• Proceedings of the Materials Research Society of Korea Conference
• /
• 2005.05a
• /
• pp.252-252
• /
• 2005

• Transactions on Electrical and Electronic Materials
• /
• v.12 no.4
• /
• pp.164-168
• /
• 2011

Nanocrystalline cadmium sulphide (CdS) thin films were prepared using chemical bath deposition (CBD), and the structural, optical and photoconductive properties were investigated. The crystal structure of CdS thin film was studied by X-ray diffraction. The crystallite size, dislocation density and lattice constant of CBD CdS thin films were investigated. The dislocation density of CdS thin films initially decreases with increasing film thickness, and it is nearly constant over the thickness of 2,500 ${\AA}$. The dislocation density decreases with increasing the crystallite size. The Urbach energies of CdS thin films are obtained by fitting the optical absorption coefficient. The optical band gap of CdS thin films increases and finally saturates with increasing the lattice constant. The Urbach energy and optical band gap of the 2,900 A-thick CdS thin film prepared for 60 minutes are 0.24 eV and 2.83 eV, respectively. The activation energies of the 2,900 ${\AA}$-thick CdS thin film at low and high temperature regions were 14 meV and 31 meV, respectively. It is considered that these activation energies correspond to donor levels associated with shallow traps or surface states of CdS thin film. Also, the value of ${\gamma}$ was obtained from the light transfer characteristic of CdS thin film. The value of ${\gamma}$ for the 2,900 A-thick CdS thin film was 1 at 10 V, and it saturates with increasing the applied voltage.

• Structural Engineering and Mechanics
• /
• v.67 no.3
• /
• pp.277-281
• /
• 2018

The analytical solution of two functionally graded layers with Volterra type screw dislocation is investigated under anti-plane shear impact loading. The energy dissipation of FGM layers is modeled by viscous damping and the properties of the materials are assumed to change exponentially along the thickness of the layers. In this study, the rate of gradual change ofshear moduli, mass density and damping constant are assumed to be same. At first, the stress fields in the interface of the FGM layers are derived by using a single dislocation. Then, by determining a distributed dislocation density on the crack surface and by using the Fourier and Laplace integral transforms, the problem are reduce to a system ofsingular integral equations with simple Cauchy kernel. The dynamic stress intensity factors are determined by numerical Laplace inversion and the distributed dislocation technique. Finally, various examples are provided to investigate the effects of the geometrical parameters, material properties, viscous damping and cracks configuration on the dynamic fracture behavior of the interacting cracks.

• Nuclear Engineering and Technology
• /
• v.3 no.1
• /
• pp.21-31
• /
• 1971

The part of the work of plastic deformation of metal goes into the changes in the total surface free energy. This contribution is dependent on the specific surface free energy, which is affected by the environment. Based on thermodynamical approach, volume constancy requirement and adsorption induced two distinct dislocation interaction mechanisms for strengthening or weakening of metals at surface, theoretical derivation has been made to show that the environmental contribution on the strain hardening, the stress and the energy required for plastic deformation can be expressed in terms of solid surface tension in vacuum (${\gamma}$$_{s}$), interfacial tension (${\gamma}$$_{se}$ ), surface dislocation density ($\rho$$_{s}$), internal dislocation density ($\rho$$_{i}$) and fraction of surface site uncoverage (f). On the basis of theoretical derivation, the various mechanical behaviours under different environments are predicted.d.d.

• Journal of the Korean Society for Heat Treatment
• /
• v.23 no.3
• /
• pp.131-136
• /
• 2010

The LCF (low cycle fatigue) behavior and the serration phenomena in the plastically deformed and non-deformed 5052 Al alloy were investigated. The plastic deformation was performed by 1 pass or 4 passes in ECAP (equal channel angular pressing) followed by annealing. Only cyclic hardening continued from the beginning until fracture at all strain amplitudes during LCF in the non-deformed alloy, which was caused by the increase in dislocation density during fatigue. Slight cyclic hardening followed by plateau until fracture was observed during LCF in the ECAPed alloy, which was caused by the slight increase in dislocation density in the beginning and then keeping constant in dislocation density afterward until fracture by forming subgrains in this stage of fatigue. The serrations on the stress-strain curves of this alloy were observed, which indicate that the dynamic strain aging (DSA) is occurring during plastic deformation. The variation in amplitudes of serration was studied by changing the strain rate in tensile or fatigue tests.

• Advances in materials Research
• /
• v.4 no.1
• /
• pp.1-12
• /
• 2015

Low carbon steel of composition 0.05C - 0.18 Mn - 0.012 Si is intercritically annealed at temperatures $750^{\circ}C$, $775^{\circ}C$ and $800^{\circ}C$. The equilibrated alloys of different amounts of austenite with varying carbon contents are quenched in iced water. The same alloys are subcritically annealed at $675^{\circ}C$ and $700^{\circ}C$ for varying periods of times; the subcritically annealed alloy samples are quenched in iced water. Optical, scanning electron and transmission electron microscopy are carried out for all the samples. The dislocation structure, its distribution and density present in the above prepared duplex ferrite martensite steels are studied. The martensites are found to be highly dislocated due to lattice invariant deformation. At the same time ferrite adjoining the martensite areas also exhibits quite a high dislocation density. The high dislocation density is favorable for strain ageing and hence bakes hardenability. EDS analyses were carried out for both martensite and ferrite phases; it is found that the degree of supersaturation in ferrite together with carbon content in martensite varies with the process parameters. The microhardness test results show that the hardness values of different phases differ appreciably with process parameters. The microstructures and the corresponding microanalyses reveal that differently processed steels contain phases of varying compositions and different distribution.

