Aluminum Depletion Research Articles

Decision tree-based approach to extrapolate life cycle inventory data of manufacturing processes

Life cycle assessment (LCA) plays a crucial role in green manufacturing to uncover the critical aspects for alleviating the environmental burdens due to manufacturing processes. However, the scarcity of life cycle inventory (LCI) data for the manufacturing processes is a considerable challenge. This paper proposes a novel approach to extrapolate LCI data of manufacturing processes. Taking advantage of LCI data in the Ecoinvent datasets, decision tree-based supervised machine learning models, namely decision tree, random forest, gradient boosting, and adaptive boosting, have been developed to extrapolate the data of GHG emissions, i.e., carbon dioxide, nitrous oxide, methane, and water vapor. Initially, a correlation analysis was conducted to derive the most influential factors on GHG quantities resulting from manufacturing activities. First, the collected data have been preprocessed and split into train and test sets (70% and 30%, respectively). Second, a five-fold cross-validation method was applied to tune the hyperparameters of the models. Then, the models were re-trained using the best hyperparameters and evaluated using the test set. The results reveal that the Gradient Boosting model has a superior predictive performance for extrapolating the GHG emission data, with average coefficients of determination (R2) on the test set <0.95. Moreover, the model predictions involve relatively low values of the average root mean squared error and an average mean percentage of error on the test set. The correlation and feature importance analyses emphasized that the workpiece material and manufacturing technology have a considerable effect on natural resource consumption, i.e., energy, material, and water inflows into the process. Meanwhile, energy consumption, water usage, and raw aluminum depletion were the most influential factors in GHG emissions. Eventually, a case study to extrapolate the inflows and the outflows for new manufacturing activities has been conducted using the validated models. The proposed GraBoost model provides a computational supplementary approach to estimate and extrapolate the GHG emissions for different manufacturing processes when LCI data are incomplete or don't exist within LCI databases.

Delamination of thermally sprayed ZnAl15/organic duplex coating systems on structural steel for offshore wind applications

Duplex coating systems incorporating both thermally sprayed metal (TSM) and organic coatings have demonstrated excellent corrosion protection performance in highly corrosive offshore applications. However, the present work showed extensive delamination of organic coatings from the TSM (ZnAl15) layer during ISO 12944-9 cyclic ageing test. A positive correlation was uncovered between cathode-to-anode ratio and the extent of the delamination, which was further verified by delamination measurement on samples with varying artificial scribes. A depletion of aluminum at the tip of propagating cracks in the TSM layer was detected by scanning electron microscopy (SEM) and energy dispersive X-ray spectroscopy (EDS), suggesting the occurrence of local acidification driven by hydrolysis of Al3+. X-ray diffraction (XRD) analysis confirmed ZnO, Zn5(OH)8Cl2·H2O, and AlO(OH) as the main corrosion products in the artificial scribe. Careful considerations and supplementary real-field assessment were recommended when employing ISO 12944-9 cyclic ageing test for a robust anticorrosive performance evaluation of this type of duplex coating system.

Enhancing the high-temperature corrosion resistance of HVOF-sprayed NiCoCrAlY coating in marine environment by Pt modification and pre-oxidation

To prolong the service lifetime of hot-section components used in marine environment at elevated temperatures, it is crucial to explore and develop high-temperature corrosion-resistant coatings. High-velocity oxygen fuel (HVOF) sprayed NiCoCrAlY, Pt-modified NiCoCrAlY and pre-oxidized Pt-modified NiCoCrAlY coatings were prepared and investigated. This study is concerned with the performance of three coatings in a simulated marine environment based on the phase composition of corrosion products and microstructure evolution of coating samples combined with first-principles density functional theory. The results show that the NiCoCrAlY coating was subject to accelerated corrosion and extensive aluminum depletion, leading to premature coating failure. The high-temperature corrosion resistance of Pt-modified NiCoCrAlY coating was found to be better than that of NiCoCrAlY coating. In contrast, the pre-oxidized Pt-modified NiCoCrAlY coating offered long-lasting protection and exhibited the best corrosion resistance, which is attributed to the positive synergistic effect between Pt modification and pre-oxidation.

