Aluminum Segregation Research Articles

Microstructural Properties of Heat-Treated LENS In Situ Additively Manufactured Titanium Aluminide

This study reports on the microstructure, phase identification and hardness property of the LENS-manufactured binary Ti-Al alloy which was achieved via laser in situ alloying. The in situ alloying method, using laser beam as an energy source, indicated that it is possible to achieve a binary gamma phase microstructure from elemental powders of Ti and Al. The as-produced sample, however, was characterized of having different microstructure at the top, middle and bottom regions. The middle and top layers had similar hardness which was lower than that of the bottom region. The as heat-treated sample was characterized of lamellar grain microstructure at the top and just grains at the bottom and the middle. The observed grains were different in size, phase and hardness. This study indicated that in addition to the pores and the precipitation of α2 phase or aluminum segregation on the grain boundary veins intermetallics lead to severe cracking. Overall, the hardness values of the as-produced and heat-treated samples were similar, and due to extensive cracking, it was inferred that both samples will lack ductility.

Influence of Aluminum Coatings on the Quality of Weld Joints

The application of a longitudinal magnetic field in welding aluminum coated sheet is considered. A special welding head is used to produce weld joints of satisfactory quality. Findings are obtained regarding the formation and metallographic structure of the metal in the seam, with the segregation of aluminum over its cross section. The formation of composite structure is noted.

Self-organized carbon-rich stripe formation from competitive carbon and aluminium segregation at Fe0.85Al0.15(1 1 0) surfaces

By combining Scanning Tunnelling Microscopy, Low Energy Electron Diffraction and X-ray Photoelectron Spectroscopy, it was found that the surface of A2 random alloy Fe0.85Al0.15(110) is significantly influenced by the segregation of aluminium but also of carbon bulk impurities. Below ∼900 K, carbon segregates in the form of self-organized protruding stripes separated by ∼5 nm that run along the [001]B bulk direction and cover up to 34% of the surface. Their C 1s spectroscopic signature that is dominated by graphitic carbon peaks around 900 K. Above this temperature, the surface carbon concentration decays by redissolution in the bulk, whereas an intense aluminium segregation is observed giving rise to a hexagonal superstructure. The present findings is interpreted by a competitive segregation between the two elements.

Solidification Mechanism of the D-Gun Sprayed Fe-Al Particles

AbstractThe detonation gas spraying method is used to study solidification of the Fe-40Al particles after the D-gun spraying and settled on the water surface. The solidification is divided into two stages. First, the particle solid shell forms during the particle contact with the surrounding air / gas. Usually, the remaining liquid particle core is dispersed into many droplets of different diameter. A single Fe-Al particle is described as a body subjected to a rotation and finally to a centrifugal force leading to segregation of iron and aluminum. The mentioned liquid droplets are treated as some spheres rotated freely / chaotically inside the solid shell of the particle and also are subjected to the centrifugal force. The centrifugal force, and first of all, the impact of the particles onto the water surface promote a tendency for making punctures in the particles shell. The droplets try to desert / abandon the mother-particles through these punctures. Some experimental evidences for this phenomenon are delivered. It is concluded that the intensity of the mentioned phenomenon depends on a given droplet momentum. The droplets solidify rapidly during their settlement onto the water surface at the second stage of the process under consideration. A model for the solidification mechanism is delivered.

Design of co-existence parallel periodic surface structure induced by picosecond laser pulses on the Al/Ti multilayers

Formation of periodic nanostructures on the Ti/5x(Al/Ti)/Si multilayers induced by picosecond laser pulses is studied in order to better understand the formation of a laser-induced periodic surface structure (LIPSS). At fluence slightly below the ablation threshold, the formation of low spatial frequency-LIPSS (LSFL) oriented perpendicular to the direction of the laser polarization is observed on the irradiated area. Prolonged irradiation while scanning results in the formation of a high spatial frequency-LIPSS (HSFL), on top of the LSFLs, creating a co-existence parallel periodic structure. HSFL was oriented parallel to the incident laser polarization. Intermixing between the Al and Ti layers with the formation of Al-Ti intermetallic compounds was achieved during the irradiation. The intermetallic region was formed mostly within the heat affected zone of the sample. Surface segregation of aluminium with partial ablation of the top layer of titanium was followed by the formation of an ultra-thin Al2O3 film on the surface of the multi-layered structure.

