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Sökning: hsv:(TEKNIK OCH TEKNOLOGIER) hsv:(Materialteknik) hsv:(Metallurgi och metalliska material)

  • Resultat 4151-4160 av 5725
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4151.
  • Qiu, Ren, 1993, et al. (författare)
  • CVD TiAlN coatings with tunable nanolamella architectures
  • 2021
  • Ingår i: Surface and Coatings Technology. - : Elsevier BV. - 0257-8972. ; 413
  • Tidskriftsartikel (refereegranskat)abstract
    • In this work, Ti1-xAlxN (TiAlN) coatings were synthesized by low pressure chemical vapour deposition (LPCVD), and the influence of a rotational precursor gas supply on the coating microstructure was studied. The microstructure of the TiAlN coatings were characterized using X-ray diffraction (XRD), scanning and transmission electron microscopy (SEM and TEM), and electron backscattered diffraction (EBSD). It is shown that a rotational precursor gas supply induces an oscillatory surface reaction, which causes a nanolamella architecture. When the gas beam directly hits the sample, the local gas flow velocity is high, which increases the deposition rate of Ti and a Ti(Al)N lamella is formed. When the gas beam rotates away, the local gas velocity is low, so the deposition rate of Ti decreases, and an Al(Ti)N lamella is formed. As this is repeated a periodic nanolamella architecture is formed. The nanolamellae grow epitaxially on three {001} facets of the 111 textured grains, which leads to a pyramidal surface morphology. Without gas supply rotation, a high Al content cubic phase was still obtained, but no nanolamella was formed. This indicates that Ti-rich lamellae are not necessary to stabilize an Al-rich cubic TiAlN phase. In addition, spinodal decomposition is not likely to be the driving force behind the nanolamella formation in LPCVD TiAlN, as this would also have happened in the sample without a rotational gas supply. Finally, the nanolamella periodicity is found to be tunable via controlling the rotation speed of the precursor supply relative to the coating growth rate.
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4152.
  • Que, Zaiqing, et al. (författare)
  • Brittle fracture initiation in decommissioned boiling water reactor pressure vessel head weld
  • 2022
  • Ingår i: Journal of Nuclear Materials. - : Elsevier BV. - 0022-3115 .- 1873-4820. ; 569
  • Tidskriftsartikel (refereegranskat)abstract
    • The brittle fracture initiation behavior and fracture toughness in the ductile-to-brittle transition region for a thermally-aged weld metal of a decommissioned reactor pressure vessel head (in operation at 288 degrees C for 23 effective full power years) and in the non-aged reference condition were investigated. The results show that brittle fracture initiated primarily from non-metallic inclusions. The correlation between frac-ture toughness and brittle fracture initiation type (inclusion debonding or breakage), initiator size, initi-ation location (as-welded or re-heated regions in the weld metal) were analysed. Despite that thermal ageing does not affect significantly the fracture toughness, it could promote the debonding as a brit-tle fracture primary initiation type. The influence of debonded inclusion on the evolution of cumulative damage and brittle fracture initiation was assessed using crystal plasticity modelling.
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4153.
  • Queirós, Ricardo, et al. (författare)
  • Unraveling compacted and nodular cast iron porosity : Case studies approach
  • 2023
  • Ingår i: International Journal of metalcasting. - : Springer. - 1939-5981 .- 2163-3193.
  • Tidskriftsartikel (refereegranskat)abstract
    • Porosity is the culprit for a large fraction of scrap in cast iron foundries, resulting in significant environmental and productivity losses. The present work focuses on characterizing and explaining porosity defects in industrial compacted and nodular graphite cast iron components, utilizing current literature for reference. The goal is to identify existing knowledge gaps in the field, fostering further research work. Complex-shaped castings were sampled from three foundries, weighing between 100 and 300 kg. These were carefully selected to capture recurring defects during stable production. The mechanisms behind these defects were discussed, and the findings were compared to the literature. Scanning electron microscopy (SEM) was used to investigate the inner surfaces of the pores with secondary electron imaging. The surrounding microstructure was captured with optical microscopy in combination with image analysis, where panoramic images and nodularity maps were built. Ultimately, etching based on Si segregation was employed. The results suggest that the understanding of pore surface film formation remains limited, particularly regarding graphite film formation. Notably, the observations reveal a multitude of previously unreported graphite structures within the pores, some with particles in their centers containing Ce, Ca, La and S. These novel structures can provide additional insights regarding pore formation chronology.