The Microstructure Formation of a Protective Oxide-Scale Layer on Small-Diameter FeCrAl Fibers

FeCrAl fibers, at high temperatures, form a protective oxide-scale layer dominated by aluminum oxide on the surface to prevent further oxidation of the base metal alloy. This study investigates the effects of heat treatment on the microstructure formation of the oxide-scale layer on small-diameter FeCrAl fibers, 12 and 17 µm, produced using a bundle drawing process. The morphology examination and chemical analyses of the small-diameter fibers exhibit the microstructure and chemical compositions of the surface and cross-section areas, revealing a distinctive interface layer with a high aluminum concentration between the base metal and the oxide-scale layer. Furthermore, thermogravimetric analysis results show that the 12 µm fibers have about a 60% higher oxidation rate than the 17 µm fibers-caused by the high outward diffusion of aluminum to the surface of the fibers due to their high surface-area-to-weight ratio. Consequently, the high growth rate of the nonuniform oxide-scale layer and the limited aluminum reservoir of the 12 and 17 µm diameter fibers lead to faster depletion of aluminum from the base metal alloy-limiting the lifetime and durability of the smaller-diameter fibers in high-temperature applications.

Comparative study on the initial oxidation behavior of conventional and nanocrystalline MCrAlY coatings - effect of microstructure evolution and dynamic mechanisms

Two MCrAlY coatings with the same nominal composition but different microstructures are prepared by magnetron sputtering (MS) and arc ion plating (AIP). Their oxidation at 1000°C led to very different results. The relatively coarse grained AIP coating formed a duplex-layer scale, consisting of external θ-Al2O3 and internal α-Al2O3, with small amounts of NiCr2O4. Severe surface undulation was accompanied by the development of numerous cracks and voids. Aluminum depletion transformed the AIP coating from β to γ, causing volume shrinkage, promoting scale spallation and leading to premature failure. In contrast, the nanocrystalline MS coating was less degraded due to its columnar crystal structure and high-density of grain boundaries which provided rapid Al diffusion. Oxidation of this coating was characterized by a faster θ-Al2O3 to α-Al2O3 transformation and formation of an exclusive α-Al2O3 scale, protecting the surface.

Mineralogy and geochemical signatures as indicators of differential weathering in natural soil profiles from the West Asturian-Leonese Zone (NW Iberia)

This paper presents detailed mineralogical results together with a geochemical characterization for a sequence of six natural soil profiles. Bedrock samples (R series) and overlying soil samples (S series) were characterized. The soil profiles are distributed in a series of Paleozoic lithological units from lower Ordovician to upper Carboniferous in age (Iberian Massif, NW Iberia). The lithological influence on mineral properties and geochemical composition and, how different weathering may be occurring under very similar temperate and acidic conditions, have been studied. Field observations together with laboratory analyses were indicative of differential weathering. So, a series of selected chemical indices and relations were applied to clarify this assumption. The mineralogy was analysed by Scanning electron microscopy (SEM-EDS), X-ray diffraction (XRD) of rock powder and soil oriented aggregates. X-ray fluorescence spectrometry (XRF) and inductively coupled plasma mass spectroscopy (ICP-MS) were applied to analyse chemical composition. The first results showed how major elements, SiO2, Al2O3 and Fe2O3, slightly enriched in the soil profiles, are consistent with the dominant mineralogy: quartz, chlorite, muscovite and/or illite, together with kaolinite and albite. The bases K2O, Na2O, CaO and MgO are also coherent with mineral composition and experience little variation, but are gradually removed in the profiles. The mobility of major elements leads to a general loss of bases and, in general, a slight enrichment in silica and sesquioxides. SiO2 is enriched, firstly accumulated in soils and partially depleted by dissolution as colloidal form. Al2O3 in some soils is slightly less than in former rocks, so other physical processes are expected to take place, involving clay removal with consequent aluminium depletion too. A special emphasis has been given to albite coexisting with kaolinite, firstly supposed to be directly inherited from parent substrates when present, but finally the chemical index PIA shows it was mainly due to mineral alteration of plagioclases. The best correlations to explain the albite alteration and kaolinitization progress were obtained with chemical indices PIA, CIW, CIA and Al2O3/Na2O ratio. This together with mineralogical signatures, suggest that kaolinite is the result of gradual dissolution due to the acid hydrolysis of albite in such acidic environments, which may also be attributed to the organic matter influence.

