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Dettagli della rivista
Formato
Rivista
eISSN
2083-4799
Pubblicato per la prima volta
23 Sep 2008
Periodo di pubblicazione
4 volte all'anno
Lingue
Inglese

Cerca

Volume 20 (2020): Edizione 4 (December 2020)

Dettagli della rivista
Formato
Rivista
eISSN
2083-4799
Pubblicato per la prima volta
23 Sep 2008
Periodo di pubblicazione
4 volte all'anno
Lingue
Inglese

Cerca

6 Articoli
Accesso libero

Experimental Analysis of Single Point Incremental Forming of Truncated Cones in DC04 Steel Sheet

Pubblicato online: 31 Dec 2020
Pagine: 5 - 15

Astratto

Abstract

Experimental tests to form truncated cones were carried out on a 3-axis milling machine. 0.8-mm thick low-alloy DC04 steel sheets were used as test material. The profile tool-path trajectory was generated using the EDGECAM software. The slope angle and diameter of the base of the conical shaped drawpieces were 70°-72° and 65 mm, respectively. The drawpiece heights were up to 75 mm. The full synthetic lubricant 75W85 was used to reduce the frictional resistance. The effect of selected incremental forming parameters on the formability of the DC04 sheet and the susceptibility to crack formation have been analysed and discussed. It was found that the surface roughness of the workpiece is strongly influenced by step depth. By controlling the feed rate, it is possible to prevent failure of the material.

Parole chiave

  • FEM
  • incremental forming
  • numerical modeling
  • SPIF
  • truncated cone
Accesso libero

Effect of Different Sized Multi Walled Carbon Nanotubes on the Barrier Potential and Trap Concentration of Malachite Green Dye Based Organic Device

Pubblicato online: 31 Dec 2020
Pagine: 16 - 26

Astratto

Abstract

Present work shows effect of 8 nm diameter and 30 nm diameter multi walled carbon nanotubes (MWCNT) on the barrier potential and trap concentration of Malachite Green (MG) dye based organic device. MWCNTs are basically a bundle of concentric single-walled carbon nanotubes with different diameters. In this work, ITO coated glass substrate and aluminium have been used as front electrode and back electrode respectively and the spin coating method is used to prepare the MG dye based organic device. It has been observed that both barrier potential and trap concentration are in correlation. Estimation of both these parameters has been done from current-voltage characteristics of the device to estimate the trap energy and the barrier potential of the device. Device turn-on voltage or the transition voltage is also calculated by using current-voltage characteristics. In presence of 8 nm diameter MWCNT, the transition voltage is reduced from 3.9 V to 2.37 V, the barrier potential is lowered to 0.97 eV from 1.12 eV and the trap energy is lowered to 0.028 eV from 0.046 eV whereas incorporation of 30 nm diameter MWCNT shows reduction of transition voltage from 3.9 V to 2.71 V and a reduction of barrier potential and trap concentration from 1.12 eV to 1.03 eV and from 0.046 eV to 0.035 eV respectively. Presence of both 8 nm diameter and 30 nm diameter MWCNT lowers trap energy approximately to 39% and 24% respectively and lowers barrier potential approximately to 13% and 8% respectively. Estimation of barrier potential is also done by Norde method which shows lowering of the value from 0.88 eV to 0.79 eV and from 0.88 eV to 0.84 eV in presence of both 8 nm and 30 nm diameter multi walled carbon nanotubes respectively. Calculation of barrier potential from both the I-V characteristics and Norde method are in unison with each other. Indication of enhancement of charge flow in the device can be ascribed to the truncated values of barrier potential and trap energy.

Parole chiave

  • Barrier Potential
  • Malachite Green Dye
  • MWCNT
  • Transition Voltage
  • Trap Energy
Accesso libero

Influence of Stick Electrode Coating’s Moisture Content on the Diffusible Hydrogen in Underwater Wet Shielded Metal Arc Welding

Pubblicato online: 31 Dec 2020
Pagine: 27 - 37

Astratto

Abstract

In shielded metal arc welding, the major factors influencing hydrogen uptake into the weld metal are (i) the hydrogen content of the base metal, (ii) hydrogen input by the welding consumable, and (iii) the hydrogen introduced by the atmosphere surrounding the arc process. In this study, the relative contribution of these factors is investigated and compared to each other for the case of underwater wet shielded metal arc welding. To assess the influence of the stick electrode’s moisture (capillary introduced water during handling operations) on the diffusible hydrogen in wet welded samples, wet and dry electrodes were welded at four different water depths. The moisture was absorbed through the sharpened electrode tip only, to ensure close to service conditions. The results show that the moist stick electrode coatings lead to 22.6% higher average diffusible hydrogen content in the weld metal (0.5 m water depth an average). However, the effect disappears with increasing water depths (no difference in 60 m water depth).