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4154.
  • Radhakrishnan, M, et al. (författare)
  • Effect of chromium variation on evolution of magnetic properties in laser direct energy additively processed CoCrxFeNi alloys
  • 2023
  • Ingår i: Scripta Materialia. - : Elsevier BV. - 1359-6462. ; 226
  • Tidskriftsartikel (refereegranskat)abstract
    • The soft magnetic behavior of laser directed energy deposited CoCrxFeNi (x = 0 - 24 at.% Cr) alloys has been investigated as a function of chromium content. The saturation magnetization of these CoCrxFeNi alloys monotonically decreased with increasing concentration of Cr, and exhibited paramagnetic behavior at room temperature for equiatomic CoCrFeNi alloy composition. Similarly, the Curie temperature (Tc) of the ferromagnetic CoFeNi alloy linearly decreased with Cr content, while the paramagnetic equiatomic alloy indicated a ferromagnetic transition temperature of 94 K. Interestingly, all the as-deposited alloys exhibited coercivity values less than 2 Oe irrespective of the Cr content. The results indicate that the magnetic behavior of the ferromagnetic CoFeNi alloy can be systematically tuned with addition of antiferromagnetic Cr, and the additive manufacturing route was successful in rapid processing alloys of any desired composition, in a high throughput manner, with negligible chemical variation. These findings are promising for the fabrication of components for applications demanding gradient magnetic coatings and alloys.
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4155.
  • Ragnarsson, Lars, 1981-, et al. (författare)
  • Erosion of runners in ingot casting
  • 2009
  • Ingår i: AISTech - Iron and Steel Technology Conference Proceedings. ; , s. 1077-1087
  • Konferensbidrag (refereegranskat)abstract
    • Substantial erosion of the runner, especially the horizontal runner was noticed during casting. CFD simulation of the flow showed that the velocities were almost zero close to the centre stone and end stone. The low velocities well explained the minor erosion of the two types of stones. The CFD calculation also indicated that the velocities in the horizontal were not evenly distributed. Velocities as high as 3 m/s could be found at the entrance of the horizontal runner and close to the entrance of the ingot. This result was in good agreement with the experimental observation that the erosion close to the entrance of the horizontal runner was much more profound. The runner surface was found to react with the dissolved aluminium forming a layer of higher alumina content. The zigzag surface of the refractory could entrap inclusions and provide good condition for agglomeration. The detachment of the agglomerated inclusions along with the pieces of refractory could be an important source of the formation of macro inclusions during casting. The higher alumina contents in the inclusions found in the steel rod in comparison with that found in the ladle suggested possible reoxidation of the steel during casting.
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4156.
  • Ragnarsson, Lars, et al. (författare)
  • Flow pattern in ingot during mould filling and its impact on inclusion removal
  • 2010
  • Ingår i: Ironmaking & steelmaking. - 0301-9233 .- 1743-2812. ; 37:5, s. 347-352
  • Tidskriftsartikel (refereegranskat)abstract
    • A two-dimensional non-steady state computational fluid dynamic model was employed to gain a basic understanding of the flow in the ingot during casting. The surface velocity was found to be affected by the inlet angle and was found to vary with the casting level. The information of surface velocity was related to the probability of the inclusion removal. Water model experiments were also conducted to help the understanding. The model calculation revealed the same trends as the results of water model experiments. Both computational fluid dynamic data and the physical modelling showed that the inlet angle of 5 degrees currently used in the industry was a good alternative regarding inclusion removal. The present work suggests strongly that the melting shop should try to obtain a liquid or semiliquid film at as early stage as possible in ingot casting.
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4157.