Health and Durability of Protective and Thermal Barrier Coatings Monitored in Service by Visual Inspection

Protective and Thermal Barrier Coatings (TBC) applied on gas-turbine blades gradually degrade due to oxidation, aluminum depletion and impacts of environmental particles. Among various non-destructive coating testing methods (NDT), visual inspection can be undertaken regularly in service, but it provides little quantitative information, and only surface defects can be detected. This work aims at in-service monitoring of turbine blades with multilayer coatings applied by atmospheric plasma spraying (APS) in a few variants. They were validated during a series of accelerated mission tests of a retired military turbofan engine in a test cell together with five other technologies. The fifty-hour rainbow test focused on assessing coating durability. Between engine runs, 12 borescope inspections were conducted to monitor the health of the blades. Finally, the blades were disassembled and examined using computed tomography (CT) and metallographic methods. Throughout the testing, 31 newly-coated blades (66%) withstood the tests, producing results comparable to the reference blades. However, 16 blades suffered intolerable failures observed as increased roughness, gradual loss of the topcoat, spallation and minor foreign object damage. Visual inspection results were generally in agreement with subsequent laboratory tests.

Isothermal short‐term oxidation behavior of MAR‐M246 nickel‐based superalloy at 800°C and 1000°C

AbstractSuperalloys are widely employed at high temperatures for structural applications. Hence, knowledge about the oxidation of these materials is essential. However, the literature is scanty when it comes to some families of superalloys. The purpose of this study was therefore to analyze the MAR‐M246 polycrystalline alloy in isothermal short‐term tests at 800°C and 1000°C for up to 240 h. Thermodynamic simulations were performed to evaluate the material's phase stability as a function of temperature and to assess the expected phases in response to oxygen pressure. The oxidized samples were characterized by SEM‐EDS and DRX, which revealed a tendency for scaling of oxidized material, particularly at temperatures of 1000°C. Nevertheless, protective layers of Cr2O3 and Al2O3 oxides were formed, which enabled the formation of fairly thin oxide layers, in addition to NiO and complex oxides. The region of the metallic substrate close to the oxide layer underwent aluminum depletion, causing the gamma‐prime phase to disappear, as well as formation of aluminum oxides and titanium nitrides. Last, a good correlation was found between the thermodynamic simulations and the oxides that were formed.

Aluminum depletion induced by co-segregation of carbon and boron in a bcc-iron grain boundary

The local variation of grain boundary atomic structure and chemistry caused by segregation of impurities influences the macroscopic properties of polycrystalline materials. Here, the effect of co-segregation of carbon and boron on the depletion of aluminum at a Σ5 (3 1 0 )[0 0 1] tilt grain boundary in a α − Fe-4 at%Al bicrystal is studied by combining atomic resolution scanning transmission electron microscopy, atom probe tomography and density functional theory calculations. The atomic grain boundary structural units mostly resemble kite-type motifs and the structure appears disrupted by atomic scale defects. Atom probe tomography reveals that carbon and boron impurities are co-segregating to the grain boundary reaching levels of >1.5 at%, whereas aluminum is locally depleted by approx. 2 at.%. First-principles calculations indicate that carbon and boron exhibit the strongest segregation tendency and their repulsive interaction with aluminum promotes its depletion from the grain boundary. It is also predicted that substitutional segregation of boron atoms may contribute to local distortions of the kite-type structural units. These results suggest that the co-segregation and interaction of interstitial impurities with substitutional solutes strongly influences grain boundary composition and with this the properties of the interface.

The formation mechanism, growth, and effect on the mechanical properties of precipitate free zones in the alumina-forming austenitic stainless steel Fe–20Cr–30Ni–2Nb–5Al during creep

The mechanisms of formation and growth of L12 precipitate-free zones (PFZs) in the alumina-forming austenitic stainless steel Fe–20Cr–30Ni–2Nb–5Al during creep were studied using scanning electron microscopy and energy dispersive x-ray spectroscopy. The PFZs formed following the dissolution of L12 precipitates due to depletion of nickel and aluminum. Little PFZ growth occurred until the grain boundaries were substantially covered by Laves phase and B2 precipitates large enough to deplete the surrounding grain of nickel and aluminum. This resulted in the dissolution of the L12 precipitates. Additionally, micro-cracks observed in the PFZ at long creep times suggest that the PFZ is ultimately the weakest point in the microstructure, and that fracture initiates there.