Recycling and segregation of used aluminium beverage cans according to the residents of Silesia voivodship

Abstract Aluminium is one of raw materials that can be practically continuously recycled. Thanks to the proper sorting of aluminium scrap it is possible to produce precisely the same products that it was made before Selective waste collection and an extensive network of waste collection points have significant impact on the recovery level of used aluminium beverage cans. The purpose of the article was to analyse the results of surveys on aluminium segregation in Silesia voivodship. According to literature people are increasingly interested in environmental protection and what is happening with waste generated by them. But there is lack of information about people from different regions of Poland. From the research presented in the paper it can be concluded that people realize that used aluminium beverage cans become packaging waste which can be easily recycled so most of them segregate them in everyday life. This is the result of changes in the legislation on municipal waste and their segregation, as well as the element of environmental education.

Nanocrystalline aluminium particles inside Mg-4Li-4Al-2RE magnesium alloy after severe plastic deformation

Detailed microstructure characterization of ultra-fine grained LAE442 magnesium alloy processed by ECAP was performed by transmission electron microscopy and positron annihilation spectroscopy. Formation of FCC aluminium particles in the magnesium matrix and intensive segregation of aluminium at dislocations was observed. In situ annealing in the transmission electron microscope together with the analysis of the positron annihilation spectrum showed the limited stability of Al particles and Al segregation at temperatures below the processing temperature. It was suggested that the formation of observed Al nanoparticles is caused by the synergic effect of high external stresses during ECAP and the presence of Li atoms dissolved in the Mg matrix.

Microstructure and tensile behavior of 2D-Cf/AZ91D composites fabricated by liquid–solid extrusion and vacuum pressure infiltration

2D carbon fiber reinforced AZ91D matrix composites (2D-Cf/AZ91D composites) were fabricated by liquid–solid extrusion and vacuum pressure infiltration technique (LSEVI). In order to modify the interface between fibers and matrix and protect the fiber, pyrolytic carbon (PyC) coating was deposited on the surface of T700 carbon fiber by chemical vapor deposition (CVD). Microstructure observation of the composites revealed that the composites were well fabricated by LSEVI. The segregation of aluminum at fiber surface led to the formation of Mg17Al12 precipitates at the interface. The aluminum improved the infiltration of the alloy and PyC coating protected the fibers effectively. The ultimate tensile strength of 2D-Cf/AZ91D composites was about 400MPa. The fracture process of 2D-Cf/AZ91D composites was transverse fiber interface cracking–matrix transferring load–longitudinal fibers bearing load–longitudinal fibers breaking.

Aluminum and antimony segregation on a batch hot-dip galvanized Zn-0.05Al-0.2Sb coating

Segregation of aluminum and antimony of spangles on a batch hot-dip galvanized Zn-0.05Al-0.2Sb coating were investigated by scanning electron microscopy (SEM) in backscattered electron mode and with energy dispersive spectrometry, X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS). Results showed that the coating surface displays shiny, feathery and dull spangles, in which considerable metallic oxides and precipitates are detected on coating surface. The metallic oxides on coating surface are identified as mainly ZnO and Al2O3, whilst the nature of the precipitates is identified as Sb3Zn4. Aluminum and antimony are enriched in layers within a thickness of 10–20 nm underneath the outer surface of the coating. The segregation behavior of aluminum and antimony is studied and discussed in terms of the solidification process of the coating.