  • Ragnarsson, Lars, 1981- (författare)
  • Formation of non-metallic inclusions and the possibility of their removal during ingot casting
  • 2010
  • Doktorsavhandling (övrigt vetenskapligt/konstnärligt)abstract
    • The present study was carried out to investigate the formation and evolution of non-metallic inclusions during ingot casting. Emphasize have been on understanding the types of inclusions formed and developed through the casting process and on the development of already existing inclusions carried over from the ladle during casting. Industrial experiments carried on at Uddeholm Tooling together with laboratory work and Computational Fluid Dynamics (CFD) simulations. Ingots of 5.8 tons have been sampled and the types of inclusions together with their distribution within the ingot have been characterized. Two new types of inclusions have been found. Type C1 is found originated from casting powder and in the size from a few μm to 30 μm. Type C2 is of macro inclusion type sizing up to 70 μm. The presence of C2 inclusions are few but very detrimental for the quality of the steel. Both types, C1 and C2 consist of alumina, indicating that reoxidation is the main reason for their existence. The protecting argon shroud has been studied by the use of a 1:1 scaled 2D model. Both flow pattern and oxygen measurement have been carried out. CFD has also been used as an auxiliary tool. It has been found that the oxygen pickup through argon gas shroud depends mostly on the distance between the ladle and the collar placed on top of runner. Further increase of gas flow rate above 2.5 m3.h-1 had very little effect on the oxygen distribution since both the flushing effect and the entraining effect with respect to oxygen are enhanced by further increase of inert gas flow rate. In the case of dual gas inlet, the flow in the shroud was found much less diffused compared with either vertical or horizontal injection system. The oxygen content in this arrangement was also greatly reduced. Studies of the runner after casting revealed a sparse non-metallic network structure around the periphery of the steel rod remained in the runner. The surface of the refractory had been severely attacked by the mechanical force from the streaming steel. The erosions of the centre stone and the end stone were on the other hand negligible. CFD calculations showed that the flow at those locations is almost stagnant. The surface of the refractory in contact with the steel was found to have an increased content of alumina. The source for the alumina could come from either exchange reaction of dissolved aluminium replaces the silica or reoxidation products origin from oxygen pick up during the transfer from the ladle to the vertical runner. Inclusions were also found entrapped in the steel refractory interface. It was also found that a formation of a liquid slag film as early as possible during casting would increase the possibility to remove inclusions and especially inclusions generated by the casting powder.
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4158.
  • Ragnarsson, Lars, et al. (författare)
  • Inclusions Generated during Ingot Casting of Tool Steel
  • 2010
  • Ingår i: STEEL RESEARCH INTERNATIONAL. - : Wiley. - 1611-3683 .- 1869-344X. ; 81:1, s. 40-47
  • Tidskriftsartikel (refereegranskat)abstract
    • An industrial trial study was carried out at Uddeholm Tooling AB, Sweden, to investigate the mechanisms of the formation of inclusions, especially macro inclusions during ingot casting. Strong evidence of reoxidation was observed. Two types of inclusions generated during casting were detected in the ingot. Inclusions of Type C1 originated from mould powder with reoxidation product Al2O3 as a part of it. Inclusions of this type were usually small. The number of Type C1 inclusions increased from the centre of the ingot toward the side wall of the mould. Type C2 inclusions were macro size. They could be the results of reoxidation and erosion of runner.
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4159.
  •  
4160.
  • Rahaman, Moshiour, et al. (författare)
  • Augmented-space cluster coherent potential approximation for binary random and short-range ordered alloys
  • 2009
  • Ingår i: Physical Review B. Condensed Matter and Materials Physics. - 1098-0121 .- 1550-235X. ; 79:5, s. 054201-
  • Tidskriftsartikel (refereegranskat)abstract
    • We use the earlier ideas of Razee and Prasad [Phys. Rev. B 45, 3265 (1992); Phys. Rev. B 48, 1349 (1993)], Datta [Phys. Rev. B 48, 8567 (1993)], and Mookerjee and Prasad [Phys. Rev. B 48, 17724 (1993)] to propose and implement a cluster generalization of the coherent potential approximation within a tight-binding linear muffin-tin orbital minimal basis set for binary alloys which are either random or have short-range order. In particular, we shall apply the technique to the CuZn alloys and compare it with other approaches.
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