| 1. |
- Apaydin, R. O., et al.
(författare)
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Single-Step Production of Nanostructured Copper-Nickel (CuNi) and Copper-Nickel-Indium (CuNiIn) Alloy Particles
- 2016
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Ingår i: Metallurgical and Materials Transactions A: Physical Metallurgy and Materials Science. - : Springer Science and Business Media LLC. - 1073-5623. ; 47A:7, s. 3744-3752
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Tidskriftsartikel (refereegranskat)abstract
- Nanostructured copper-nickel (CuNi) and copper-nickel-indium (CuNiIn) alloy particles were produced from aqueous solutions of copper, nickel nitrates and indium sulfate by hydrogen reduction-assisted ultrasonic spray pyrolysis. The effects of reduction temperatures, at 973 K, 1073 K, and 1173 K (700 A degrees C, 800 A degrees C, and 900 A degrees C), on the morphology and crystalline structure of the alloy particles were investigated under the conditions of 0.1 M total precursor concentration and 0.5 L/min H-2 volumetric flow rate. X-ray diffraction studies were performed to investigate the crystalline structure. Particle size and morphology were investigated by scanning electron microscope and energy-dispersive spectroscopy was applied to determine the chemical composition of the particles. Spherical nanocrystalline binary CuNi alloy particles were prepared in the particle size range from 74 to 455 nm, while ternary CuNiIn alloy particles were obtained in the particle size range from 80 to 570 nm at different precursor solution concentrations and reduction temperatures. Theoretical and experimental chemical compositions of all the particles are nearly the same. Results reveal that the precursor solution and reduction temperature strongly influence the particle size of the produced alloy particles.
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| 2. |
- Asala, G., et al.
(författare)
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Microstructural Analyses of ATI 718Plus® Produced by Wire-ARC Additive Manufacturing Process
- 2017
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Ingår i: Metallurgical and Materials Transactions. A. - : Springer Science and Business Media LLC. - 1073-5623 .- 1543-1940. ; 48A:9, s. 4211-4228
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Tidskriftsartikel (refereegranskat)abstract
- A detailed microstructural study of ATI 718Plus superalloy produced by the wire-arc additive manufacturing (WAAM) process was performed through the use of scanning electron microscopy (SEM), transmission electron microscopy (TEM), electron probe micro-analysis (EPMA), and electron backscatter diffraction (EBSD). Extensive formation of eutectic solidification microconstituents including Laves and MC-type carbide phases, induced by micro-segregation, are observed in the build of the alloy in the as-deposited condition. Notwithstanding the significant segregation of niobium (Nb), which has been reported to promote the formation of the delta-phase in ATI 718Plus, only eta-phase particles are observed in the deposit. Excessive precipitation of eta-phase particles is found to be linked to Laves phase particles that are partially dissolved in the deposit after post-deposition heat treatment (PDHT). The EBSD analysis shows a high textured build in the aOE (c) 100 > directions with only a few misoriented grains at the substrate-deposit boundary and the top of the deposit. Investigation on the hardness of the build of the alloy, in the as-deposited condition, showed a softened zone about 2 mm wide at the deposited metal heat affected zone (DMHAZ), which has not been previously reported and potentially damaging to the mechanical properties. An extensive analysis with the use of both microstructural characterization tools and theoretical calculations shows that the DMHAZ has the lowest volume fraction of strengthening precipitates (gamma’ and gamma aEuro(3)) in terms of their number density, which therefore induces the observed softness. Delayed re-precipitation kinetics and the extent of the precipitation of gamma’ and gamma aEuro(3) in the DMHAZ which is related to the diffusion of segregated solute elements from the interdendritic regions are attributed to this phenomenon. The microstructural analyses discussed in this work are vital to adequate understanding of properties of ATI 718Plus produced by the additive manufacturing process technique.
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| 3. |
- Bayat, Nazlin, et al.
(författare)
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Influence of Heat Treatment on the Surface Structure of 6082 Al Alloys
- 2017
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Ingår i: Metallurgical and Materials Transactions. A. - : Springer Science and Business Media LLC. - 1073-5623 .- 1543-1940. ; 48A:10, s. 5085-5094
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Tidskriftsartikel (övrigt vetenskapligt/konstnärligt)abstract
- The β-Al5FeSi intermetallic phase and coarse Mg2Si particles have negative effects on extrudability and workability of 6xxx Al alloys billets. To achieve extruded products with a high surface quality, the as-cast billets are heat-treated before extrusion. During heat treatment, the undesired intermetallic particles, i.e., β-AlFeSi platelets are transformed to rounded α-Al(FeMn)Si intermetallic phases. Although the heat treatment of the bulk areas of the 6xxx Al alloys has been the focus of many previous studies, the process of phase transformation at the very surface has not been paid the same attention. In this study, microstructures of a homogenized billet of a 6082 alloy at the area very close to the surface were investigated. By comparing the X-ray diffraction patterns (XRD) of heat-treated samples as a function of different holding times, the gradual phase transformations could be followed, and using GDOES and map analysis by EDX, the alloying elemental redistribution was analyzed. Partial remelting and porosity growth was detected, and transformation rates were faster than in bulk material and from what is known from industrial processes.