Parole chiave

  • Underwater wet welding
  • SMAW
  • diffusible hydrogen
  • water depth
  • electrode coating moisture
Accesso libero

Metallurgical Characterization and Kinetics of Borided 34CrNiMo6 Steel

Pubblicato online: 31 Dec 2020
Pagine: 38 - 48

Astratto

Abstract

Boriding of 34CrNiMo6 steel was performed in a solid medium consisting of Ekabor-II powders at 1123, 1173 and 1223 K for 2, 4 and 6 h. Morphological and kinetic examinations of the boride layers were carried out by optical microscopy, scanning electron microscopy (SEM) and X-ray diffraction (XRD). The thicknesses of the boride layers ranged from 22±2.3 to 145±4.1 depending on boriding temperature and time. The hardness of boride layer was about 1857 HV0.1 after boriding for 6 h at 1223 K, while the hardness of the substrate was only around 238 HV0.1. Growth rate constants were found to be between 1.2×10−13 – 9.8×10−13 m2/s depending on temperature. The activation energy for boron diffusion was estimated as 239.4±8.6 kJ mol−1. This value was comparable to the activation energies reported for medium carbon steels in the literature.

Parole chiave

  • Boriding
  • 34CrNiMo6 steels
  • boride layer
  • Ekabor II
  • growth rate constants
  • activation energy
Accesso libero

EBSD Characterization of Bobbin Friction Stir Welding of AA6082-T6 Aluminium Alloy

Pubblicato online: 31 Dec 2020
Pagine: 49 - 74

Astratto

Abstract

Electron Backscatter Diffraction (EBSD) was used to determine microstructural evolution in AA6082-T6 welds processed by the Bobbin Friction Stir Welding (BFSW). This revealed details of grain-boundaries in different regions of the weld microstructure. Different polycrystalline transformations were observed through the weld texture. The Stirring Zone (SZ) underwent severe grain fragmentation and a uniform Dynamic Recrystallisation (DRX). The transition region experienced stored strain which changed the grain size and morphology via sub-grain-boundary transformations. Other observations were of micro-cracks, the presence of oxidization, and the presence of strain hardening associated with precipitates. Flow-arms in welds are caused by DRX processes including shear, and low and high angle grain boundaries. Welding variables affect internal flow which affects microstructural integrity. The shear deformation induced by the pin causes a non-uniform thermal and strain gradient across the weld region, leading to formation of mixed state transformation of grain morphologies through the polycrystalline structure. The grain boundary mapping represents the differences in DRX mechanism I different regions of the weld, elucidates by the consequences of the thermomechanical nature of the weld. The EBSD micrographs indicated that the localised stored strain at the boundary regions of the weld (e.g. flow-arms) has a more distinct effect in emergence of thermomechanical nonuniformities within the DRX microstructure.

Parole chiave

  • AA6082-T6 aluminium alloy
  • bobbin friction stir welding
  • EBSD
  • grain boundary
  • microstructure
Accesso libero

Welding Thermal Cycles of Joints Made of S1100QL Steel by Saw and Hybrid Plasma-Mag Processes

Pubblicato online: 31 Dec 2020
Pagine: 75 - 86

Astratto

Abstract

The aim of this article is to validate the method of conducting a multipoint temperature measurement in the area of welded joints as a tool for quality assessment of the joints in question. In order to establish a relationship between temperature readout at a given point, the value of heat input and the distance of the point form the weld axis, preliminary tests have been conducted on a set of padding welds. Correlation of measurement data analysis showed the high 0.99 level. In the second stage of the study, temperatures of joints welded with two different methods have been measured: the HPAW (Hybrid Plasma – Arc Welding) and classic SAW (Submerged Arc Welding) method. The obtained temperature curves reflect the intensity of heat input in a given welding process. When compared to thermal effects on metallographic specimens, the shapes of the curves show a potential for quality assessment of joints in production conditions. Estimating thermal effects with classic analytical methods proves imprecise with respect to advanced high-power welding processes. Monitoring temperature will allow to assess the quality of joints in the course of welding, which may be a remarkable factor in terms of limiting the HAZ (heat affected zone) tempering of joints made from MART steels (advanced high strength martensitic steel) – a phenomenon that exceedingly decreases the strength of the joints. The method for quality assessment of welded joints presented in this paper allows to extend the analysis of welding thermal conditions.