Segregation as a driving force in the formation of nanocomposite ZrO2-Al2O3 coatings

ZrO2-Al2O3 coatings were deposited on a floating substrate at a temperature of 370°C. Various coating compositions, ranging from pure zirconia to 50at.% alumina content, were deposited by reactive pulsed-DC magnetron sputtering using 51mm diameter Zr and Al targets. The coating had a Zr-Al-O solid solution structure that was composed of nano-size cubic-ZrO2 grains (20±5nm) with aluminum cations distributed inside them. The deposited coatings were annealed up to 1350°C and their structural changes were studied using Differential Scanning Calorimetry (DSC), X-ray diffraction (XRD), High Resolution Transmission Electron Microscopy (HRTEM) and Vickers hardness measurement. Two exothermic annealing events were observed. The first event appeared at 700–750°C and was contributed to aluminum segregation to the grain boundaries, and the formation of a nanocomposite-ZrO2/amorphous-Al2O3 structure. The second event appeared at 1000–1200°C and was related to coarsening (“Ostwald ripening”) of the ZrO2 grains. The coating hardness after the first event was stabilized to 19.5±1.1GPa because of the segregation, which hindered grain growth. However, after a second DSC cycle of the coating, only one sharp endothermic transformation peak was observed at onset temperature of 1060±5°C. This was associated with grain growth accompanied with zirconia transformation from the cubic to the monoclinic phase.

Alumina Growth and Interface Strengthening Mechanisms of Pt on the Surface of Bond Coats in EB-PVD TBC System Based on First-Principles

Oxygen adsorption, aluminium segregation and interface adhesion on the surface of NiPtAl and MCrAlY bond coats (BC) in EB-PVD TBC system were investigated using first-principles calculations within the density functional theory (DFT). Examination of oxygen adsorption and aluminium segregation indicated that the addition of Pt always obstructed the growth of alumina. In addition, NiPtAl, as bond coats in EB-PVD TBC System, had less lattice variation and stronger interface adhesion than MCrAlY when alumina was produced. It is found that Pt is an important factor that affects the Al2O3 growth in thermal barrier coating. It is proved that Pt improves the bonding performance of Al2O3 and lifetime of thermal barrier coating. This offsets the high cost of Pt in industry application.

Dendrite segregation in Ni3Al-based intermetallic single crystals alloyed with Cr, Mo, W, Ti, Co, and Re

The character of dendrite segregation in Ni3Al-based intermetallic VKNA-type alloy single crystals with a dendritic–cellular structure is studied. Distribution coefficient kd of an alloying element (AE) in the alloy during solidification kd = cd.a.I/c0 (c0 is the AE content in the alloy (liquid phase composition), cd.a.I is the AE content in primary dendrite arms of the alloy (in the solid phase)) and segregation coefficient ks = cd.a.I/ci.d (ci.d is the AE content in the interdendritic space) have been found. A comparative study of the dendrite segregation parameters in VKNA-nype Ni3Al-based intermetallic alloys and the well-known ZhS36-type nickel superalloy shows that the intermetallic alloys satisfy to the rule deduced for two- and three-component nickel-based superalloys: if an introduced AE increases the melting temperature of the basic metal, we have kd > 1 (Co, W, Re); if it decreases the melting temperature, we have kd < 1 (Al, Ti, Cr, Mo). Dendrite segregation coefficients ks are dependent on the proportion of the AE contents in the alloys. In nickel superalloys, the dendrite segregation of aluminum, tungsten, and rhenium is higher than that in the intermetallic alloys. The dendrite segregation coefficients of tungsten and rhenium is higher by a factor of 1.5–2 than that in the VKNA-type intermetallic alloys with a low content of refractory metals. This can be due to the retardation of diffusion of refractory metals in the solid phase of a nickel superalloy highly alloyed with these elements.

Effect of temperature on the initial stages of oxidation of γ-Al4Cu9(110)

Combined X-ray photoemission spectroscopy and low energy electron diffraction investigations have been performed to study the influence of temperature on the first stages of oxidation of the (110) surface of γ-Al4Cu9 complex metallic alloy in the pressure range 2–6×10−7mbar. The oxidation mechanism is driven by aluminium segregation. At 115K, a pure aluminium oxide film is formed, which does not present any long range order. CuO bonds are never observed. The lower oxidation kinetics compared to that previously observed at room temperature is due to blocking of the oxygen dissociation and/or a decrease in the aluminium segregation. However, aluminium segregation is still observed, even for this very low temperature, due to the low energy value of the activation energy for aluminium diffusion in γ-Al4Cu9 (0.65±0.12eV) which is related to the presence of two vacancies in the crystal structure. At 925K, fast aluminium segregation and possible oxygen diffusion into the bulk leads to the formation of domains or clusters of γ-like alumina either on top of or, more likely, below the surface.

