• Journal of Welding and Joining
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• v.35 no.1
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• pp.9-15
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• 2017

IMicrostructure evolution and tensile property in the weld heat-affected zone (HAZ) of austenitic Fe-30Mn-9Al-0.9C lightweight steels were investigated. Five alloys with different V and Nb content were prepared by vacuum induction melting and hot rolling process. The HAZ samples were simulated by a Gleeble simulator with welding condition of 300kJ/cm heat input and HAZ peak temperatures of $1150^{\circ}C$ and $1250^{\circ}C$. Microstructures of base steels and HAZ samples were observed by scanning electron microscopy (SEM) and transmission electron microscopy (TEM), and their mechanical properties were evaluated by tensile tests. The addition of V and Nb formed fine V and/or Nb-rich carbides, and these carbides increased tensile and yield strength of base steels by grain refinement and precipitation hardening. During thermal cycle for HAZ simulation, the grain growth occurred and the ordered carbide (${\kappa}-carbide$) formed in the HAZs. The yield strength of HAZ samples (HAZ 1) simulated in $1150^{\circ}C$ peak temperature was higher as compared to the base steel due to the formation of ${\kappa}-carbide$, while the yield strength of the HAZ samples (HAZ 2) simulated in $1250^{\circ}C$ decreased as compared to HAZ 1 due to the excessive grain growth.

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.24 no.11
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• pp.870-875
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• 2011

The $(Na_{0.52}K_{0.44})(Nb_{0.9}Sb_{0.06})O_3-0.04dLiTaO_3$ (NKNS-LT) ceramics with various $Cu_2O$ concentration were prepared by the conventional solid state reaction method. The $Cu_2O$ content was varied in the range of 0.1~0.4 wt%. The effects of Cu on microstructure, crystallographic phase transition, and piezoelectric properties were investigated. The material with perovskite structure had a tetragonal phase (T1) when $Cu_2O$ concentration was less than 0.3 wt% and it transformed to another tetragonal phase (T2) when the $Cu_2O$ amount was greater than 0.3 wt%. The phase boundary between T1 and T2 phases appeared at around 0.3 wt% of $Cu_2O$ concentration. The piezoelectric properties were shown the maximum values at the composition of the phase boundary. The electro-mechanical coupling factor ($k_p$) was 0.42 and the piezoelectric charge constant ($d_{33}$) was 245 pC/N at the 0.3 wt% of $Cu_2O$ concentration.

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.24 no.8
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• pp.622-626
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• 2011

Lead-free piezoelectric ceramics with the composition of $(Na_{0.54}K_{0.46})_{0.96}Li_{0.04}(Nb_{1-0.10-x}Ta_{0.10}Sb_x)O_{3}$ (x= 0~8 mol%) were fabricated by nomal sintering at $1,090^{\circ}C$ for 5 h. the phase structure, microstructure and electrical properties were investigated with a emphasis on the influence of the Sb content. All samples exhibit a single perovskite phase over the whole compositional range. For the ceramics with x= 4 [mol%], two phase transitions are observed at $75^{\circ}C$ and $366^{\circ}C$, corresponding to the phase transitions of orthorhombic to tetragonal (To-t) and tetragonal to cubic (Tc), respectively. high electrical properties of $d_{33}$= 210.83 pC/N, kp= 40%, ${\varepsilon}_r$= 1,091.35, $\rho$= 4.54 g/$cm^2$ were obtained from the specimen with x= 4 [mol%], which suggests that the composition ceramics is a promising lead-free piezoelectric material.

• Korean Journal of Materials Research
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• v.15 no.7
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• pp.453-457
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• 2005

Piezoelectric properties of $Pb(Mn_{1/3}Nb_{2/3})O_3-PbZrO_3-PbTiO_3$ ceramics were investigated with $Al_2O_3$ content $(0.0-1.0 wt\%)$. The constituent phases, microstructure, electromechanical coupling factor, dielectric constant, piezoelectric charge and voltage constants were analyzed. Diffraction peaks for (002) and (200) planes were identified by X-ray diffractometer for all the specimens doped with $Al_2O_3$, indicating the MPB (morphotropic phase boundary) composition of tetragonal structures. The highest sintered density of $7.8 g/cm^3$ was obtained for $0.2wt\%\;Al_2O_3-doped$ specimen. Grain size increased by doping $Al_2O_3$ up to $0.3 wt\%$, and it decreased by more doping. Electromechanical coupling factor, dielectric constant, piezoelectric charge and voltage constants increased by doping $Al_2O_3$ up to $0.2wt\%$, and it decreased by more doping. This might result from the formation of oxygen vacancies due to defects in $O^{2-}$ ion sites and the substitution of $Al^{3+}$ ions.

• Journal of Ceramic Processing Research
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• v.13 no.spc2
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• pp.341-345
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• 2012

[Li0.055(K0.5Na0.5)0.945](Nb1-xTax)O3 (0.05 ≤ x ≤ 0.25) ceramics were prepared by the partial sol-gel (PSG) method to improve the microstructure homogeneity of Ta5+ ion and were compared to those prepared by the conventional mixed oxide (CMO) method. For the PSG method, Ta(OC2H5)5 was directly reacted with calcined [Li0.055(K0.5Na0.5)0.945]NbO3 powders and the specimens sintered at 1100 ℃ for 5 hrs showed a single phase with a perovskite structure. Compared to the specimens prepared by conventional mixed oxide powders, the relative ratio of tetragonal phase to orthorhombic phase of the sintered specimens prepared by Ta(OC2H5)5 was larger than that of the sintered specimens prepared by Ta2O5. The electromechanical coupling factor (kp), piezoelectric constant (d33) and dielectric constant (εr) of the sintered specimens were increased with Ta5+ content. These results could be attributed to the decrease of the orthorhombic-tetragonal polymorphic phase transition temperature (To-t), which could be evaluated by oxygen octahedral distortion. Strain of the sintered specimens prepared by the PSG method was higher than that of specimens prepared by the CMO method due to the increase of relative density. The effects of crystal structure on the strain characteristics of the specimens were also discussed.