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| 4. |
- Cai, Xiaoping, et al.
(författare)
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Oxidation Resistance of Highly Porous Fe-Al Foams Prepared by Thermal Explosion
- 2018
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Ingår i: Metallurgical and Materials Transactions. A. - : Springer. - 1073-5623 .- 1543-1940. ; 49A:8, s. 3683-3691
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Tidskriftsartikel (refereegranskat)abstract
- Open-cell Fe-Al intermetallic foams were successfully prepared by a simple and energy-saving thermal explosion (TE) process. The effects of the Fe/Al molar ratio (Fe-(40–50) at. pct Al) and thermal treatment temperature on the TE temperature profile, phase composition, pore characteristics, and oxidation resistance of the prepared foams were investigated. The results showed that the Al content significantly influenced the ignition (Tig) and combustion (Tc) temperatures of the TE process; in particular, as the Al content decreased, Tig increased gradually from 623 °C to 636 °C and Tc decreased from 1059 °C to 981 °C. FeAl was identified as the dominant phase in the thermally treated foams. The Fe-Al intermetallic foams displayed an open porosity of 60 vol pct, with pores connected with each other to form an open pore structure. The formation of the pores was attributed to the expansion of interparticle pores in the pressed body during the TE reaction. X-ray photoelectron spectroscopy analysis of the Fe-50Al foam showed that the Al 2p and O 1s binding energies were 74.5 eV and at 531.4 eV, respectively. The formation of a surface alumina layer in the early stages of the oxidation process resulted in the parabolic oxidation rate law, and the Fe-50Al foams exhibited an excellent resistance to oxidation at 650 °C in air. These results suggest that the synthesized Fe-Al foams represent promising materials for applications involving an oxidizing environment and high temperatures.
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| 5. |
- Calmunger, Mattias, et al.
(författare)
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Characterization of austenitic stainless steels deformed at elevated temperature
- 2017
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Ingår i: Metallurgical and Materials Transactions. A. - : Springer-Verlag New York. - 1073-5623 .- 1543-1940. ; 48A:10, s. 4525-4538
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Tidskriftsartikel (refereegranskat)abstract
- Highly alloyed austenitic stainless steels are promising candidates to replace more expansive nickel-based alloys within the energy-producing industry. The present study investigates the deformation mechanisms by microstructural characterisation, mechanical properties and stress-strain response of three commercial austenitic stainless steels and two commercial nickel-based alloys using uniaxial tensile tests at elevated temperatures from 400 C up to 700 C. The materials showed different influence of temperature on ductility, where the ductility at elevated temperatures increased with increasing nickel and solid solution hardening element content. The investigated materials showed planar dislocation driven deformation at elevated temperature. Scanning electron microscopy showed that deformation twins were an active deformation mechanism in austenitic stainless steels during tensile deformation at elevated temperatures up to 700 C.
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| 6. |
- Casellas, Daniel, et al.
(författare)
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Fracture Toughness to Understand Stretch-Flangeability and Edge Cracking Resistance in AHSS
- 2017
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Ingår i: Metallurgical and Materials Transactions. A. - : Springer. - 1073-5623 .- 1543-1940. ; 48A:1, s. 86-94
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Tidskriftsartikel (refereegranskat)abstract
- The edge fracture is considered as a high risk for automotive parts, especially for parts made of advanced high strength steels (AHSS). The limited ductility of AHSS makes them more sensitive to the edge damage. The traditional approaches, such as those based on ductility measurements or forming limit diagrams, are unable to predict this type of fractures. Thus, stretch-flangeability has become an important formability parameter in addition to tensile and formability properties. The damage induced in sheared edges in AHSS parts affects stretch-flangeability, because the generated microcracks propagate from the edge. Accordingly, a fracture mechanics approach may be followed to characterize the crack propagation resistance. With this aim, this work addresses the applicability of fracture toughness as a tool to understand crack-related problems, as stretch-flangeability and edge cracking, in different AHSS grades. Fracture toughness was determined by following the essential work of fracture methodology and stretch-flangeability was characterized by means of hole expansions tests. Results show a good correlation between stretch-flangeability and fracture toughness. It allows postulating fracture toughness, measured by the essential work of fracture methodology, as a key material property to rationalize crack propagation phenomena in AHSS.
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| 7. |
- Chen, Zhe, et al.
