178 research outputs found
Performance of the Yb/<i>n< Tunneling Barriers
No full textQasrawi, Atef Fayez/0000-0001-8193-6975In this article, the design and performance of the CdSe which are deposited onto thin films of Yb metal is reported and discussed. The thin films of CdSe which are deposited by the physical vapor deposition technique are observed to exhibit slightly deformed hexagonal polycrystalline nature with excess amount of Cd as confirmed by the X-ray, energy dispersive X-ray spectroscopy and scanning electron microscopy techniques. The n-type CdSe is also found to form a Schottky barrier of tunneling type when sandwiched between Yb and carbon. The quantum mechanical tunneling mechanism in this device which was tested and modeled in the frequency domain of 10-150 MHz is found to exhibit average intersite separations of similar to 5 nm. The tunneling device exhibited a widening in the depletion region associated with significantly large capacitance tunability in the studied frequency domain. On the other hand, as an optoelectronic device, the Yb/n-CdSe/C Schottky diode exhibited a responsivity of similar to 0.10 NW, photosensitivity of 6.5 x 10(4) and external quantum efficiency of 54% when biased with 1.0 V and exposed to laser light of wavelength of 406 nm.Arab American University, Jenin, Palestine; DSRThis project was funded by the Deanship of Scientific Research at Arab American University, Jenin, Palestine. The author, therefore, acknowledge with thanks the DSR for technical and financial support
Effect of microstructure on mechanical properties of a novel high-Mn TWIP stainless steel bearing vanadium
No full textDeformation and Damage Mechanisms in Ultrafine-Grained Austenitic Stainless Steel During Cyclic Straining
No full textManufacturing, mechanical properties and corrosion behaviour of high-Mn TWIP steels
No full textAbstractAustenitic high-Mn (15–30 wt.%) based twinning-induced plasticity (TWIP) steels provide great potential in applications for structural components in the automotive industry, owing to their excellent tensile strength-ductility property combination. In certain cases, these steels might also substitute austenitic Cr-Ni stainless steels. The aim of this present work is to investigate the high-temperature flow resistance, recrystallisation and the evolution of microstructure of high-Mn steels by compression testing on a Gleeble simulator. The influence of Al alloying (0–8 wt.%) in the hot rolling temperature range (800°C–1100°C) is studied in particular, but also some observations are made regarding the influence of Cr alloying. Microstructures are examined in optical and electron microscopes. The results are compared with corresponding properties of carbon and austenitic stainless steels. In addition, the mechanical properties are studied briefly, using tension tests over the temperature range from -80°C to 200°C. Finally, a preliminary study is conducted on the corrosion behaviour of TWIP steels in two media, using the potentiodynamic polarization technique.The results show that the flow stress level of high-Mn TWIP steels is considerably higher than that of low-carbon steels and depends on the Al concentration up to 6 wt.%, while the structure is fully austenitic at hot rolling temperatures. At higher Al contents, the flow stress level is reduced, due to the presence of ferrite. The static recrystallisation kinetics is slower compared to that of carbon steels, but it is faster than is typical of Nb-microalloyed or austenitic stainless steels. The high Mn content is one reason for high flow stress as well as for slow softening. Al plays a minor role only; but in the case of austenitic-ferritic structure, the softening of the ferrite phase occurs very rapidly, contributing to overall faster softening. The high Mn content also retards considerably the onset of dynamic recrystallisation, but the influence of Al is minor. Similarly, the contribution of Cr to the hot deformation resistance and static and dynamic recrystallisation, is insignificant. The grain size effectively becomes refined by the dynamic and static recrystallisation processes.The tensile testing of TWIP steels revealed that the Al alloying and temperature have drastic effects on the yield strength, tensile strength and elongation. The higher Al raises the yield strength because of the solid solution strengthening. However, Al tends to increase the stacking fault energy that affects strongly the deformation mechanism. In small concentrations, Al suppresses martensite formation and enhances deformation twinning, leading to high tensile strength and good ductility. However, with an increasing temperature, SFE increases, and consequently, the density of deformation twins decreases and mechanical properties are impaired.Corrosion testing indicated that Al alloying improves the corrosion resistance of high-Mn TWIP steels. The addition of Cr is a further benefit for the passivation of these steels. The passive film that formed on 8wt.% Al-6wt.%Cr steel was found to be even more stable than that on Type 304 steel in 5–50% HNO3 solutions. A prolonged pre-treatment of the steel in the anodic passive regime created a thick, protective and stable passive film that enhanced the corrosion resistance also in 3.5% NaCl solution.Academic dissertation to be presented, with the assent of the Faculty of Technology of the University of Oulu, for public defence in Auditorium TA105, Linnanmaa, on October 19th, 2007, at 12 noonAbstract
Austenitic high-Mn (15–30 wt.%) based twinning-induced plasticity (TWIP) steels provide great potential in applications for structural components in the automotive industry, owing to their excellent tensile strength-ductility property combination. In certain cases, these steels might also substitute austenitic Cr-Ni stainless steels. The aim of this present work is to investigate the high-temperature flow resistance, recrystallisation and the evolution of microstructure of high-Mn steels by compression testing on a Gleeble simulator. The influence of Al alloying (0–8 wt.%) in the hot rolling temperature range (800°C–1100°C) is studied in particular, but also some observations are made regarding the influence of Cr alloying. Microstructures are examined in optical and electron microscopes. The results are compared with corresponding properties of carbon and austenitic stainless steels. In addition, the mechanical properties are studied briefly, using tension tests over the temperature range from -80°C to 200°C. Finally, a preliminary study is conducted on the corrosion behaviour of TWIP steels in two media, using the potentiodynamic polarization technique.
