The Experts below are selected from a list of 17154 Experts worldwide ranked by ideXlab platform
Jean Marc Olive - One of the best experts on this subject based on the ideXlab platform.
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effects of microstructure and local mechanical fields on intergranular stress corrosion cracking of a friction stir welded aluminum copper lithium 2050 nugget
2014Co-Authors: Matthieu Dhondt, Isabelle Aubert, Nicolas Saintier, Jean Marc OliveAbstract:Abstract The effects of the microstructure and mechanical fields on intergranular stress corrosion cracking (IGSCC) of the nugget zone of heat treated welds obtained by friction stir welding in the AA2050 aluminum alloy have been investigated at different scales. At low strain rate, in 1.0 NaCl aqueous solution, IGSCC develops in the microstructure, whereas only pitting corrosion is observed without any mechanical stress. Based on surface observations, EBSD analysis and X-ray tomography, the key role of sub-millimetric textured bands (induced by the welding process) on the IGSCC is demonstrated. Analyses at a more local scale show the grain Boundary (low Angle Boundary, special coincident site lattice Boundary or High Angle Boundary) do not have a significant effect on crack initiation. Crystal plasticity finite element calculations show that the threshold normal stress at grain boundaries for IGSCC development is about 80% of the macroscopic stress. It is also Highlighted by crystal plasticity calculations that there is a drastic effect of the local stress field on the shape of cracks. Finally, it is shown that plasticity induced residual stresses are sufficient for the formation of IGSCC.
Chris P Heason - One of the best experts on this subject based on the ideXlab platform.
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grain structure formation during friction stir welding observed by the stop action technique
2005Co-Authors: P B Prangnell, Chris P HeasonAbstract:Abstract Experiments have been carried out to ‘freeze’ the friction stir welding process by stopping the tool and immediately quenching the work piece in an Al-2195 plate welded under typical conditions. Sectioning through the ‘frozen’ weld keyhole with the tool in place has allowed the microstructure development, leading to the formation of the ultrafine grained nugget material, to be directly observed as fresh material encounters the deformation field surrounding the rotating pin. The grain refinement process is shown to be driven by grain subdivision at the colder periphery of the tools deformation zone, and the geometric effects of strain, which together reduce the overall High Angle Boundary spacing with increasing deformation. However, it also involves thermally activated High Angle grain Boundary migration, which increases as the temperature rises towards the tool. The Higher temperature latter stages of the refinement process are closely reminiscent of geometric dynamic recrystallisation seen in High strain hot torsion experiments. The nugget grain structure has also been found to become more equiaxed and coarsens slightly, due to static annealing in the thermal wake of the tool.
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grain structure formation during friction stir welding observed by the stop action technique
2005Co-Authors: P B Prangnell, Chris P HeasonAbstract:Abstract Experiments have been carried out to ‘freeze’ the friction stir welding process by stopping the tool and immediately quenching the work piece in an Al-2195 plate welded under typical conditions. Sectioning through the ‘frozen’ weld keyhole with the tool in place has allowed the microstructure development, leading to the formation of the ultrafine grained nugget material, to be directly observed as fresh material encounters the deformation field surrounding the rotating pin. The grain refinement process is shown to be driven by grain subdivision at the colder periphery of the tools deformation zone, and the geometric effects of strain, which together reduce the overall High Angle Boundary spacing with increasing deformation. However, it also involves thermally activated High Angle grain Boundary migration, which increases as the temperature rises towards the tool. The Higher temperature latter stages of the refinement process are closely reminiscent of geometric dynamic recrystallisation seen in High strain hot torsion experiments. The nugget grain structure has also been found to become more equiaxed and coarsens slightly, due to static annealing in the thermal wake of the tool.
P B Prangnell - One of the best experts on this subject based on the ideXlab platform.
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loss of High Angle Boundary area during annealing a cryo spd processed al alloy with a nano scale lamellar grain structure
2012Co-Authors: Yan Huang, G H Zahid, P B PrangnellAbstract:The grain structure and texture evolution during annealing an Al-0.13%Mg submicron grained alloy, deformed by plane strain compression (PSC) at cryogenic temperatures, has been investigated. On annealing the grain structure coarsened and transformed from lamellar to equiaxed. But, remarkably, the fraction of low Angle boundaries (LABs) increased, from less than ~ 25% to ~50% above 300 °C, leading to instability and discontinuous coarsening at Higher temperatures. The surprisingly large increase in LAB fraction on annealing is shown to be related to orientation impingement originating from the strong texture present after PSC in liquid nitrogen.