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
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• v.12 no.1
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• pp.35-43
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• 1999

Microstructures and dielectric properties of (Sr$\_$1-x/Ca$\_$x/) TiO$_3$-0.006Nb$_2$O$\_$5/ (0.05$\leq$x$\leq$0.2) boundary layer ceramics were investigated. The samples fired in a reducing atmosphere(N$_2$) were painted on the surface with CuO paste for the subsequent grain boundary diffusion, and then annealed at 1100$^{\circ}C$ for 2 hrs. The metal oxide of CuO infiltrated by thermal diffusion from surface of sample presents continuously in not grain but only grain boundary, and makes up thin boundary phase. The SEM photo, and EDAX revealed that CuO was penetrated rapidly into the bulk along the grain boundaries during the annealing. The average grain sizes is continuously increased as the content of substitutional Ca is increased from 5[mol%] to 15[mol%], but the average grain size of the sample with content of 20[mol%] Ca is slightly decreased. In the samples with content of 10∼15[mol%] Ca, excellent dielectric properties were obtained as follows; dielectric constant <25000, dielectric loss <0.3[%], and capacitance change rate as a function of temperature <${\pm}$10[%], respectively. All samples in this study exhibited dielectric relaxation with frequency as a functior of the temperature.

• International Journal of Industrial Entomology and Biomaterials
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• v.3 no.2
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• pp.149-152
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• 2001

Effect of topical application with 10, 20 and 30 ${\mu}g$/ml testosterone propionate and estradiol -17${\beta}$ on the fourth and fifth instar bivoltine NB18 silkworm larvae Bombyx mori, on the glycogen and protein contents of the Fat body and trehalose and protein contents of the haemolymph has been studied. Glycogen content of the fat body was significantly decreased in both testosterone propionate and estradiol -17${\beta}$ treatment groups except in the group treated with 30 ${\mu}g$ testosterone propionate where the increase was not significant when compared with those of carrier controls. The increase/decrease in haemolymph trehalose content did not show any significant difference in all the treated groups. Protein content of the fat body significantly increased in 10 and 20 mg testosterone propionate and estradiol -l7${\beta}$ treated groups but in 30 mg treated groups the increase was not significant when compared with those of carrier controls. There was no significant change in the haemolymph protein content in all the testosterone propionate and estradiol -17${\beta}$ treated groups except in group treated with 10 ${\mu}g$ estradiol -17${\beta}$ where it showed a significant decrease when compared with that of carrier control.

• Korean Journal of Materials Research
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• v.14 no.7
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• pp.462-469
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• 2004

The effect of Cu addition on the corrosion characteristics of Zr alloys that developed for nuclear fuel cladding in KAERI (Korea Atomic Energy Research Institute) was evaluated. The alloys having different element of Nb, Sn, Fe, Cr and Cu were manufactured and the corrosion tests of the alloys were performed in static autoclave at $360^{\circ}C$, distilled water condition. The alloys were also examined for their microstructures using the optical microscope and the TEM equipped with EDS and the oxide property was characterized by using X-ray diffraction. From the result of corrosion test more than 450 days, the corrosion rate of the Zr-based alloys was changed with alloying element such as Nb, Sn, Fe, Cr and especially affected by Cu addition. The corrosion resistance was increased with increasing the Cu content and the tetragonal $ZrO_2$ layer was more stabilized on the Cu-containing alloys.

• Korean Journal of Metals and Materials
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• v.50 no.2
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• pp.183-190
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• 2012

Hydrogen was generated by the reaction of metal hydride with water. The variation of hydrogen generation with the kind of powders (milled $MgH_2$, and $MgH_2$ milled with various contents of MgO, $MgCl_2$ or $Ni+Nb_2O_5$) was investigated. $MgH_2$ powder with a hydrogen content of 6.05 wt% from Aldrich Company was used. Hydrogen is generated by the reaction of Mg as well as $MgH_2$ with water, resulting in the formation of byproduct $Mg(OH)_2$. For about 5 min of reaction time, milled $95%MgH_2+5%MgO$ has the highest hydrogen generation rate among milled $MgH_2+x%MgO$ (x=0, 5, 10, 15 and 20) samples. Milled $90%MgH_2+10%MgCl_2$ has the highest hydrogen generation rate among all the samples.

• Nuclear Engineering and Technology
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• v.51 no.3
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• pp.776-783
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• 2019

Laser welding is usually a more effective method than electron-beam one since a vacuum chamber is not required. It is important for joining Zr-1%Nb (E110) alloy in a manufacturing process of nuclear fuel rods. In the present work, effect of energy parameters of pulsed laser welding on properties of butt joints of sheets with a thickness of 0.5 mm is investigated. The most efficient combination has been found (8-11 J pulse energy, 10-14 ms pulse duration, 780-810 W peak pulse power, 3 Hz pulse frequency, 1.12 mm/s welding speed). The results show that ultimate strength under static loading can not be used as a quality criterion for zirconium alloys welds. Increased shielding gas flow rate does not allow to protect weld metal totally and contributes to defect formation without using special nozzles. Several types of imperfections of the welds have been found, but the major problem is branching microcracks on the surface of the welds. It is difficult to identify the cause of their appearance without additional research on improving the welding zone protection (gas composition and flow rate as well as nozzle configuration) and studying the hydrogen content in the welds.