Constant Current Density Compression Behavior of 304 Stainless Steel and Ti-6Al-4V During Electrically-Assisted Forming

2011 ◽  
Author(s):  
Joshua J. Jones ◽  
Laine Mears
Keyword(s):  
Stainless Steel ◽  
Flow Stress ◽  
Current Density ◽  
Elevated Temperatures ◽  
Shape Change ◽  
Electrical Current ◽  
304 Stainless Steel ◽  
Constant Current ◽  
Constant Current Density ◽  
Electrically Assisted

A metal forming technique which has more recently come of interest as an alternative to processes that use elevated temperatures at some stage during manufacturing is Electrically-Assisted Forming (EAF). EAF is a processing technique which applies electrical current through the workpiece concurrently while the material is being formed. At present, this method has only been studied on an experimental level in laboratory settings, and the heuristic results show increased fracture strain, reduced flow stress, and reduced springback; the enhanced process capability is beyond the range that would be expected from pure resistive heating alone. Thus far, when applying the electrical current through the workpiece during deformation, the current magnitude flowing through the workpiece has remained constant. Hence, for a compression loading, the current flux or density decreases as a result of an increasing specimen area. This work examines the effect of a non-constant current density (NCCD) and a constant current density (CCD) on the deformation behavior of 304 Stainless Steel and Ti-6Al-4V during uniaxial compression testing. Additionally, the application of a CCD is used to modify existing empirically-based EAF flow stress models for these materials. From this testing, it is shown that a CCD during forming can significantly reduce the flow stress of the material as compared to the NCCD tests. The reductions in the flow stress were increased at higher strains by approximately 30% and 15% for the 304 Stainless Steel and Ti-6Al-4V, respectively. More importantly, these flow stress curves are better representative of how the material responds to an applied electrical current as the specimen shape change is removed from the results. Also, the NCCD tests were approximated using an existing empirically-based EAF flow stress model and the CCD tests concluded that a new flow stress predictor model be introduced.

Modeling of Size Effects on the Flow Stress of Type 304 Stainless Steel and Application in Coining Process

2007 ◽  
Author(s):  
Gap-Yong Kim ◽  
Muammer Koc ◽  
Jun Ni
Keyword(s):  
Grain Size ◽  
Stainless Steel ◽  
Flow Stress ◽  
Size Effect ◽  
Size Effects ◽  
Specimen Size ◽  
304 Stainless Steel ◽  
Length Scales ◽  
Type 304 ◽  
Type 304 Stainless Steel

Application of microforming in various research areas has received much attention due to the increased demand for miniature metallic parts that require mass production. For the accurate analysis and design of microforming process, proper modeling of material behavior at the micro/meso-scale is necessary by considering the size effects. Two size effects are known to exist in metallic materials. One is the “grain size” effect, and the other is the “feature/specimen size” effect. This study investigated the “feature/specimen size” effect and introduced a scaling model which combined both feature/specimen and grain size effects. Predicted size effects were compared with experiments obtained from previous research and showed a very good agreement. The model was also applied to forming of micro-features by coining. A flow stress model for Type 304 stainless steel taking into consideration the effect of the grain and feature size was developed and implemented into a finite element simulation tool for an accurate numerical analysis. The scaling model offered a simple way to model the size effect down to length scales of a couple of grains and extended the use of continuum plasticity theories to micro/meso-length scales.

Study on Special Morphology Hydroxyapatite Bioactive Coating by Electrochemical Deposition

2013 ◽  
Vol 537 ◽  
pp. 256-260
Author(s):  
Cai Ge Gu ◽  
Qian Gang Fu ◽  
He Jun Li ◽  
Jin Hua Lu ◽  
Lei Lei Zhang
Keyword(s):  
Electrochemical Deposition ◽  
Current Density ◽  
Electrolyte Concentration ◽  
Spherical Particles ◽  
Constant Current ◽  
Constant Current Density ◽  
Depth Direction ◽  
Special Morphology ◽  
Calcium Phosphate Coatings ◽  
Coating Weight

Bioactive calcium phosphate coatings were deposited on carbon/carbon（C/C） composites using electrochemical deposition technique. The effects of electrolyte concentration and constant current density on morphology, structure and composition of the coating were systematically investigated using scanning electron microscopy (SEM), X-ray diffraction (XRD) and Fourier transformed infrared (FTIR) spectroscopy. The results show that, the coating weight elevated gradually with the increase of electrolyte concentration, and the morphology of coatings changed from spherical particles to nanolamellar crystals with interlocking structure initially. Then the coating transformed into seaweed-like and nano/micro-sized crystals along the depth direction of the coating. The coatings showed seaweed-like morphology as the deposition current density was less than 20mA. With the less current density, the coating became more homogenous. However, the coating was fiakiness crysal, with needlike crystal stacked upside as the current density reached to 20mA/cm2. The coating weight was improved gradually when the current density increased from 2.5mA/cm2 to 10mA/cm2, then reduced with the increasing current density in the range of 10 to 20mA/cm2.