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grain structure formation during friction stir welding observed by the stop action technique
2005Co-Authors: P B Prangnell, Chris P HeasonAbstract:Abstract Experiments have been carried out to ‘freeze’ the friction stir welding process by stopping the tool and immediately quenching the work piece in an Al-2195 plate welded under typical conditions. Sectioning through the ‘frozen’ weld keyhole with the tool in place has allowed the microstructure development, leading to the formation of the ultrafine grained nugget material, to be directly observed as fresh material encounters the deformation field surrounding the rotating pin. The grain refinement process is shown to be driven by grain subdivision at the colder periphery of the tools deformation zone, and the geometric effects of strain, which together reduce the overall High Angle Boundary spacing with increasing deformation. However, it also involves thermally activated High Angle grain Boundary migration, which increases as the temperature rises towards the tool. The Higher temperature latter stages of the refinement process are closely reminiscent of geometric dynamic recrystallisation seen in High strain hot torsion experiments. The nugget grain structure has also been found to become more equiaxed and coarsens slightly, due to static annealing in the thermal wake of the tool.
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grain structure formation during friction stir welding observed by the stop action technique
2005Co-Authors: P B Prangnell, Chris P HeasonAbstract:Abstract Experiments have been carried out to ‘freeze’ the friction stir welding process by stopping the tool and immediately quenching the work piece in an Al-2195 plate welded under typical conditions. Sectioning through the ‘frozen’ weld keyhole with the tool in place has allowed the microstructure development, leading to the formation of the ultrafine grained nugget material, to be directly observed as fresh material encounters the deformation field surrounding the rotating pin. The grain refinement process is shown to be driven by grain subdivision at the colder periphery of the tools deformation zone, and the geometric effects of strain, which together reduce the overall High Angle Boundary spacing with increasing deformation. However, it also involves thermally activated High Angle grain Boundary migration, which increases as the temperature rises towards the tool. The Higher temperature latter stages of the refinement process are closely reminiscent of geometric dynamic recrystallisation seen in High strain hot torsion experiments. The nugget grain structure has also been found to become more equiaxed and coarsens slightly, due to static annealing in the thermal wake of the tool.
Matthieu Dhondt - One of the best experts on this subject based on the ideXlab platform.
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effects of microstructure and local mechanical fields on intergranular stress corrosion cracking of a friction stir welded aluminum copper lithium 2050 nugget
2014Co-Authors: Matthieu Dhondt, Isabelle Aubert, Nicolas Saintier, Jean Marc OliveAbstract:Abstract The effects of the microstructure and mechanical fields on intergranular stress corrosion cracking (IGSCC) of the nugget zone of heat treated welds obtained by friction stir welding in the AA2050 aluminum alloy have been investigated at different scales. At low strain rate, in 1.0 NaCl aqueous solution, IGSCC develops in the microstructure, whereas only pitting corrosion is observed without any mechanical stress. Based on surface observations, EBSD analysis and X-ray tomography, the key role of sub-millimetric textured bands (induced by the welding process) on the IGSCC is demonstrated. Analyses at a more local scale show the grain Boundary (low Angle Boundary, special coincident site lattice Boundary or High Angle Boundary) do not have a significant effect on crack initiation. Crystal plasticity finite element calculations show that the threshold normal stress at grain boundaries for IGSCC development is about 80% of the macroscopic stress. It is also Highlighted by crystal plasticity calculations that there is a drastic effect of the local stress field on the shape of cracks. Finally, it is shown that plasticity induced residual stresses are sufficient for the formation of IGSCC.
Chengjia Shang - One of the best experts on this subject based on the ideXlab platform.