Segregation and evaporation behaviors of aluminum and calcium in silicon during solidification process induced by electron beam

An experimental investigation into the removal of aluminum (Al) and calcium (Ca) from molten silicon by using electron beam melting was carried out. Based on the distributions of Al and Ca along the growth direction of the ingot under different solidification conditions, the influence of segregation and evaporation behaviors on the removal of such impurities with both high saturated vapor pressure and low segregation coefficients was investigated. The results showed that the distributions of impurities depend upon the interaction between segregation and evaporation, so that the removal efficiency can be further improved by adjusting the melting parameters. Compared with the traditional electron beam melting process, the energy consumption decreases by 20% during the whole melting and solidification process. It is considered to be a more effective way for the purification of silicon and the reduction of energy consumption by electron beam melting.

Three-dimensional structural analysis for crystal defects in phase-transformed Nb&amp;lt;sub&gt;3&amp;lt;/sub&gt;Al

The 3-D crystal structure of the planar defects formed in the Nb <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> Al phase via phase transformation was determined. The crystal defects are expected to be the effective pinning centers rather than grain boundaries in the transformation-processed Nb <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> Al conductors. The atomic arrangement of the Nb <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> Al phase was determined by high-angle annular dark-field scanning transmission electron microscopy (HAADF-STEM). The elemental analysis was performed by energy-dispersive X-ray spectroscopy (EDX). Plotting the atomic positions three-dimensionally considering the distance between the atoms, the 3-D structure of the crystal defect was determined. The planar defect was directly recognized to have the Zr <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">4</sub> Al <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> -type crystalline structure expanding on the {100} plane. The planar defects shift the Nb <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> Al crystalline phases across the defect plane by half a lattice parameter in the [100] direction. The thickness of the planar defect was 4.684 Å, whereas the lattice parameter of the A15 Nb <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sub> Al phase was 5.135 Å in HAADF-STEM images. HAADF-STEM, STEM-EDX, as well as 3-D atom probe tomography (APT) revealed that there was no aluminum segregation at grain boundaries, although Al segregation can be seen at planar defects. On the other hand, slight Ta segregation was detected by APT at the grain boundary in an examined specimen.

Growth and structure of ultrathin alumina films on the (1 1 0) surface of γ-Al4Cu9 complex metallic alloy

The first stages of oxidation of the (1 1 0) surface of a γ-Al4Cu9 complex metallic alloy were investigated by combining x-ray photoemission spectroscopy, low energy electron diffraction and scanning tunnel microscopy studies. Oxidation at room temperature in the 2 × 10−8 to 2 × 10−7 mbar oxygen pressure range occurs in two steps: a fast regime is followed by a much slower one, leading to the formation of a thin aluminium oxide film showing no long range order. Cu–O bonds are never observed, due to fast oxygen induced aluminium segregation. The low value of the estimated activation energy for aluminium diffusion (0.65 ± 0.12 eV at−1) was ascribed to the presence of two vacancies in the γ-Al4Cu9 structure. Annealing at 925 K the oxide film formed at room temperature leads to the formation of small crystallized domains with a sixton structure similar to structures reported in the literature following the oxidation of Cu-9% Al(1 1 1), NiAl (1 1 0) and FeAl(1 1 0) surfaces as well as ultrathin Al films deposited onto Cu(1 1 1) or Ni(1 1 1) surfaces. Two contributions were observed in the O1s peaks, which have been ascribed to loosely bound oxygen species and oxygen belonging to the sixton structure respectively.

Aluminum Segregation in ZA27 Rheocast Alloy

Aluminum segregation in zinc alloys is a well-known problem during melting and casting. In molten Zn alloys, in fact, Al tends to float on the surface of the bath because of its lower density than zinc. The same problem also occurs during casting solidification, causing chemical gradients along part thickness and soundness problems. As a consequence, the use of high aluminum content zinc alloys, such as ZA27, can be limited.In this paper the effectiveness of rheocasting method on decreasing Al-segregation phenomenon in ZA27 was investigated. The slurry was obtained by using the ultrasound technique, starting from the fully liquid down to different solid fraction percentages. The metal was then cast into a permanent steel mold. The produced samples were completely characterized by metallographic analysis (optical and scanning electron microscope), to assess the microstructure modification induced by the treatment. Hardness tests were also performed to evaluate mechanical properties. For comparison, the same tests were performed on conventionally cast samples.The analyses show that the use of a semisolid alloy increases the homogeneity of the part in terms of hardness, chemical composition and microstructure; furthermore casting’s shrinkage porosity is significantly reduced.