The results show that the flow stress level of high-Mn TWIP steels is considerably higher than that of low-carbon steels and depends on the Al concentration up to 6 wt.%, while the structure is fully austenitic at hot rolling temperatures. At higher Al contents, the flow stress level is reduced, due to the presence of ferrite. The static recrystallisation kinetics is slower compared to that of carbon steels, but it is faster than is typical of Nb-microalloyed or austenitic stainless steels. The high Mn content is one reason for high flow stress as well as for slow softening. Al plays a minor role only; but in the case of austenitic-ferritic structure, the softening of the ferrite phase occurs very rapidly, contributing to overall faster softening. The high Mn content also retards considerably the onset of dynamic recrystallisation, but the influence of Al is minor. Similarly, the contribution of Cr to the hot deformation resistance and static and dynamic recrystallisation, is insignificant. The grain size effectively becomes refined by the dynamic and static recrystallisation processes.
The tensile testing of TWIP steels revealed that the Al alloying and temperature have drastic effects on the yield strength, tensile strength and elongation. The higher Al raises the yield strength because of the solid solution strengthening. However, Al tends to increase the stacking fault energy that affects strongly the deformation mechanism. In small concentrations, Al suppresses martensite formation and enhances deformation twinning, leading to high tensile strength and good ductility. However, with an increasing temperature, SFE increases, and consequently, the density of deformation twins decreases and mechanical properties are impaired.
Corrosion testing indicated that Al alloying improves the corrosion resistance of high-Mn TWIP steels. The addition of Cr is a further benefit for the passivation of these steels. The passive film that formed on 8wt.% Al-6wt.%Cr steel was found to be even more stable than that on Type 304 steel in 5–50% HNO3 solutions. A prolonged pre-treatment of the steel in the anodic passive regime created a thick, protective and stable passive film that enhanced the corrosion resistance also in 3.5% NaCl solution
Manufacturing, mechanical properties and corrosion behaviour of high-Mn TWIP steels
No full textAbstract
Austenitic high-Mn (15–30 wt.%) based twinning-induced plasticity (TWIP) steels provide great potential in applications for structural components in the automotive industry, owing to their excellent tensile strength-ductility property combination. In certain cases, these steels might also substitute austenitic Cr-Ni stainless steels. The aim of this present work is to investigate the high-temperature flow resistance, recrystallisation and the evolution of microstructure of high-Mn steels by compression testing on a Gleeble simulator. The influence of Al alloying (0–8 wt.%) in the hot rolling temperature range (800°C–1100°C) is studied in particular, but also some observations are made regarding the influence of Cr alloying. Microstructures are examined in optical and electron microscopes. The results are compared with corresponding properties of carbon and austenitic stainless steels. In addition, the mechanical properties are studied briefly, using tension tests over the temperature range from -80°C to 200°C. Finally, a preliminary study is conducted on the corrosion behaviour of TWIP steels in two media, using the potentiodynamic polarization technique.