Transition properties of a2Σ–, b2Δ, c2Π, d2Π, and e2Σ+ electronic states of aluminum silicon radical

Detecting aluminum silicon can yield useful information concerning the depletion of silicon and aluminum and their recycling in astrophysical sources. In addition, such detection can be helpful for understanding gas–phase aluminum and silicon chemistry in the interstellar/circumstellar atmosphere. However, only a few transition properties of this radical have been reported. Therefore, the potential energy curves of several lowest–lying doublet states and the transition dipole moments between them were calculated using the icMRCI approach. Core–valence correlation correction, scalar relativistic correction, and spin–orbit coupling effect were included to improve the accuracy of transition properties. The radiative lifetimes of the first 16 levels were approximately 4.8 – 679.5 ms for the c2Π1/2 state, 2.2 – 431 ms for the c2Π3/2 state, 29.3 – 40.4 µs for the d2Π1/2 state, 21.2 – 30.1 µs for the d2Π3/2 state, and 88.7 – 175.6 µs for the e2Σ+1/2 state. The spontaneous emissions from the c2Π1/2 and c2Π3/2 states to the a2Σ–1/2, b2Δ3/2, and b2Δ5/2 states and those from the e2Σ+1/2 state to the d2Π1/2 and d2Π3/2 states were located in the radio–frequency region. The d2Π1/2 – a2Σ–1/2 and d2Π3/2 – a2Σ–1/2 transitions were the strongest, followed by d2Π1/2 – b2Δ3/2, d2Π3/2 – b2Δ3/2, d2Π3/2 – b2Δ5/2, d2Π1/2 – c2Π1/2, d2Π3/2 – c2Π3/2, e2Σ+1/2 – c2Π1/2, and e2Σ+1/2 – c2Π3/2 transitions. The spontaneous emissions from these systems were located in the infrared region. The variation in the radiative lifetime of a level υ versus the rotational quantum number J was investigated for the d2Π1/2, d2Π3/2, and e2Σ+1/2 states.

Evidence of formation of an amorphous magnesium silicate (AMS) phase during alkali activation of (Na-Mg) aluminosilicate glasses

There is some ambiguity regarding the fate of Mg during the alkali activation of Mg-rich precursors within the broader field of alkali activated materials (AAMs). The present work addresses this issue by studying the reaction products in AAMs synthesized from (Na-Mg) aluminosilicate glasses. Here, instead of magnesium silicate hydrate (M-S-H) phase, Mg exclusively forms an amorphous magnesium silicate (AMS) phase. Compared to M-S-H, AMS is a more depolymerized phase, which has not previously been well documented. The formation of AMS seems to be driven by the high charge density of the Mg cation which effectively stabilizes the depolymerized silicate species. We also show that the lack of hydrotalcite-group phases is due to aluminum depletion by zeolite formation. This work highlights the need to consider the existence of the AMS phase in Mg-containing AAMs, especially in complex systems, where its identification may be difficult.

Structural transformations of a gas-atomized Al62.5Cu25Fe12.5 alloy during detonation spraying, spark plasma sintering and hot pressing

In this work, we traced structural transformations of an Al62.5Cu25Fe12.5 alloy, in which a quasicrystalline icosahedral phase (i-phase) can be formed, upon spraying onto a substrate and consolidation from the powder into the bulk state. The Al62.5Cu25Fe12.5 powder was obtained by gas atomization and consisted of i-phase and ?-phase AlCu(Fe). The powder was detonation sprayed (DS) and consolidated by spark plasma sintering (SPS)/hot pressing (HP). During DS, the particles experienced partial or complete melting and rapid solidification, which resulted in the formation of coatings of a complex structure. The composite regions containing i-phase were inherited from the powder alloy. The fraction of the material that experienced melting solidified as ?-phase AlFe(Cu) in the coating. It was suggested that the difficulty of obtaining i-phase upon post-spray annealing is related to aluminum depletion of the alloy during DS. During SPS and HP, the elemental composition of the alloy was preserved, while the exposure to an elevated temperature led to phase homogenization. SPS and HP conducted at 700?C resulted in full densification and the formation of a single-phase quasicrystalline alloy. The sintered single-phase alloy showed a higher microhardness in comparison with the DS coatings.