Yb:fiber laser surface texturing of stainless steel substrate, with MCrAlY deposition and CO2 laser treatment

Ceramic coatings are employed to avoid the oxidation effect on turbine blade metallic substrate and as well as, increase turbine work temperature, improving its performance on metallic substrates to increase their lifetime. A bond coat (BC) base of particulate material of Ni–Al powders is necessary to assure a good adherence and gradual decrease in thermal expansion coefficient between the blade metallic substrate and the ceramic top coating. This research aims to study the influence of the laser surface texturing on the deposition of particulate materials of MCrAlY (BC) on AISI 316L stainless steel substrate. The laser texturing was applied on the stainless steel surface by an Yb–fiber laser beam and further the BC powder was pre-deposited by a sedimentation technique and irradiated by a CO2 laser beam. Analyses of textured substrates and NiCrAlY coatings were carried out by different characterization techniques. These analyses showed that the LT was efficient to form a homogenous dense layer, without cracks or pronounced imperfections, leading to a metallurgical bonding between the substrate and the coating. The LST promoted the same metallurgical bond observed for LT. In addition, the coating showed higher thickness, aluminum segregation toward the surface and higher interdiffusion between the coating and underlying substrate elements.

Fabrication and microstructure of cerium doped lutetium aluminum garnet (Ce:LuAG) transparent ceramics by solid-state reaction method

Polycrystalline Ce3+ doped lutetium aluminum garnet (Ce:LuAG) transparent ceramics fabricated by one step solid-state reaction method using synthetic nano-sized Lu2O3, commercial α-Al2O3 and CeO2 powders were investigated in this paper. The green compacts shaped by the mixed powders were successfully densified into Ce:LuAG transparent ceramics after vacuum sintering at 1750°C for 10h. The in-line optical transmittance of the Ce:LuAG ceramic made by home-made Lu2O3 powders could reach 57.48% at 550nm, which was higher than that of the ceramic made by commercial Lu2O3 powders (22.96%). The microstructure observation showed that light scattering centers caused by micro-pores, aluminum segregation and refraction index inhomogeneities induced the decrease of optical transparency of the Ce:LuAG ceramics, which should be removed and optimized in the future work.

Solutioning and Aging of MAR-M247 Nickel-Based Superalloy

Despite the existence of previous studies on the heat treatment of the MAR-M247 superalloy, there is a lack of microstructural characterization data that support the heat-treatment conditions that are proposed in this study. Thus, the aim of this study is to investigate the changes in microstructure that occur in this alloy when subjected to different solutioning and aging heat treatments. Thermodynamic calculations and differential thermal analysis guided the experimental design and the analysis of experimental results. The MAR-M247 superalloy was produced via vacuum induction melting and investment casting. The samples were solutioned between 1185 and 1270 °C and aged between 770 and 980 °C. The as-cast and heat-treated samples were characterized using scanning electron microscopy in backscattered electron and secondary electron modes. Thermodynamic calculations have shown that the minimum solutioning temperature is approximately 1220 °C, occurring in a γ + MC + MB2 three-phase field (M = metal). The samples were solutioned at 1250 °C for 310 min before aging heat treatment. During solutioning the carbide composition is the MC phase shifts to higher hafnium (Hf) and lower tantalum (Ta) content, which is in agreement with the thermodynamics calculations. After solutioning, residual aluminum (Al) segregation leads to the formation of large γ′ particles in certain regions of the material following one-step aging heat treatment at 770 and 870 °C. However, a nearly uniform size distribution of γ′ particles was observed after aging at 980 °C as well as after double aging heat treatment at 980 °C for 300 min + 870 °C for 1200 min.