The results show that the flow stress level of high-Mn TWIP steels is considerably higher than that of low-carbon steels and depends on the Al concentration up to 6 wt.%, while the structure is fully austenitic at hot rolling temperatures. At higher Al contents, the flow stress level is reduced, due to the presence of ferrite. The static recrystallisation kinetics is slower compared to that of carbon steels, but it is faster than is typical of Nb-microalloyed or austenitic stainless steels. The high Mn content is one reason for high flow stress as well as for slow softening. Al plays a minor role only; but in the case of austenitic-ferritic structure, the softening of the ferrite phase occurs very rapidly, contributing to overall faster softening. The high Mn content also retards considerably the onset of dynamic recrystallisation, but the influence of Al is minor. Similarly, the contribution of Cr to the hot deformation resistance and static and dynamic recrystallisation, is insignificant. The grain size effectively becomes refined by the dynamic and static recrystallisation processes.
The tensile testing of TWIP steels revealed that the Al alloying and temperature have drastic effects on the yield strength, tensile strength and elongation. The higher Al raises the yield strength because of the solid solution strengthening. However, Al tends to increase the stacking fault energy that affects strongly the deformation mechanism. In small concentrations, Al suppresses martensite formation and enhances deformation twinning, leading to high tensile strength and good ductility. However, with an increasing temperature, SFE increases, and consequently, the density of deformation twins decreases and mechanical properties are impaired.
Corrosion testing indicated that Al alloying improves the corrosion resistance of high-Mn TWIP steels. The addition of Cr is a further benefit for the passivation of these steels. The passive film that formed on 8wt.% Al-6wt.%Cr steel was found to be even more stable than that on Type 304 steel in 5–50% HNO3 solutions. A prolonged pre-treatment of the steel in the anodic passive regime created a thick, protective and stable passive film that enhanced the corrosion resistance also in 3.5% NaCl solution
Effect of electroslag refining on cleanness, microstructure and mechanical properties of a newly developed crnimowmnv ultrahigh-strength steel
No full textThe cleanness, microstructure and mechanical properties of a newly developed CrNiMoWMnV ultrahigh-strength steel with and without electroslag refining (ESR) with 70% CaF2, 15% Al2 O3 and 15% CaO have been studied. This steel was designed and melted in an air induction furnace followed by refining using ESR. Cast ingots with and without ESR were forged at temperatures in the range 1100-950oC. Laser scanning confocal microscopy, field emission scanning electron microscopy electron back scattering diffraction, electron probe microanalysis and X-ray diffraction have been used to investigate the microstructure and non-metallic inclusions (NMIs) of forged ingots produced with and without ESR. Hardness, tensile and Charpy-V impact tests were performed. ESR reduced the total impurity level i.e. O%+ N%+ S% by 26 % and the area fractions and numbers of NMIs by 17% and 7% respectively. The NMIs are classified into four major classes: oxides, sulphides, nitrides and complex multiphase inclusions. The microstructure of the forged and air-cooled bars consisted of martensite with a small fraction of distributed retained austenite, a very small fraction of bainite and finely distributed precipitates. The reduction of impurity levels combined with the microstructural changes brought about by the changes in the chemical composition meant that ESR resulted in a significant improvement in some mechanical properties and a marginal improvement in others.</p
Promotion of thermomechanical processing of 2-GPa low-alloyed ultrahigh-strength steel and physically based modelling of the deformation behaviour
No full textAbstractA low-alloyed ultrahigh-strength steel comprising CrNiMoWMnV was designed based on thermodynamic calculations and by controlling the microalloying elements to promote various strengthening mechanisms upon processing. The hot deformation behaviour and mechanism were correlated with the processing parameters, that is, strain rate and temperature. The fine features of the deformed microstructures were analysed using electron backscatter diffraction (EBSD) and MATLAB software, combined with the MTEX texture and crystallographic analysis toolbox. The flow stress behaviour at high temperatures was modelled using the dislocation density-based Bergström’s model, which could be applied up to the peak strain. However, the diffusional transformation (i.e. recrystallisation)-based Kolmogorov–Johnson–Mehl–Avrami model has been applied to fit the flow stress over a wide deformation strain. The effective grain size (EGS) of martensite and prior austenite grain size (PAGS) were correlated with the deformation temperature and strain rate. Because the PAGS was significantly refined from 16 μm in the initial microstructure to 6 μm after processing at 850 °C/0.01 s-1, the corresponding martensite EGSs were 1.38 and 1.01 μm, respectively. Therefore, these fine-controlled characteristics of the processed microstructures at high temperatures help to enhance the mechanical properties, such as the strength and toughness, of the designed ultrahigh-strength steel.Abstract