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carbon microalloying effect of base material on variant selection in coarse grained heat affected zone of x80 pipeline steel
2019Co-Authors: Xuemin Wang, X P, Z Q Wang, S V Subramanian, Chengjia Shang, X C LiAbstract:Abstract The carbon is one of the basic alloying solutes in steels. In the present study, the newly carbon microalloyed X80 steel was designed for the next generation of pipeline and the carbon microalloying effect of base material on the crystallographic structure of coarse grained heat affected zone (CGHAZ) of X80 girth welded joints was systematically investigated using electron back-scattering diffraction (EBSD), considering the fact that crystallography is the most intrinsic aspect in evaluating the microstructure. The results indicated a remarkable variation in the density of High Angle grain boundaries and their dispersion by increasing the carbon content of 0.03wt%. It was attributed to the differential shearing mechanism, which was primarily sheared by variant pairing of V1/V2 at 0.06 wt% carbon, whereas at lower 0.03wt% carbon, V1/V4 pairing mechanism dominated the transformation. The preferential variant pairing transformation mechanism at differential carbon content therefore generated dissimilarly selected variants. Thus, as the carbon content increased, the variant selection effect upon phase transformation was attenuated by generating more variants from different Bain groups. The variant pair V1/V2 belonging to different Bain groups neighboring in CGHAZ of High carbon steel increased the density of High Angle Boundary (Σ3 Boundary). Moreover, the variation in CTOD (crack-tip opening displacement) property of HAZ suggested that it should be primarily correlated to the block size (or density of block boundaries) of CGHAZ.
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ebsd characterization of secondary microcracks in the heat affected zone of a x100 pipeline steel weld joint
2015Co-Authors: S V Subramanian, Chengjia ShangAbstract:In order to get better understanding of the mechanism of cleavage fracture in the heat affected zone (HAZ) of X100 pipeline steel, secondary microcracks underneath the brittle fracture surface of a Charpy impacted sample with the notch located in the HAZ were characterized using electron backscattered diffraction. Since the coarse grained (CG) HAZ and intercritically reheated coarse grained (ICCG) HAZ are well accepted as the weakest region in the HAZ, the cleavage secondary microcracks in these two regions were observed respectively. Initiation and propagation of cleavage microcracks were discussed. The results show that the fracture behavior is obviously influenced by local microstructure. There are more secondary microcracks in the ICCGHAZ than in the CGHAZ which shows different probability for microcrack nucleation. Fracture mechanism changes from nucleation control in the CGHAZ to propagation control in the ICCGHAZ. The main reason for the increased possibility of secondary microcracks formation and the change in fracture mechanism is due to the formation of coarse necklacing martensite–austenite constituent in the ICCGHAZ. The results also show that High Angle Boundary, with the misorientation larger than $$45^{\,\circ }$$ , is effective in deflecting or arresting brittle cracks, while low Angle Boundary ( $$15^{\,\circ }{-}45^{\,\circ }$$ ) seems not. Most preferred crack planes are {100}, with decreasing probability of {110}, {112}, {123}.
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investigation on the microstructure and toughness of coarse grained heat affected zone in x 100 multi phase pipeline steel with High nb content
2012Co-Authors: Chengjia Shang, Nie Wenjin, Sundaresa SubramanianAbstract:Abstract Effect of increasing heat input on microstructure evolution and impact toughness of coarse grained heat affected zone (CGHAZ) in High Nb X-100 multi-phase pipeline steel was investigated by means of Gleeble simulator, optical microscope (OM), scanning electron microscope (SEM) and electron backscattering diffraction (EBSD). Charpy impact test confirmed the optimum toughness of CGHAZ was achieved at heat input of 20 kJ/cm, equivalent to the excellent toughness of the base plate. Observations performed by OM, SEM and EBSD show that the microstructure of CGHAZ varies dramatically with heat input without a noticeable changing in prior austenite grain size, and the optimum toughness achieved at the heat input of 20 kJ/cm is related to the cumulative contribution of its well-refined martensite/austenite (M/A) constituent and the Highest density of High Angle boundaries. Analysis on crystallography shows that High Angle boundaries are mainly the boundaries between the products from different Bain groups produced from the fcc to bcc coherent transformation within prior austenite grain, and the density of High Angle Boundary is controlled by the configuration of Bain groups within the crystallographic packet in each austenite grain. With the ideal configuration, the density of High Angle Boundary can be optimized to be beneficial to keep High toughness in CGHAZ, together with well-refined M/A constituent. This indicates that in addition to M/A refinement, the characteristic in crystallography of the crystallographic packet (the configuration of Bain groups within it) is related to the mechanical properties of CGHAZ and should be controlled to be optimum.