• Transactions of Materials Processing
• /
• v.30 no.5
• /
• pp.226-235
• /
• 2021

The strain aging behavior of a low carbon dual phase steel was examined in two conditions: representing room temperature strain aging (100 ℃ × 1 hr after 7.5 % prestrain) and bake hardening process (170 ℃ × 20 min after 2 % prestrain), basing on carbon effective diffusion and dislocation distribution. The first principle calculations revealed that (Mn or Cr)-vacancy-C complexes exhibit the strongest attractive interaction compared to other complexes, therefore, act as strong trapping sites for carbon. For room temperature strain aging condition, the carbon effective diffusion distance is smaller than the dislocation distance in the high dislocation density region near ferrite/martensite interfaces as well as ferrite interior considering the carbon trapping effect of the (Mn or Cr)-vacancy-C complexes, implying ineffective Cottrell atmosphere formation. Under bake hardening condition, the carbon effective diffusion distance is larger compared to the dislocation distance in both regions. Therefore, formation of the Cottrell atmosphere is relatively easy resulting in to a relatively large increase in yield strength under bake hardening condition.

• Korean Journal of Materials Research
• /
• v.20 no.1
• /
• pp.7-11
• /
• 2010

Yttria stabilized zirconia (Y-CSZ) single crystals show plastic deformation at high temperatures by activating dislocations. The effect of strain rate on the plastic behavior of this crystal was studied. As increasing strain rate from $\varepsilon=1.04\times10^{-5} sec^{-1}$ to $2.08\times10^{-5} sec^{-1}$ the yield drop was suppressed and resulted in higher Young's modulus and yield stress. Dislocation structures of the strained crystals were analyzed using a transmission electron microscope to elucidate the plastic behavior of these crystals. In the early stage of plastic deformation, dislocation dipoles and prismatic dislocation loops were formed in both samples. However, dislocation density was increased by increasing strain rate. Strong sessile dislocations were observed in the sample with higher strain rate, which may cause the higher work hardening.

• Journal of Ocean Engineering and Technology
• /
• v.4 no.2
• /
• pp.262-262
• /
• 1990

In order to check the effect of dislocation behavior on creep rate in 12% Chromium steel, 14 samples of different compositions were examined by creep rupture test, and subgrain sizes, distribution of dislocations and precipitates were checked. And, authors reviewed the behaviors of dislocations, the formation and growth of subgrains and precipitates during creep. The results are as the following: 1) Creep rates calculated by .epsilon. over dot = .rho.bv show 10-15% higher values than actual data measured. However, authors conclude that the density and velocity of dislocations together with subgrain size are important factors governing deformation during creep in 12% chromium steel. 2) The values of the strength of obstacles in the mobility of dislocations are more clearly depended on the effective stress in the range of $10{\pm}5kgf/mm^{2}$ and increase with the increase of temperature. 3) Creep rates decrease with the smaller sizes of subgrains formed and can result in the longer creep rupture lives(hours). The smaller subgrains can be made by forming shorter free gliding distances of dislocations with very fine precipitates formed in the matrix during creep by applying proper alloy design. 4) Dislocation mobility gets hindered by precipitates occurring, which are coarsened by the softening process governed by diffusion during long time creep.

• Journal of Ocean Engineering and Technology
• /
• v.4 no.2
• /
• pp.112-120
• /
• 1990

In order to check the effect of dislocation behavior on creep rate in 12% Chromium steel, 14 samples of different compositions were examined by creep rupture test, and subgrain sizes, distribution of dislocations and precipitates were checked. And, authors reviewed the behaviors of dislocations, the formation and growth of subgrains and precipitates during creep. The results are as the following: 1) Creep rates calculated by .epsilon. over dot = .rho.bv show 10-15% higher values than actual data measured. However, authors conclude that the density and velocity of dislocations together with subgrain size are important factors governing deformation during creep in 12% chromium steel. 2) The values of the strength of obstacles in the mobility of dislocations are more clearly depended on the effective stress in the range of $10{\pm}5kgf/mm^{2}$ and increase with the increase of temperature. 3) Creep rates decrease with the smaller sizes of subgrains formed and can result in the longer creep rupture lives(hours). The smaller subgrains can be made by forming shorter free gliding distances of dislocations with very fine precipitates formed in the matrix during creep by applying proper alloy design. 4) Dislocation mobility gets hindered by precipitates occurring, which are coarsened by the softening process governed by diffusion during long time creep.