| 1. |
- Ashrafi, Hamid, et al.
(författare)
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Void formation and plastic deformation mechanism of a cold-rolled dual-phase steel during tension
- 2020
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Ingår i: Acta Metallurgica Sinica (English Letters). - : Springer. - 1006-7191 .- 2194-1289. ; 33, s. 299-306
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Tidskriftsartikel (refereegranskat)abstract
- The void formation and plastic deformation micromechanisms of a cold-rolled DP600 steel during tensile loading were studied by scanning electron microscopy (SEM) and electron backscatter diffraction (EBSD). The SEM observations revealed that the main void nucleation mechanism in the DP600 steel is decohesion at the ferrite–martensite interfaces. The voids were mostly observed between the closely spaced martensite islands situated at the boundaries of relatively finer ferrite grains. The EBSD results indicated a strain gradient developed from the ferrite–martensite and ferrite–ferrite interfaces into the interior of ferrite grains during the tensile deformation, which led to a stress concentration at these interfaces. Moreover, it was demonstrated that local misorientation inside the finer ferrite grains surrounded by martensite islands was higher than that for the coarser ferrite grains, which made the former more prone to void initiation.
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| 2. |
- Bogdanoff, Toni, et al.
(författare)
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The influence of copper addition on crack initiation and propagation in an Al–Si–Mg alloy during cyclic testing
- 2020
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Ingår i: Materialia. - : Elsevier. - 2589-1529. ; 12
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Tidskriftsartikel (refereegranskat)abstract
- The effect of copper (Cu) addition up to 3.2 wt% on crack initiation and propagation in an Al–Si–Mg cast alloy was investigated using in-situ cyclic testing in the as-cast condition. A combination of digital image correlation, electron backscatter diffraction, and scanning electron microscopy was used to investigate crack initiation and propagation behaviour during in-situ cyclic testing. The results showed that Cu-rich intermetallic compounds with the addition of Cu up to 1.5 wt% do not affect the fatigue behaviour of these alloys, and that crack propagation in these cases is trans-granular and trans-dendritic. However, increasing the concentration of the Cu retained in the primary α-Al matrix in solid solution and Cu-containing precipitates delayed crack propagation during cyclic testing. The results showed that strain accumulation was highest at the grain boundaries; however, the crack preferred to propagate along or across primary α-Al dendrites due to the relatively lower mechanical strength of the matrix compared to the eutectic and intermetallic phases. Moreover, the addition of Cu of more than 3.0 wt% to Al-Si-Mg alloys changes the fatigue behaviour that a rapid failure occurs.
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| 3. |
- Hernando, Juan Carlos, et al.
(författare)
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The role of primary austenite morphology in hypoeutectic compacted graphite iron alloys
- 2020
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Ingår i: International Journal of metalcasting. - : Springer. - 1939-5981 .- 2163-3193. ; 14:3, s. 745-754
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Tidskriftsartikel (refereegranskat)abstract
- This work investigates the role of primary austenite morphology on the eutectic and eutectoid microstructures and the ultimate tensile strength (UTS) in a hypoeutectic compacted graphite iron (CGI) alloy. The morphology of primary austenite is modified by isothermal coarsening experiments in which holding times up to 60 min are applied to the solid–liquid region after coherency. The cooling conditions for the subsequent eutectic and eutectoid reactions are similar. Miniaturized tensile tests are performed to evaluate the UTS. The morphological characteristics related to the surface area of primary austenite, the modulus of primary austenite, Mγ, and the hydraulic diameter of the interdendritic region, DHydID, increase with the cube root of coarsening time. The eutectic and eutectoid microstructures are not significantly affected by the morphology of primary austenite, thus indicating that the morphology of the interdendritic regions does not control the nucleation frequency and growth of eutectic cells or graphite. UTS decreases linearly with the increasing coarseness of primary austenite for similar eutectic and eutectoid microstructures, demonstrating the strong influence of primary austenite morphology on the UTS in hypoeutectic CGI alloys.
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| 4. |
- Mazaheri, Y., et al.
