precipitation of hydrides and subsequent brittle failure. In this work, the surface of three designs of retrieved hip-implants with Ti-6Al-4V/Ti-6Al-4V modular taper interfaces in the stem were investigated for evidence of severe corrosion and precipitation of brittle hydrides during fretting-crevice corrosion in the modular connections. The devices were retrieved from patients and studied by means of scanning electron microscopy (SEM), X-ray diffraction (XRD), and chemical analysis. The surface qualitative investigation revealed severe corrosion attack in the mating interfaces with evidence of etching, pitting, delamination, and surface cracking. In vivo hydrogen embrittlement was shown to be a mechanism of degradation in modular connections resulting from electrochemical reactions induced in the crevice environment of the tapers during fretting-crevice corrosion. © 2008 Wiley Periodicals, Inc. J Biomed Mater Res Part B: Appl Biomater, 2009
Danieli C Rodrigues - One of the best experts on this subject based on the ideXlab platform.
-
in vivo severe corrosion and hydrogen embrittlement of retrieved modular body titanium alloy hip implants
Journal of Biomedical Materials Research Part B, 2009Co-Authors: Danieli C Rodrigues, Robert M Urban, Joshua J Jacobs, Jeremy L GilbertAbstract:Titanium alloys are widely used in total-joint replacements due to a combination of outstanding mechanical properties, biocompatibility, passivity, and corrosion resistance. Nevertheless, retrieval studies have pointed out that these materials can be subjected to localized or general corrosion in modular interfaces when mechanical abrasion of the oxide film (fretting) occurs. Modularity adds large crevice environments, which are subject to micromotion between contacting interfaces and Differential Aeration of the surface. Titanium alloys are also known to be susceptible to hydrogen absorption, which can induce precipitation of hydrides and subsequent brittle failure. In this work, the surface of three designs of retrieved hip-implants with Ti-6Al-4V/Ti-6Al-4V modular taper interfaces in the stem were investigated for evidence of severe corrosion and precipitation of brittle hydrides during fretting-crevice corrosion in the modular connections. The devices were retrieved from patients and studied by means of scanning electron microscopy (SEM), X-ray diffraction (XRD), and chemical analysis. The surface qualitative investigation revealed severe corrosion attack in the mating interfaces with evidence of etching, pitting, delamination, and surface cracking. In vivo hydrogen embrittlement was shown to be a mechanism of degradation in modular connections resulting from electrochemical reactions induced in the crevice environment of the tapers during fretting-crevice corrosion.
-
in vivo severe corrosion and hydrogen embrittlement of retrieved modular body titanium alloy hip implants
Journal of Biomedical Materials Research Part B, 2009Co-Authors: Danieli C Rodrigues, Robert M Urban, Joshua J Jacobs, Jeremy L GilbertAbstract:Titanium alloys are widely used in total-joint replacements due to a combination of outstanding mechanical properties, biocompatibility, passivity, and corrosion resistance. Nevertheless, retrieval studies have pointed out that these materials can be subjected to localized or general corrosion in modular interfaces when mechanical abrasion of the oxide film (fretting) occurs. Modularity adds large crevice environments, which are subject to micromotion between contacting interfaces and Differential Aeration of the surface. Titanium alloys are also known to be susceptible to hydrogen absorption, which can induce precipitation of hydrides and subsequent brittle failure. In this work, the surface of three designs of retrieved hip-implants with Ti-6Al-4V/Ti-6Al-4V modular taper interfaces in the stem were investigated for evidence of severe corrosion and precipitation of brittle hydrides during fretting-crevice corrosion in the modular connections. The devices were retrieved from patients and studied by means of scanning electron microscopy (SEM), X-ray diffraction (XRD), and chemical analysis. The surface qualitative investigation revealed severe corrosion attack in the mating interfaces with evidence of etching, pitting, delamination, and surface cracking. In vivo hydrogen embrittlement was shown to be a mechanism of degradation in modular connections resulting from electrochemical reactions induced in the crevice environment of the tapers during fretting-crevice corrosion. © 2008 Wiley Periodicals, Inc. J Biomed Mater Res Part B: Appl Biomater, 2009
K R Stokes - One of the best experts on this subject based on the ideXlab platform.
-
the influence of nickel aluminium bronze microstructure and crevice solution on the initiation of crevice corrosion
Electrochimica Acta, 2008Co-Authors: J A Wharton, K R StokesAbstract:A new mechanistic model has been established for the chemical and electrochemical mechanisms controlling nickel–aluminium bronze crevice corrosion. The crevice corrosion was initially confined to eutectoid regions with slight attack of the copper rich ?-phase within the ?+?III eutectoid. In the presence of high chloride concentrations, copper and aluminium complexes form and the hydrolysis of these complexes leads to the acidification of the crevice solution chemistry. As the crevice solution becomes increasingly acidic the initial protection of the ?-phases due to their higher aluminium contents is lost and become anodic to the ?-phase. The continuous nature of the ?III-phase makes it vulnerable with an 80 ?m depth of attack after only the first month which is accompanied by internal copper redeposited at cathodic sites. Crevice corrosion of copper-based alloys is often reported to be controlled by a copper-ion concentration cell, however, for nickel–aluminium bronze it appears that primarily the crevice corrosion propagation results from a combined action of localised acidification and Differential Aeration between the bold and occluded zones. This mechanistic understanding provides further insights in to the development of crevice corrosion experienced by nickel–aluminium bronze after long-term exposures to natural seawater for up to 3 years.
Danyil Kovalov - One of the best experts on this subject based on the ideXlab platform.
-
prediction of corrosion fatigue crack growth rate in alloys part ii effect of electrochemical potential nacl concentration and temperature on crack propagation in aa2024 t351
Corrosion Science, 2019Co-Authors: Danyil Kovalov, Balazs Fekete, George R Engelhardt, Digby D MacdonaldAbstract:Abstract We report here on the prediction of corrosion fatigue crack growth rate (CFCGR) for Aluminum Alloy 2024-T351 in aqueous environments under cyclical sinusoidal loading. Using the General Corrosion Fatigue Model (GCFM) described in Part I, the CFCGR was calculated as a function of environmental variables, including the electrochemical potential, NaCl concentration, loading frequency, stress intensity factor range, and temperature, in addition to the contribution from mechanical fatigue. Based on the influence of the environment, the changes in the potential drop down the crack enclave and the corrosion current density in a 1:1 electrolyte were also calculated from which the CFCGR was estimated. Corrosion fatigue crack growth in this alloy is readily understood in terms of the competition between environmental factors as described by the Differential Aeration hypothesis and the hydromechanics (advection) of the system resulting from the cyclical opening and closing of the crack.
-
prediction of corrosion fatigue crack growth rate in alloys part i general corrosion fatigue model for aero space aluminum alloys
Corrosion Science, 2018Co-Authors: Danyil Kovalov, Balazs Fekete, George R Engelhardt, Digby D MacdonaldAbstract:Abstract In this work, a General Corrosion Fatigue Model (GCFM) was developed for predicting corrosion fatigue crack growth rate (CFCGR) in metals under cyclical loading. The GCFM is based on an equation for the potential drop from the external surface to the crack tip of metals as derived from the principle of Differential Aeration. Development of the GCFM involves consideration of cyclic loading on the CFCGR and of advection between the in-crack and external environment. We demonstrate the influence of corrosion environment and cyclic loading on the crack growth rate in Al-Li alloys in a 1:1 electrolyte (0.6 M NaCl).