scholarly journals InAs/GaAs Quantum Dot Microlasers Formed on Silicon Using Monolithic and Hybrid Integration Methods

Materials ◽  
2020 ◽  
Vol 13 (10) ◽  
pp. 2315
Author(s):  
Alexey E. Zhukov ◽  
Natalia V. Kryzhanovskaya ◽  
Eduard I. Moiseev ◽  
Anna S. Dragunova ◽  
Mingchu Tang ◽  
...  
Keyword(s):  
Quantum Dot ◽  
Current Density ◽  
Elevated Temperatures ◽  
Continuous Wave ◽  
Electrical Contact ◽  
Threshold Current ◽  
Threshold Current Density ◽  
Constant Current ◽  
Surface Protection ◽  
Microdisk Lasers

An InAs/InGaAs quantum dot laser with a heterostructure epitaxially grown on a silicon substrate was used to fabricate injection microdisk lasers of different diameters (15–31 µm). A post-growth process includes photolithography and deep dry etching. No surface protection/passivation is applied. The microlasers are capable of operating heatsink-free in a continuous-wave regime at room and elevated temperatures. A record-low threshold current density of 0.36 kA/cm2 was achieved in 31 µm diameter microdisks operating uncooled. In microlasers with a diameter of 15 µm, the minimum threshold current density was found to be 0.68 kA/cm2. Thermal resistance of microdisk lasers monolithically grown on silicon agrees well with that of microdisks on GaAs substrates. The ageing test performed for microdisk lasers on silicon during 1000 h at a constant current revealed that the output power dropped by only ~9%. A preliminary estimate of the lifetime for quantum-dot (QD) microlasers on silicon (defined by a double drop of the power) is 83,000 h. Quantum dot microdisk lasers made of a heterostructure grown on GaAs were transferred onto a silicon wafer using indium bonding. Microlasers have a joint electrical contact over a residual n+ GaAs substrate, whereas their individual addressing is achieved by placing them down on a p-contact to separate contact pads. These microdisks hybridly integrated to silicon laser at room temperature in a continuous-wave mode. No effect of non-native substrate on device characteristics was found.

A Study on Warm Micro Backward Extrusion of SUS 304 Stainless Steel

2011 ◽  
Vol 486 ◽  
pp. 139-142
Author(s):  
Chao Cheng Chang ◽  
Dinh Hiep Nguyen ◽  
Hsin Sheng Hsiao
Keyword(s):  
Stainless Steel ◽  
Metal Forming ◽  
Material Flow ◽  
Elevated Temperatures ◽  
304 Stainless Steel ◽  
Electrical Heater ◽  
Backward Extrusion ◽  
Water Based ◽  
Inner Diameter ◽  
The One

A metal forming system comprising an electrical heater, capable of conducting processes at elevated temperatures, was developed to perform micro backward extrusion processes of SUS 304 stainless steel. Two punches with diameters of 1.6 mm and 1.8 mm were used to extrude the billets inside the die with an inner diameter of 2 mm. All processes were lubricated with water-based graphite and conducted under isothermal conditions at 400 °C. The results show that the developed extrusion system can be used to produce the stainless steel components with a micro cup-shaped profile. Moreover, the variation in the rim height of the cups produced by the 1.8 mm diameter punch is greater than the one by the 1.6 mm diameter punch. The results show that a decrease in the clearance between the punch and die could lead to an increase in the inhomogeneity of material flow in the micro backward extrusion processes.

Effect of Water on the IR Properties of Mg2+ Intercalated Electrochromic Nb2O5 Thin Films

2006 ◽  
Vol 972 ◽  
Author(s):  
Gargi Agarwal ◽  
G B Reddy
Keyword(s):  
Thin Films ◽  
Aqueous Solution ◽  
Water Content ◽  
Current Density ◽  
Sol Gel ◽  
Constant Current ◽  
Cyclic Stability ◽  
Constant Current Density ◽  
Effect Of Water ◽  
Ftir Studies

AbstractSol-gel derived Nb2O5 thin films were intercalated with Mg2+,using the non-aqueous solution of Mg(ClO4)2 in propylene carbonate (pc) as the electrolyte. 2% and 4% ( volume %) water was added to the electrolyte to study the effect of water on the electrochromic properties of Nb2O5. This paper presents the changes in optical and structural properties of the intercalated films with and without water in the electrolyte. The ratio (x) of the Mg2+ and Nb atoms has been controlled by optimizing the intercalation duration under a constant current density. The fall in transmittance on intercalation (for x= 0.8) increased by 15% with 4% water in the electrolyte, compared to the film intercalated without water. FTIR studies show that water is incorporated in the films on intercalation and small quantities of Mg(OH)2 and Nb-OH are formed along with Mg-O-Nb bonds. The presence of water in electrolyte decreases water content in the films and enhances the formation of Mg(OH)2, Mg-O-Nb and Nb-OH bonds. The recovery of Mg2+ on deintercalation is slightly reduced in presence of water in the electrolyte. The cyclic stability of the films intercalated without water is more than that of the films intercalated in presence of water.

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