(författare)
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On the simultaneous improving of strength and elongation in dual phase steels via cold rolling
- 2020
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Ingår i: Metals. - : MDPI. - 2075-4701. ; 10:12, s. 1-16
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Tidskriftsartikel (refereegranskat)abstract
- The ferrite-pearlite microstructure was cold-rolled to form dual phase (DP) steels, the percentage reduction of which varied. To do so, the steels were annealed in two steps and then the workpiece underwent water quenching. Accordingly, a decrease was observed in the average size of the ferrite grains, from above 15 µm to below 2 µm, subsequent to the thermomechanical processing. By an increase in the reduction percentage, the volume fraction of martensite grew. The balance between strength and elongation also improved nearly 3 times, equivalent to approximately 37,297 MPa% in DP in comparison to 11,501 MPa% in the ferrite-pearlite microstructure, even after 50% cold-rolling. Based on Hollomon and differential Crussard-Jaoul (DC–J) analyses, the DP steels under investigation deformed in two and three stages, respectively. The modified C–J (MC–J) analysis, however, revealed that the deformation process took place in four stages. The rate of strain hardening at the onset of the deformation process was rather high in all DP steels. The given rate increased once the size of the ferrite grains reduced; an increase in the volume fraction of martensite due to larger percentage of reduction also contributed to the higher rate of strain hardening. The observation of the fractured surfaces of the tensile specimens indicated ductile fracture of the studied DP steels.
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| 5. |
- Sainis, Salil, et al.
(författare)
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The influence of size and nearest neighbour distance of intermetallic particles in cast Al-Si alloys on the localized deposition of cerium conversion coatings
- 2020
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Konferensbidrag (refereegranskat)abstract
- Corrosion inhibiting cerium conversion coatings (CeCC) reduce corrosion by preferentially forming cerium rich deposits onto cathodic sites and thereby reducing their electrochemical activity upon immersion in cerium containing baths. The spontaneous and localized deposition of CeCCs, which is driven by the local rise in pH on cathodic sites as a result of oxygen reduction reaction, occurs by the combination of OH - and Ce 3+ ions, forming an insoluble precipitate of cerium oxides and/or hydroxides. The rate of pH rise has been previously reported to be governed by; the cathodic activity of intermetallic particles (IM). Nevertheless, the role of the substrate’s microstructure on CeCC deposition behaviour, specifically the influence of different IMs’ size and nearest-neighbor-distance on the deposition, has not been studied in detail. This paper aims to shed some light on the mentioned gap by depositing cerium-conversion coatings, on two microstructures each containing IMs with relatively different nobilities - (a) more noble Cu-rich θ-Al2Cu (b) Fe-rich IM β-Al5FeSi with different sizes and spatial distribution. Model alloy composition of Al-7wt.%Si-2wt.%Cu-1wt.%Fe was solidified at different cooling rates, allowing formation of the two different microstructures that consists of (1) β and θ IMs of large size (10-143 µm) with relatively larger nearest-neighbor distance and (2) β and θ of small size (2-23 µm) with relatively closer nearest-neighbor distance. Uncoated alloy and CeCC deposited microstructure as well as associated local and global electrochemical properties, were characterized with optical microscopy, scanning electron microscopy, energy-dispersive X-ray spectroscopy, atomic force microscopy, scanning Kelvin probe force microscopy and potentiodynamic polarization techniques.
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| 6. |
- Sainis, Salil, et al.