Parole chiave

  • MART
  • structural steel
  • hybrid welding
  • HPAW
  • SAW
  • heat input
  • welding thermal cycle
6 Articoli
Accesso libero

Experimental Analysis of Single Point Incremental Forming of Truncated Cones in DC04 Steel Sheet

Pubblicato online: 31 Dec 2020
Pagine: 5 - 15

Astratto

Abstract

Experimental tests to form truncated cones were carried out on a 3-axis milling machine. 0.8-mm thick low-alloy DC04 steel sheets were used as test material. The profile tool-path trajectory was generated using the EDGECAM software. The slope angle and diameter of the base of the conical shaped drawpieces were 70°-72° and 65 mm, respectively. The drawpiece heights were up to 75 mm. The full synthetic lubricant 75W85 was used to reduce the frictional resistance. The effect of selected incremental forming parameters on the formability of the DC04 sheet and the susceptibility to crack formation have been analysed and discussed. It was found that the surface roughness of the workpiece is strongly influenced by step depth. By controlling the feed rate, it is possible to prevent failure of the material.

Parole chiave

  • FEM
  • incremental forming
  • numerical modeling
  • SPIF
  • truncated cone
Accesso libero

Effect of Different Sized Multi Walled Carbon Nanotubes on the Barrier Potential and Trap Concentration of Malachite Green Dye Based Organic Device

Pubblicato online: 31 Dec 2020
Pagine: 16 - 26

Astratto

Abstract

Present work shows effect of 8 nm diameter and 30 nm diameter multi walled carbon nanotubes (MWCNT) on the barrier potential and trap concentration of Malachite Green (MG) dye based organic device. MWCNTs are basically a bundle of concentric single-walled carbon nanotubes with different diameters. In this work, ITO coated glass substrate and aluminium have been used as front electrode and back electrode respectively and the spin coating method is used to prepare the MG dye based organic device. It has been observed that both barrier potential and trap concentration are in correlation. Estimation of both these parameters has been done from current-voltage characteristics of the device to estimate the trap energy and the barrier potential of the device. Device turn-on voltage or the transition voltage is also calculated by using current-voltage characteristics. In presence of 8 nm diameter MWCNT, the transition voltage is reduced from 3.9 V to 2.37 V, the barrier potential is lowered to 0.97 eV from 1.12 eV and the trap energy is lowered to 0.028 eV from 0.046 eV whereas incorporation of 30 nm diameter MWCNT shows reduction of transition voltage from 3.9 V to 2.71 V and a reduction of barrier potential and trap concentration from 1.12 eV to 1.03 eV and from 0.046 eV to 0.035 eV respectively. Presence of both 8 nm diameter and 30 nm diameter MWCNT lowers trap energy approximately to 39% and 24% respectively and lowers barrier potential approximately to 13% and 8% respectively. Estimation of barrier potential is also done by Norde method which shows lowering of the value from 0.88 eV to 0.79 eV and from 0.88 eV to 0.84 eV in presence of both 8 nm and 30 nm diameter multi walled carbon nanotubes respectively. Calculation of barrier potential from both the I-V characteristics and Norde method are in unison with each other. Indication of enhancement of charge flow in the device can be ascribed to the truncated values of barrier potential and trap energy.

Parole chiave

  • Barrier Potential
  • Malachite Green Dye
  • MWCNT
  • Transition Voltage
  • Trap Energy
Accesso libero

Influence of Stick Electrode Coating’s Moisture Content on the Diffusible Hydrogen in Underwater Wet Shielded Metal Arc Welding

Pubblicato online: 31 Dec 2020
Pagine: 27 - 37

Astratto

Abstract

In shielded metal arc welding, the major factors influencing hydrogen uptake into the weld metal are (i) the hydrogen content of the base metal, (ii) hydrogen input by the welding consumable, and (iii) the hydrogen introduced by the atmosphere surrounding the arc process. In this study, the relative contribution of these factors is investigated and compared to each other for the case of underwater wet shielded metal arc welding. To assess the influence of the stick electrode’s moisture (capillary introduced water during handling operations) on the diffusible hydrogen in wet welded samples, wet and dry electrodes were welded at four different water depths. The moisture was absorbed through the sharpened electrode tip only, to ensure close to service conditions. The results show that the moist stick electrode coatings lead to 22.6% higher average diffusible hydrogen content in the weld metal (0.5 m water depth an average). However, the effect disappears with increasing water depths (no difference in 60 m water depth).