Influence of ferritic nitrocarburizing on the high-temperature corrosion-fatigue properties of the Si-Mo-Al cast iron SiMo1000

The influence of ferritic nitrocarburizing on the high-temperature corrosion-fatigue properties of the Si-Mo-Al cast iron SiMo1000 is investigated in the present study. It was found that nitrocarburizing effectively increases the surface hardness, but dramatically decreases the fatigue and oxidation resistance of SiMo1000. The fatigue resistance is reduced due to two types of microcracks formed after nitrocarburizing. The oxidation resistance is dramatically diminished due to the formation of microcracks, and the depletion of aluminum in the matrix from nitride precipitation during the exposure at 800 °C. The corrosion-fatigue synergy is found to cause severe decarburization (i.e. graphite depletion) in nitrocarburized SiMo1000.

Influence of codoping with Hf and La on grain‐boundary transport in alumina

AbstractThe role of reactive elements (RE) is an important topic in understanding the oxidation behavior of high‐temperature alloys. In this work, the influence of codoping alumina with two different RE elements (500 ppm Hf + 500 ppm La) was studied. The kinetics of oxygen grain‐boundary (GB) transport were studied at 1400°C using metallic nickel particles as markers. The results were compared with data obtained on the corresponding singly doped compositions; alumina‐500 ppm La, and alumina‐500 ppm Hf. The results showed that singly doping with La did not have any benefit compared to undoped alumina, whereas singly doping with Hf resulted in a slowing of transport by a factor of ~7. The behavior of the codoped sample was very similar to that of the singly doped Hf composition. For all the studied compositions, atomic scale characterization using high‐angle annular dark‐field scanning transmission electron microscopy and atom probe tomography (APT) revealed strong segregation of the dopant ions to the alumina grain boundaries. In the codoped sample, APT revealed evidence of oxygen excess and aluminum depletion at the GB core.

The influence of near service environmental conditions on the corrosion and LCF behaviour of a beta-stabilized γ-TiAl alloy

The damage behaviour of the TiAl alloy Ti-43.5Al-4Nb-1Mo-0.1B was investigated by isothermal thermogravimetric-analysis (TGA) and strain controlled low-cycle-fatigue (LCF) experiments at high temperature. Aluminium depletion and the formation of a continuous brittle layer in the subsurface zone takes place in synthetic exhaust gas. Contrary, a continuous ductile γ-phase forms in the subsurface zone in air. Since a continuous TiN layer as diffusion barrier is not formed in the early stages of corrosion, strong hardening is observed in LCF test samples in exhaust gas and a strain amplitude of 0,6 %, leading to a significant reduction of the cycles to failure.

Kolaviron stimulates glucose uptake with concomitant modulation of metabolic activities implicated in neurodegeneration in isolated rat brain, without perturbation of tissue ultrastructural morphology

Reduced glucose uptake usually occurs in type 2 diabetes due to down-regulation of brain glucose transporters. The potential of kolaviron, a biflavonoid from Garcinia kola to stimulate glucose uptake and suppress glucose-induced oxidative toxicity were investigated in rat brain. Its molecular interactions with the target proteins were investigated in silico. Kolaviron was incubated with excised rat brain in the presence of glucose for 2 h, with metformin serving as a positive control. Kolaviron caused a significant (p < 0.05) increase in glucose uptake, glutathione level, superoxide dismutase, catalase, ATPase, ENTPDase and 5’-nucleotidase activities, while concomitantly depleting malondialdehyde level, acetylcholinesterase and butyrylcholinesterase activities compared to brains incubated with glucose only. Electron microscopy (SEM and TEM) analysis revealed kolaviron had little or no effect on the ultrastructural morphology of brain tissues as evidenced by the intact dendritic and neuronal network, blood vessels, mitochondria, synaptic vesicles, and pre-synaptic membrane. SEM-EDX analysis revealed a restorative effect of glucose-induced alteration in brain elemental concentrations, with total depletion of aluminum and zinc. MTT analysis revealed kolaviron had no cytotoxic effect on HT-22 cells. Molecular docking revealed a potent interaction between kolaviron and catalase at the SER114 and MET350 residues, with a binding energy of 12 kcal/mol. Taken together, these results portray the potential of kolaviron to stimulate glucose uptake while concomitantly coffering a neuroprotective effect.

