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Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.

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At least 37 records · Page 2
All sourcesNASA NTRSDOE OSTI
DOE OSTI2024

A Multiscale Inelastic Internal State Variable Corrosion Model

We present a corrosion internal state variable (ISV) damage model based upon the integrated computational materials engineering (ICME) hierarchical multiscale paradigm. Structure–property experiments for magnesium alloys were used where the only inputs were the volume fractions of each element of the periodic table. This macroscale ISV corrosion model finds its basis in Horstemeyer’s mechanical damage model, which includes three separate ISVs for damage nucleation, growth, and coalescence, as well as Walton’s inclusion of corrosion, which introduces five new ISVs for pit nucleation, growth, and coalescence, along with general corrosion and intergranular corrosion. While Walton’s corrosion ISVs are phenomenological in nature, herein we develop a multiscale physical basis for the corrosion ISVs. The parameters for the macroscale corrosion ISVs were garnered from the mesoscale Butler–Volmer equations. Pure magnesium with differing amounts of aluminum were used in corrosion tests to exemplify the different pitting, general corrosion, and intergranular corrosion rates, and the macroscale ISV model was calibrated with said data, in which the only inputs to the model are the volume percentages of the elements magnesium and aluminum. Although magnesium alloys were used to motivate and calibrate the model, the model is abstract enough to possibly capture other material systems as well.

Chemistry↗
DOE OSTI2018

Grain boundary selective oxidation and intergranular stress corrosion crack growth of high-purity nickel binary alloys in high-temperature hydrogenated water

The effects of alloying elements in Ni-5at%X binary alloys on intergranular (IG) corrosion and stress corrosion cracking (SCC) have been assessed in 300-360°C hydrogenated water at the Ni/NiO stability line. Alloys with Cr or Al additions exhibited grain boundary oxidation and IGSCC, while localized degradation was not observed for pure Ni, Ni-Cu or Ni-Fe alloys. Environment-enhanced crack growth was determined by comparing the response in water and N2 gas. Results demonstrate that selective grain boundary oxidation of Cr and Al promoted IGSCC of these Ni alloys in hydrogenated water.

Environmental Molecular Sciences Laboratory↗
DOE OSTI2018

Effects of In Situ Intermetallics on the Microstructural Array and Saline Corrosion Performance of Cast Al/WCp Composites

Al-matrix composites, ex situ reinforced with WC nanoparticles and in situ reinforced with Al{sub 3}(Ti,W), Al{sub 12}W, Al{sub 5}W and Al{sub 4}W, have been fabricated by casting assisted by K{sub 2}TiF{sub 6} wetting agent addition and mechanical stirring. A satisfactory particle incorporation and distribution accompanied by a high reactivity have been attained. The presence, topography, chemical composition of all included phases and their occurrence as clusters or single particles are clarified and justified. Al{sub 12}W is the predominant aluminide phase at WC ≤ 1.5 vol.%. Al{sub 4}W (primarily) and Al{sub 5}W (secondarily) are the predominant aluminide phases at WC ≥ 2.0 vol.%. WC nanoparticles have acted as heterogeneous nucleation sites to Al{sub 3}Ti particles. Reverse polarization tests in 3.5 wt.% NaCl show that the governing form of corrosion is intergranular corrosion of Al around Al{sub 3}FeSi{sub 2} eutectic, fine plates. The corrosion steps/mechanisms are identified. Clusters of aluminides and carbide nanoparticles, as well as intergranular WC nano-dispersoids and their Al-matrix have remained corrosion-free. The role of the aluminides combined with WC remaining nano-cores as inhibitors of the eutectic Al{sub 3}FeSi{sub 2} cathodic activity is highlighted.

36 MATERIALS SCIENCE↗
DOE OSTI2024

How irradiation promotes intergranular stress corrosion crack initiation

Irradiation assisted stress corrosion cracking (IASCC) is a form of intergranular stress corrosion cracking that occurs in irradiated austenitic alloys. It requires an irradiated microstructure along with high temperature water and stress. The process is ubiquitous in that it occurs in a wide range of austenitic alloys and water chemistries, but only when the alloy is irradiated. Despite evidence of this degradation mode that dates back to the 1960s, the mechanism by which it occurs has remained elusive. Here, using high resolution electron backscattering detection to analyze local stress-strain states, high resolution transmission electron microscopy to identify grain boundary phases at crack tips, and decoupling the roles of stress and grain boundary oxidation, we are able to unfold the complexities of the phenomenon to reveal the mechanism by which IASCC occurs. The significance of the findings impacts the mechanical integrity of core components of both current and advanced nuclear reactor designs worldwide.