Parole chiave

  • Underwater wet welding
  • SMAW
  • diffusible hydrogen
  • water depth
  • electrode coating moisture
Accesso libero

Metallurgical Characterization and Kinetics of Borided 34CrNiMo6 Steel

Pubblicato online: 31 Dec 2020
Pagine: 38 - 48

Astratto

Abstract

Boriding of 34CrNiMo6 steel was performed in a solid medium consisting of Ekabor-II powders at 1123, 1173 and 1223 K for 2, 4 and 6 h. Morphological and kinetic examinations of the boride layers were carried out by optical microscopy, scanning electron microscopy (SEM) and X-ray diffraction (XRD). The thicknesses of the boride layers ranged from 22±2.3 to 145±4.1 depending on boriding temperature and time. The hardness of boride layer was about 1857 HV0.1 after boriding for 6 h at 1223 K, while the hardness of the substrate was only around 238 HV0.1. Growth rate constants were found to be between 1.2×10−13 – 9.8×10−13 m2/s depending on temperature. The activation energy for boron diffusion was estimated as 239.4±8.6 kJ mol−1. This value was comparable to the activation energies reported for medium carbon steels in the literature.

Parole chiave

  • Boriding
  • 34CrNiMo6 steels
  • boride layer
  • Ekabor II
  • growth rate constants
  • activation energy
Accesso libero

EBSD Characterization of Bobbin Friction Stir Welding of AA6082-T6 Aluminium Alloy

Pubblicato online: 31 Dec 2020
Pagine: 49 - 74

Astratto

Abstract

Electron Backscatter Diffraction (EBSD) was used to determine microstructural evolution in AA6082-T6 welds processed by the Bobbin Friction Stir Welding (BFSW). This revealed details of grain-boundaries in different regions of the weld microstructure. Different polycrystalline transformations were observed through the weld texture. The Stirring Zone (SZ) underwent severe grain fragmentation and a uniform Dynamic Recrystallisation (DRX). The transition region experienced stored strain which changed the grain size and morphology via sub-grain-boundary transformations. Other observations were of micro-cracks, the presence of oxidization, and the presence of strain hardening associated with precipitates. Flow-arms in welds are caused by DRX processes including shear, and low and high angle grain boundaries. Welding variables affect internal flow which affects microstructural integrity. The shear deformation induced by the pin causes a non-uniform thermal and strain gradient across the weld region, leading to formation of mixed state transformation of grain morphologies through the polycrystalline structure. The grain boundary mapping represents the differences in DRX mechanism I different regions of the weld, elucidates by the consequences of the thermomechanical nature of the weld. The EBSD micrographs indicated that the localised stored strain at the boundary regions of the weld (e.g. flow-arms) has a more distinct effect in emergence of thermomechanical nonuniformities within the DRX microstructure.

Parole chiave

  • AA6082-T6 aluminium alloy
  • bobbin friction stir welding
  • EBSD
  • grain boundary
  • microstructure
Accesso libero

Welding Thermal Cycles of Joints Made of S1100QL Steel by Saw and Hybrid Plasma-Mag Processes

Pubblicato online: 31 Dec 2020
Pagine: 75 - 86

Astratto

Abstract

The aim of this article is to validate the method of conducting a multipoint temperature measurement in the area of welded joints as a tool for quality assessment of the joints in question. In order to establish a relationship between temperature readout at a given point, the value of heat input and the distance of the point form the weld axis, preliminary tests have been conducted on a set of padding welds. Correlation of measurement data analysis showed the high 0.99 level. In the second stage of the study, temperatures of joints welded with two different methods have been measured: the HPAW (Hybrid Plasma – Arc Welding) and classic SAW (Submerged Arc Welding) method. The obtained temperature curves reflect the intensity of heat input in a given welding process. When compared to thermal effects on metallographic specimens, the shapes of the curves show a potential for quality assessment of joints in production conditions. Estimating thermal effects with classic analytical methods proves imprecise with respect to advanced high-power welding processes. Monitoring temperature will allow to assess the quality of joints in the course of welding, which may be a remarkable factor in terms of limiting the HAZ (heat affected zone) tempering of joints made from MART steels (advanced high strength martensitic steel) – a phenomenon that exceedingly decreases the strength of the joints. The method for quality assessment of welded joints presented in this paper allows to extend the analysis of welding thermal conditions.

Parole chiave

  • MART
  • structural steel
  • hybrid welding
  • HPAW
  • SAW
  • heat input
  • welding thermal cycle

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