A low-alloyed ultrahigh-strength steel comprising CrNiMoWMnV was designed based on thermodynamic calculations and by controlling the microalloying elements to promote various strengthening mechanisms upon processing. The hot deformation behaviour and mechanism were correlated with the processing parameters, that is, strain rate and temperature. The fine features of the deformed microstructures were analysed using electron backscatter diffraction (EBSD) and MATLAB software, combined with the MTEX texture and crystallographic analysis toolbox. The flow stress behaviour at high temperatures was modelled using the dislocation density-based Bergström’s model, which could be applied up to the peak strain. However, the diffusional transformation (i.e. recrystallisation)-based Kolmogorov–Johnson–Mehl–Avrami model has been applied to fit the flow stress over a wide deformation strain. The effective grain size (EGS) of martensite and prior austenite grain size (PAGS) were correlated with the deformation temperature and strain rate. Because the PAGS was significantly refined from 16 μm in the initial microstructure to 6 μm after processing at 850 °C/0.01 s-1, the corresponding martensite EGSs were 1.38 and 1.01 μm, respectively. Therefore, these fine-controlled characteristics of the processed microstructures at high temperatures help to enhance the mechanical properties, such as the strength and toughness, of the designed ultrahigh-strength steel
Atlas for water consumption (ETc) and amount of irrigation water used (IR) for Egyptian crops over three decades (1985-2015): Part 1: North Nile Delta Region
No full textThe agricultural land in Egypt is nearly irrigated of about 98% due to the very dry conditions i.e. no rain fed agriculture from economic point of view is implemented. Capita share per annum from water is less than the poverty edge of 1000 m3 and it is continuously decreasing till the water scarcity level of less than 500 m3 in the few coming decades. In addition, population growth, climate change and development projects all this will increase the pressure on already limited water resources. So, the water conservation procedures and rationalization of use has become imperative at all levels.
Ministry of agriculture and land reclamation in Egypt always seek to maximize the exploitation of natural resources. So it has set up a new strategy "sustainable agricultural development strategy 2030 ."
The current study aims to estimate reference evapotranspiration and water consumption for crops grown in Nile Delta region through the last three decades (1985-2015). In addition, estimation of water needs at the farm level and Aswan High Dam
Enhancement and underlying fatigue mechanisms of laser powder bed fusion additive-manufactured 316L stainless steel
No full textAbstractIn this study, the enhancement of additively manufactured (AM) 316L, by annealing, to the fully reversed tension-compression fatigue performance, in terms of fatigue life and fatigue damage, were investigated under two conditions: as-built (AB) and heat-treated (HT) at 900 °C. The underlying fatigue mechanisms were comprehensively characterised through intensive microstructural observations of cyclic-strained microstructures and fracture surfaces using laser confocal scanning microscopy (LCSM) and secondary electron imaging using scanning electron microscopy (SEM). The experimental results showed that the fatigue resistance of HT 316L was significantly enhanced by 100% as the fatigue limit was increased from 75 to 150 MPa for AB and HT 316L, respectively. The fatigue cracking mechanism in AB 316L is mainly related to two imperfections of the AM-induced microstructural components: residual stresses, which cause highly localised deformation, and dendritic cellular structures, which possess a weak link in their grain boundaries against crack propagation. Upon heat treatment at 900 °C, the residual stresses and dendritic structure were effectively reduced. Consequently, the fatigue life of AM 316L was significantly enhanced by promoting the formation of high-angle boundaries. More precisely, the cyclic deformation processes in fatigued HT 316L involve persistent slip bands and strain hardening. Abstract
In this study, the enhancement of additively manufactured (AM) 316L, by annealing, to the fully reversed tension-compression fatigue performance, in terms of fatigue life and fatigue damage, were investigated under two conditions: as-built (AB) and heat-treated (HT) at 900 °C. The underlying fatigue mechanisms were comprehensively characterised through intensive microstructural observations of cyclic-strained microstructures and fracture surfaces using laser confocal scanning microscopy (LCSM) and secondary electron imaging using scanning electron microscopy (SEM). The experimental results showed that the fatigue resistance of HT 316L was significantly enhanced by 100% as the fatigue limit was increased from 75 to 150 MPa for AB and HT 316L, respectively. The fatigue cracking mechanism in AB 316L is mainly related to two imperfections of the AM-induced microstructural components: residual stresses, which cause highly localised deformation, and dendritic cellular structures, which possess a weak link in their grain boundaries against crack propagation. Upon heat treatment at 900 °C, the residual stresses and dendritic structure were effectively reduced. Consequently, the fatigue life of AM 316L was significantly enhanced by promoting the formation of high-angle boundaries. More precisely, the cyclic deformation processes in fatigued HT 316L involve persistent slip bands and strain hardening
- …