36 MATERIALS SCIENCE↗
NASA NTRS1975

Corrosion and fatigue of surgical implants

Implants for the treatment of femoral fractures, mechanisms leading to the failure or degradation of such structures, and current perspectives on surgical implants are discussed. Under the first heading, general usage, materials and procedures, environmental conditions, and laboratory analyses of implants after service are considered. Corrosion, crevice corrosion, stress corrosion cracking, intergranular corrosion, pitting corrosion, fatigue, and corrosion fatigue are the principal degradation mechanisms described. The need for improvement in the reliability of implants is emphasized.

Lisagor, W. B.↗
NASA NTRS2001

An Electrochemical Framework to Explain Intergranular Stress Corrosion Cracking in an Al-5.4%Cu-0.5%Mg-0.5%Ag Alloy

A modified version of the Cu-depletion electrochemical framework was used to explain the metallurgical factor creating intergranular stress corrosion cracking susceptibility in an aged Al-Cu-Mg-Ag alloy, C416. This framework was also used to explain the increased resistance to intergranular stress corrosion cracking in the overaged temper. Susceptibility in the under aged and T8 condition is consistent with the grain boundary Cu-depletion mechanism. Improvements in resistance of the T8+ thermal exposure of 5000 h at 225 F (T8+) compared to the T8 condition can be explained by depletion of Cu from solid solution.

Little, D. A.↗
DOE OSTI2019

Corrosion Behavior of Laser-Brazed Surface Made by Joining of AA6082 and Galvanized Steel

In the present study, a galvanized steel and a AA6082 aluminum alloy sheet of 2 mm thick were weld-brazed by applying laser and using 2-mm-diameter solid Al-12% Si filler wire at 2.5 m/min wire feed rate and 2 m/min laser scan speed at varying laser power (4.0, 3.5, 3.0 kW) in flange configuration. The microstructural investigation of the laser weld-brazed joints revealed the presence of two-layered intermetallic compound at steel/braze seam interface. The corresponding x-ray diffraction analysis of the steel/braze seam interface showed the presence of Al-Fe-Si-based ternary intermetallic phases. SEM and EDS analysis of the braze seam revealed the presence of α-Al grains surrounded by Mg{sub 2}Si phase in the grain boundary region. Fine intermetallic layer was observed at lower heat-input condition. The corrosion performance of the brazed joints was studied with the help of immersion, salt spray, and electrochemical polarization tests in different electrolytes containing NaCl salt. Brazed joints experienced galvanic corrosion during immersed in corrosive media. From the salt spray test, it was revealed that galvanized steel was highly susceptible to corrosion compared to Al-rich phase. The polarization results showed a substantial change in corrosion resistance from steel interface to the brazed region due to the variation in microstructure. The samples brazed with low heat-input showed better corrosion resistance as compared to the joints made with high heat-input. Post-corrosion microstructure revealed intergranular corrosion at the brazed joint along with pit formation.

36 MATERIALS SCIENCE↗
DOE OSTI2019

Mechanical Properties and Corrosion Behavior of AA5754-AA6061 Dissimilar Aluminum Alloys Welded by Cold Metal Transfer

The trend of using lightweight materials in the automotive industry brings along the necessity of dissimilar welding of aluminum alloys such as AA5754 and AA6061. Hybrid structures in automobiles are subjected not only to mechanical forces but also corrosive effects of the environment. In this study, cold metal transfer welding, which is suitable for welding thin sheets and dissimilar materials, was applied to join AA5754 to AA6061. It was aimed to investigate the effect of weld heat input on mechanical properties and corrosion rate measured by the Tafel extrapolation method in 3.5 wt.% NaCl solution at room temperature. The tensile strength of AA5754-AA6061 joints tended to reduce with increasing heat input. Corrosion test results showed that the increased heat input decreased the corrosion resistance and caused intergranular corrosion besides pitting corrosion.