Modeling and characterisation of depletion of aluminium in bond coat and growth of mixed oxides in thermal barrier coatings

Most existing thermal barrier coating (TBC) studies do not account for the depletion of Al in the BC and growth of mixed oxides (MOs). In this complementary study, we modify and extend our earlier (Lim and Meguid in Mater Des, 2019. https://doi.org/10.1016/j.matdes.2018.107543 ) coupled finite volume (FV)–finite element (FE) formulations to incorporate diffusion reactions of Al and Cr in the BC. The modified/expanded FV–FE formulations are supported by the introduction of appropriate diffusion–reaction equations and high temperature oxidation model. Three aspects of the work were accordingly examined. Firstly, the FV model is used to describe the diffusion and reaction of Al and O2 in the formation of α-Al2O3. The β-phase rate of depletion predicted by the model agrees well with experimental findings. Secondly, the diffusion of Cr through the TGO that leads to the formation of an external layer of MOs is simulated using the FV model. Our simulations reveal that MOs form in the early stage of thermal exposure, although there are sufficient Al in the BC to sustain the growth of α-Al2O3 phase. We reasoned this to the formation of internal oxides and diffusion cell in the BC. Lastly, we studied the effect of roughness on β-phase depletion and growth of TGO (α-Al2O3 + MOs). We show that β-phase in the peak of undulation depletes faster and the interface between the β + γ phase and γ phase in the BC straightens over time. Furthermore, our results reveal that MOs tend to form in the valley of undulation due to the shorter diffusion path.

Oxidation Behavior of Nanostructured Ni-5Al Coating. A case Study on Monophase Coatings

Oxidation behavior of nanostructured Ni-5Al HVOF coatings was studied. For this purpose, isothermal oxidation of the free standing coatings was performed at 950°C. Lattice parameter determination technique was used for evaluating aluminum depletion to characterize oxidation behavior. The results showed that Al-depletion rate of the nanostructured coating was less than that of the conventional one, suggesting superior oxidation resistance of the nanostructured one. One reason, besides the one usually ascribed to grain size refinement and distribution of Nano oxides, lies in the coating integrity which imply the absence of any notable discontinuities including inter-splat oxides and porosities. On the other hand, vacuum heat treatment revealed that the nanostructured coating exhibited a phenomenon called diffusional creep, which is thought to be the most effective one in all densification mechanisms responsible for metallurgical consolidation processes. It was argued that this mechanism must also be active during oxidation in air and therefore can help retain the coating integrity, providing a sound metallic base for durable surface supply of aluminum throughout oxidation process. Therefore, coating integrity also is central to the formation of the protective α-Al2O3 subscale, as observed and argued in this paper for the nanostructured Ni-5Al coating.

Effect of the Cobalt Content and Chromium Alloying on the Structure of the Scale Formed on Structural β-NiAl + γ'-Ni3Al + γ-Ni Alloys (Ni–Al–Co System) at 1300°C

The structures of the scale and the subscale layers that form during the air oxidation of the β + γ' + γ alloys of the Ni–Al–Co system containing (at %) ~27 Al (alloys 1–3), 10 Co (base alloy 1), 16 Co (alloy 2), and 10 Co and 4.25 Cr (alloy 3) at 1300°C for 100 h are studied. The formation of scale (Al2O3) in all alloys leads to the aluminum depletion of the subscale layers and to the γ' → γ + γ' transition due to the interdiffusion of aluminum and oxygen. An increase in the cobalt content from 5 to 10 at % increases the heat resistance. The degradation of the heat resistance induced by an increase in the cobalt content to 16 at % is related to an increase in the volume fraction of the γ phase in an alloy as compared to the base alloy with 10 at %. The introduction of small amounts of chromium degrades the heat resistance because of the development of internal oxidation, i.e., the penetration of alumina into an alloy along interdendritic γ-phase precipitates. The heat resistance of the chromium-free β + γ' + γ alloy with 10 at % Co at 1300°C, which was estimated from the sample mass increment per unit surface area in 100 h, is higher than the heat resistance of the well-known γ' + γ VKNA and VIN alloys at 1100–1200°C.