A single-phase aluminium alloy (Al–0.1%Mg) and alloys containing large (⩾1 μm) second-phase particles (AA1200 and AA8006), which were deformed by cold rolling have been found to undergo either ...discontinuous or continuous recrystallization on subsequent annealing. It is found that continuous recrystallization occurs in samples in which a critical fraction of high angle boundaries are formed on deformation, and this is shown to be in agreement with a theory of microstructural stability. Continuous recrystallization is found to be promoted by a small initial grain size, large second-phase particles, and large strains. The mechanism of continuous recrystallization is thought to involve the collapse and subsequent coarsening of the lamellar grain structures produced on rolling to large strains.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UL, UM, UPCLJ, UPUK
The microstructures developed during deformation to large rolling strains in single and two-phase aluminium alloys with a wide range of grain sizes has been investigated, and the major parameters of ...the microstructure determined by high resolution electron backscatter diffraction (EBSD). It is found that the behaviour of initially fine-grained (<5 μm) alloys is significantly different from that of the large-grained (>50 μm) alloys. In the finer-grained alloys no significant grain fragmentation occurs, and at larger strains, when the spacing of high angle boundaries approaches the crystallite size, a considerable amount of the high angle boundary is removed by a process of dynamic recovery.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UL, UM, UPCLJ, UPUK
A sample of AISI type 316 stainless steel from a power station steam header, showing reheat cracking, was removed from service and has been examined by a combination of microscale X-ray computed ...tomography (CT), nanoscale serial section focused ion beam-scanning electron microscopy (FIB-SEM), energy dispersive X-ray (EDX) spectrum imaging and transmission electron microscopy (TEM). Multiscale three-dimensional analysis using correlative tomography allowed key regions to be found and analysed with high resolution techniques. The grain boundary analysed was decorated with micrometre sized, facetted cavities, M
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carbides, ferrite and G phase but no σ phase. Smaller intragranular M
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particles were also observed, close to the grain boundaries. This intimate coexistence suggests that the secondary phases will control the nucleation and growth of the cavities. Current models of cavitation, based on isolated idealised grain boundary cavities, are oversimplified.
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DOBA, IZUM, KILJ, NUK, PILJ, PNG, SAZU, UILJ, UKNU, UL, UM, UPUK
A study of creep cavities near reheat cracking in AISI Type 316H austenitic stainless steel headers, removed from prolonged high temperature operation in nuclear power plants, is reported. It is ...shown how application of scanning electron microscopy (SEM), cryogenic fractography and small angle neutron scattering (SANS) can be applied, in a complementary way, to observe and quantify creep cavitation. Creep cavities in the vicinity of the crack are found to be mainly surrounding inter-granular carbides. Trends in the size and area fraction of creep cavities relative to the crack path are quantified using optimised metallography. The SANS technique is found to be a very suitable method of quantifying creep cavitation within the size range up to 600 nm averaged over a larger gauge volume. It is shown that the cavity size distribution peaks in the region 100-300 nm, and this correlates closely with the quantitative SEM observations.
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DOBA, IZUM, KILJ, NUK, PILJ, PNG, SAZU, UILJ, UKNU, UL, UM, UPUK
In the present paper, the use of small angle neutron scattering to study creep cavitation around reheat cracking in two 316H austenitic stainless steel header components is reported. The components ...had been removed after long time high temperature operation in nuclear power plants. Cavities up to 350 nm in size are quantified, and their distribution relative to the crack, near the crack origin and away from the crack tip along the crack direction, is measured. Cavitation increases significantly on approaching the crack near the crack mouth. Cavitation is less prominent near the crack tip with minimal variation away from the crack tip. More extensive cavitation near the crack is found in the component with the longer reheat crack.
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DOBA, IZUM, KILJ, NUK, PILJ, PNG, SAZU, UILJ, UKNU, UL, UM, UPUK
Summary
The use of high‐resolution electron backscatter diffraction in the scanning electron microscope to quantify the volume fraction of recrystallization and the recrystallization kinetics is ...discussed. Monitoring the changes of high‐angle grain boundary (HAGB) content during annealing is shown to be a reliable method of determining the volume fraction of recrystallization during discontinuous recrystallization, where a large increase in the percentage of high‐angle boundaries occurs during annealing. The results are shown to be consistent with the standard methods of studying recrystallization, such as quantitative metallography and hardness testing. Application of the method to a highly deformed material has shown that it can be used to identify the transition from discontinuous to continuous recrystallization during which there is no significant change in the percentage of HAGB during annealing.
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BFBNIB, DOBA, FZAB, GIS, IJS, IZUM, KILJ, NLZOH, NUK, OILJ, PILJ, PNG, SAZU, SBCE, SBMB, SIK, UILJ, UKNU, UL, UM, UPUK
The presence of ductal disruption in pancreatic trauma is a major indicator of severity leading to higher morbidities and prolonged hospital stay. However, the adoption of early interventional ...approach in selected cases of documented grade III pancreatic trauma could result in shorter hospitalization and early recovery. We are describing our approach of early presentation-tailored interventions in managing two consecutive children diagnosed with grade III pancreatic injuries, which constitute the two main ends of the presentations' spectrum. For the early presenter a spleen preserving distal pancreatectomy was performed, while for the late presenter with large symptomatic pseudocyst endoscopic drainage was attempted. Both early and late presenting children had quick and uneventful recoveries leading to 5 and 6 days of hospitalization, respectively. Both cases continued to be asymptomatic at 4 and 12 months post procedure. In the pseudocyst case, the gastro-cystostomy stents were removed after 10 weeks, and 2.5 months later a completely healed pancreas was demonstrated by magnetic resonance cholangio-pancreatography. Unlike other abdominal solid organ injuries in children, adopting early presentation-tailored intervention can be associated with quicker recovery and short hospitalization for grade III pancreatic injuries. While the series is still small, achieving such remarkable outcomes in two consecutive cases is possible and could set a new trend in managing these injuries in children.
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IZUM, KILJ, NUK, PILJ, PNG, SAZU, UL, UM, UPUK
Small Angle Neutron Scattering (SANS) and Scanning Electron Microscopy (SEM) have been used to determine the degree of cavitation damage, of length scale 5-300 nm, associated with a creep crack grown ...in a compact tension specimen cut from a Type 316H stainless steel weldment. The specimen was supplied by EDF Energy as part of an extensive study of creep crack growth in the heat affected zone of reactor components. The creep crack propagates along a line 1.5 mm away from, and parallel to, the weld fusion line boundary before deviating away into parent material. The SANS results show a systematic increase in fractional size distribution of cavities approaching the crack, along lines normal to the crack line, and along lines parallel to the crack line approaching the crack mouth. Both SANS and quantitative metallography measurements using SEM indicate two populations of cavities: smaller cavities of less than 100 nm size having a mean diameter of about 60 nm, and a population of larger cavities of 100-300 nm size with a mean diameter of about 200 nm.
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GEOZS, IJS, IMTLJ, KILJ, KISLJ, NLZOH, NUK, OILJ, PNG, SAZU, SBCE, SBJE, UILJ, UL, UM, UPCLJ, UPUK, ZAGLJ, ZRSKP
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