(författare)
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The role of microstructure and cathodic intermetallics in localised deposition mechanism of conversion compounds on Al (Si, Fe, Cu) alloy
- 2020
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Ingår i: Surface & Coatings Technology. - : Elsevier. - 0257-8972 .- 1879-3347. ; 402
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Tidskriftsartikel (refereegranskat)abstract
- Cerium-based conversion coating formation is triggered by a local rise in pH at cathodic sites produced by the oxygen reduction reaction. Therefore, size, morphology distribution and electrochemical potential of those sites play a crucial role. While the deposition reaction is sensitive to both immersion bath concentrations and underlying substrate microstructure, only the former has been widely investigated. This research attempts to fill the gap by studying the effect of controlled microstructure variables like the cathodic intermetallics' geometry and spatial distribution on the conversion compound deposit initiation. A controlled cast Al alloy was synthesised for this study and consisted of distinct cathodic phases: Cu-rich intermetallics, Fe-rich intermetallics and Si particles. The localised deposition preferentially formed only on strong cathodic Cu-rich intermetallics. Size (surface area) of the Cu-rich intermetallic correlated linearly with the deposited area over it in terms of lateral and z-direction spread. The pH gradient occurring from the oxygen reduction near an IM is very local and does not affect pH gradients of a neighbouring IM. When immersion time is increased from 0.5 h to 1 h, the percentage of Cu-rich IM covered with conversion coating increases. Big Cu-rich IM activate faster for deposition reaction than small Cu-rich IM.
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| 7. |
- Sreekanth, Suhas, et al.
(författare)
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Effect of Direct Energy Deposition Process Parameters on Single-Track Deposits of Alloy 718
- 2020
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Ingår i: Metals. - : MDPI AG. - 2075-4701. ; 10:1, s. 01-16
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Tidskriftsartikel (refereegranskat)abstract
- The effect of three important process parameters, namely laser power, scanning speed and laser stand-off distance on the deposit geometry, microstructure and segregation characteristics in direct energy deposited alloy 718 specimens has been studied. Laser power and laser stand-off distance were found to notably affect the width and depth of the deposit, while the scanning speed influenced the deposit height. An increase in specific energy conditions (between 0.5 J/mm2 and 1.0 J/mm2) increased the total area of deposit yielding varied grain morphologies and precipitation behaviors which were comprehensively analyzed. A deposit comprising three distinct zones, namely the top, middle and bottom regions, categorized based on the distinct microstructural features formed on account of variation in local solidification conditions. Nb-rich eutectics preferentially segregated in the top region of the deposit (5.4–9.6% area fraction, Af) which predominantly consisted of an equiaxed grain structure, as compared to the middle (1.5–5.7% Af) and the bottom regions (2.6–4.5% Af), where columnar dendritic morphology was observed. High scan speed was more effective in reducing the area fraction of Nb-rich phases in the top and middle regions of the deposit. The <100> crystallographic direction was observed to be the preferred growth direction of columnar grains while equiaxed grains had a random orientation.
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| 8. |
- Zamani, Mohammadreza, 1985-, et al.
(författare)
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Study on dissolution of Al2Cu in al-4.3cu and a205 cast alloys
- 2020
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Ingår i: Metals. - : MDPI AG. - 2075-4701. ; 10:7
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Tidskriftsartikel (refereegranskat)abstract
- Evolution of microstructure in a binary Al-Cu system (Al-4.3Cu) and a commercially alloyed Al-Cu system (A205) during solution heat treatment was investigated using optical microscopy (OM), scanning electron microscopy (SEM), wavelength-dispersive X-ray spectroscopy (WDS), and differential scanning calorimetry (DSC). The diversified coarseness of the microstructure was initiated by controlling the solidification rate. Different solution treatment temperatures were applied to identify a proper solutioning temperature. The larger microstructural scale required an increased solutioning temperature and prolonged holding time to obtain homogenized solutes in the α-Al matrix. The diffusion of Cu primarily controlled the solution heat treatment process. A diffusion-based model was applied and calibrated to determine the dissolution rate of an Al2Cu particle in the matrix. The model operates on a similar time scale with the experimental results for the Al-4.3Cu and A205 alloys with various microstructural scales, different chemical compositions, and at different solution treatment temperatures. Three-dimensional (3D) reconstructed images from SEM images and energy dispersive spectroscopy (EDS) map of elements showed that TiB2 particles shield the Cu-rich phases in the boundaries of α-Al grains, presumably acting as a physical barrier to the diffusion of Cu solutes toward α-Al grains. The model also suggests that the effective diffusion coefficient of Cu in Al, in the presence of TiB2 particles, reduced by a factor of 2.0–2.5 in the A205 alloy compared with the binary Al-Cu alloy. © 2020 by the authors.
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