(författare)
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Surface Integrity and Structural Stability of Broached Inconel 718 at High Temperatures
- 2016
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Ingår i: Metallurgical and Materials Transactions. A. - : Springer. - 1073-5623 .- 1543-1940. ; 47A:7, s. 3664-3676
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Tidskriftsartikel (refereegranskat)abstract
- The current study focused on the surface integrity issues associated with broaching of Inconel 718 and the structural stability of the broached specimen at high temperatures, mainly involving the microstructural changes and residual stress relaxation. The broaching operation was performed using similar cutting conditions as that used in turbo machinery industries for machining fir-tree root fixings on turbine disks. Thermal exposure was conducted at 723 K, 823 K, and 923 K (450 A degrees C, 550 A degrees C, and 650 A degrees C) for 30, 300, and 3000 hours, respectively. Surface cavities and debris dragging, sub-surface cracks, high intensity of plastic deformation, as well as the generation of tensile residual stresses were identified to be the main issues in surface integrity for the broached Inconel 718. When a subsequent heating was applied, surface recrystallization and alpha-Cr precipitation occurred beneath the broached surface depending on the applied temperature and exposure time. The plastic deformation induced by the broaching is responsible for these microstructural changes. The surface tension was completely relaxed in a short time at the temperature where surface recrystallization occurred. The tensile layer on the sub-surface, however, exhibited a much higher resistance to the stress relief annealing. Oxidation is inevitable at high temperatures. The study found that the surface recrystallization could promote the local Cr diffusion on the broached surface.
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| 8. |
- De Oro Calderón, Raquel, 1982, et al.
(författare)
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New Alloying Systems for Sintered Steels: Critical Aspects of Sintering Behavior
- 2015
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Ingår i: Metallurgical and Materials Transactions A: Physical Metallurgy and Materials Science. - : Springer Science and Business Media LLC. - 1073-5623. ; 46:3, s. 1349-1359
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Tidskriftsartikel (refereegranskat)abstract
- Oxygen-sensitive alloying elements such as Mn, Si, and Cr have a high potential for improving the properties of low alloyed sintered steels while reducing the alloying cost. However, it is necessary to find a way for avoiding, or at least minimizing, the oxidation of these elements especially during the early stages of the sintering cycle. In this study Mn, Si, and Cr were introduced in the form of a master alloy powder designed to be mixed with the iron base powder and provide the final composition of the steel during the sintering process. The reduction/oxidation phenomena taking place during the heating stage were studied by thermogravimetry, dilatometry, and mass spectroscopy, using either reducing (H2) or inert (Ar) atmospheres. The results show how the difference in chemical activity between base iron powder and master alloy causes the so called “internal-getter” effect, by which the reduction of less stable iron oxides leads to oxidation of the elements with higher affinity for oxygen. This effect can be somehow minimized when sintering in H2, since the iron oxides are reduced at lower temperatures at which the reactivity of the elements in the master alloy is lower. However, H2 concentration in the processing atmosphere needs to be carefully adapted to the specific composition of the materials being processed in order to minimize decarburization by methane formation during sintering.
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| 9. |
- Esfahani, Hosein Bartar, et al.
(författare)
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The Effect of Strontium on the Strength of Layers of Double Oxide Film Defects
- 2016
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Ingår i: Metallurgical and Materials Transactions. A. - : Springer. - 1073-5623 .- 1543-1940. ; 47A:3, s. 1331-1338
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Tidskriftsartikel (refereegranskat)abstract
- The change in the strength of layers of oxide film (bifilm) defects when held in Al-0.05 and 0.1 wt pct melts was evaluated indirectly by comparing the porosity, average pore roundness, and pore number density results obtained from a reduced pressure test of the commercial purity and Sr-containing Al melts subjected to different holding and vibration regimes. Any changes in the composition of the pores were also studied using scanning electron microscopy and energy-dispersive X-ray spectroscopy. The results showed that the Al2O3 layers of a newly formed oxide film defect, when held in Al-0.05 or 0.1 wt pct Sr melt, transformed gradually into an Sr-containing oxide. This transformation caused the strength of the oxide layers to increase and the rate of the expansion of its atmosphere and removal of the defect from the melt to decrease. This might influence the increase in the porosity of Sr-modified Al castings.
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| 10. |
- Ferraro, Stefano, et al.
(författare)
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On the formation of sludge intermetallic particles in secondary aluminum alloys
- 2015
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Ingår i: Metallurgical and Materials Transactions. A. - : Springer. - 1073-5623 .- 1543-1940. ; 46:8, s. 3713-3722
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Tidskriftsartikel (refereegranskat)abstract
- The primary precipitation of Fe-rich intermetallics in AlSi9Cu3(Fe) type alloys is studied for different Fe, Mn, and Cr contents and cooling rates. Differential scanning calorimetry, thermal analysis, and interrupted solidification with a rapid quenching technique were used in combination in order to assess the nucleation temperature of sludge particles, as well as to follow their evolution. The results revealed that the sludge nucleation temperature and the release of latent heat during sludge formation are functions of Fe, Mn, and Cr levels in the molten alloy (i.e., the sludge factor, SF) and cooling rate. Moreover, it can be concluded that sensitivity to sludge formation is not affected by cooling rate; i.e., a decrease in the SF will reduce sludge nucleation temperature to the same extent for a higher cooling rate as for a lower cooling rate. The sludge formation temperature detected will assist foundries in setting the optimal molten metal temperature for preventing sludge formation in holding furnaces and plunger systems.
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