36 MATERIALS SCIENCE↗
DOE OSTI2018

Decoupling the role of stress and corrosion in the intergranular cracking of noble-metal alloys

Intergranular stress-corrosion cracking (IGSCC) is a form of environmentally induced crack propagation causing premature failure of elemental metals and alloys. It is believed to require the simultaneous presence of tensile stress and corrosion; however, the exact nature of this synergy has eluded experimental identification. For noble metal alloys such as Ag–Au, IGSCC is a consequence of dealloying corrosion, forming a nanoporous gold layer that is believed to have the ability to transmit cracks into grain boundaries in un-dealloyed parent phase via a pure mechanical process. Here using atomic-scale techniques and statistical characterizations for this alloy system, we show that the separate roles of stress and anodic dissolution can be decoupled and that the apparent synergy exists owing to rapid time-dependent morphology changes at the dealloyed layer/parent phase interface. We discuss the applicability of our findings to the IGSCC of important engineering Fe- and Ni-based alloys in critical applications.

36 MATERIALS SCIENCE↗
DOE OSTI2018

Effect of Welding Parameters on the Corrosion Behavior of Dissimilar Alloy Welds of T6 AA6061 Al-Galvanized Mild Steel

Partial replacement of steel by Aluminium (Al) alloys is a promising approach adopted by automotive sector to improve fuel efficiency without compromising on the strength. However, this results in the generation of dissimilar welds of Al alloys and steel. Understanding the corrosion behavior of Al alloys–steel welds as a function of welding parameters is critical in the successful application of such alloys. The present study reports the intergranular corrosion behavior of T6 heat-treated AA6061 Al alloy-galvanized mild steel lap joints, welded by metal inert gas welding–brazing technique as a function of different welding parameters, viz. weld speed (4-6 m/min) and wire feed rate (0.8-0.9 m/min), following ASTM G 67-04. Weld characterization was performed by field emission scanning electron microscopy (FESEM), x-ray diffraction and nano-hardness measurement. Results indicate heavy dissolution and metal loss at the interface. A high volume fraction of Al-Fe intermetallics was precipitated at the weld interfaces, resulting in high hardness and higher localized corrosion. The thickness of Al-Fe intermetallic layer increased with increasing wire feed rate and lower weld speed which enhanced the severity of galvanic and intergranular corrosion.

36 MATERIALS SCIENCE↗
DOE OSTI2018

Influences of Quench Cooling Rate on Microstructure and Corrosion Resistance of Al-Cu-Mg Alloy Based on the End-Quenching Test

To investigate the effects of the quench cooling rate on corrosion resistance of Al-Cu-Mg alloy, an end-quenching test was conducted and the microstructures at different cooling rates were observed by SEM and TEM. Additionally, the corrosion resistance was characterized by an intergranular corrosion test and electrochemical test. Moreover, the finite element method was applied to simulate the end quenching process. The results indicate that the actual end quenching process can be approximated as one-dimensional heat transfer, and the cooling rate varies at different cooling distances. By affecting the microstructures, decreasing the cooling rate leads to a decline in the corrosion properties. Low cooling rates coarsen the constituent particles and grain boundary particles, resulting in a wide precipitation-free zone and an increase in the intensity of corrosion reactions. A high cooling rate concentrates on the intragranular precipitant, which can reduce the pitting depth and represents a conversion from localized corrosion to general corrosion.

36 MATERIALS SCIENCE↗
DOE OSTI2018

Intergranular Stress Corrosion Crack Initiation and Temperature Dependence of Alloy 600 in Pressurized Water Reactor Primary Water

Stress corrosion crack (SCC) initiation of a solution annealed, cold-worked (CW) UNS N06600 (Alloy 600) material was investigated in 360 and 325ºC simulated PWR primary water using constant load tensile instrumented for in-situ detection by the direct current potential drop technique. This CW material with high boron and low carbon bulk concentrations was found to be highly susceptible to SCC. Consistent SCC initiation times were obtained at both temperatures and the thermal activation energy for SCC initiation is estimated at ~116 kJ/mol.

Zhai, Ziqing↗
DOE OSTI2024

Corrosion mechanism of cold forged 316 stainless steel in molten FLiNaK salt

This study examined how cold forging (CF) affects the corrosion of 316 stainless steel (SS) in molten FLiNaK salt at 700 °C for 48 h. CF samples had two corrosion areas: one near the top and another displaying intergranular corrosion (IGC). Samples with lower CF (5–30 %) showed more IGC, while the 50 % CF sample had less IGC but the shallowest corrosion depth. This was due to the increased number of grain boundaries, which raised the potential corrosion initiation sites, and certain grain boundaries promoting chromium dissolution, thus enhancing IGC.

FLiNaK↗