• Korean Journal of Materials Research
• /
• v.10 no.9
• /
• pp.624-628
• /
• 2000

As a power durable-electrode in SAW filter, Al-1%Cu/tungsten nitride multi-layer thin film was fabricated by magnetron sputtering process. Tungsten nitride films had the amorphous phase at the nitrogen ratio, R, ranging from 10~40%. The amorphization could be controlled by nitrogen ratio, R= $N_2$/($N_2$+Ar) as a sputtering process parameter. Residual stress in tungsten nitride abruptly decreased with the formation of amorphous phase. Al-1%Cu thin film was deposited on the amorphous tungsten nitride. After the multi-layed thin film was annealed for 4 hours at 453K, the resistivity decreased as $3.6{\mu}{\Omega}-cm$, which was due to grain growth reduced crystal defects.

• The Journal of Korean Institute of Communications and Information Sciences
• /
• v.18 no.8
• /
• pp.1102-1107
• /
• 1993

Microwave dielectric properties of CaTiO3 and CaTiO3-TiO2 ceramics for the composition range between 40 and 50 mol% CaO in CaO-TiO2 binary system were investigated. CaTiO3 ceramics with50 mol% CaO showed the dielectric constant (e,) of 178, the temperature coefficient of resonant frequency(c,) of+1000 ppm/'c and the qualify factor Q of 2760 (f0=2.7 GHz ). Dielectric constant and temperature coefficient of resonant frequency of ceramics with dual phases of CaTiO3 and TiO2 decreased gradually from those of CaTiO3 as the CaO content decreased. Q value and density were found to have minimum at the composition of 47 mol% CaO. The degradation of Q value and density in dual phase ceramics seems to be caused by the large pores at grain boundaries and/or within grains remained after rapid growth of CaTiO3 grains as TiO2 Phase decreased.

• Korean Journal of Materials Research
• /
• v.5 no.1
• /
• pp.132-139
• /
• 1995

Tnermomechanical treatment consisting of homogenizing, hot and warm rolling were introduced to Al-MgCu-Mn alloys for obtaining superplasticity. The factors affecting the superplasticity of the alloys were investigated by optical and transmission electron microscopy. Large particles which had not been decomposed during homogenizing treatments remained stable in the hot and warm rolling processes. These particles were a source of cavitation and poor elongation in superplastic deformation. On the other hand, fine precipitates were produced during thermomechanical processing, and resulted in improvement of superplasticity by stabilizing microstructure. Two-step homogenizing and air cooling process was more effective than onestep homogenizing and furance cooling process in removing microsegregations and producing fine particles.

• Journal of the Korean Magnetics Society
• /
• v.4 no.3
• /
• pp.233-238
• /
• 1994

The effect of die upset and heat treatment on the magnetic properties of mechanically ground $Nd_{16}Fe_{78}B_{6}$ alloys has been studied. Although stripe domain patterns parallel to the compression direction were observed after die upset, it was found that crystallographic c-axes of a specimen were not completely aligned along the compression direction' which resulted in the decrease of Br. The average grain size of a die-upset specimen annealed for 5 hours at $1000^{\circ}C$ was about $20\mu\textrm{m}$, resulting in reduced values of Br and $_{i}H_{c}$. The maximum magnetic properties (Br=7.8 kG and $(_{i}H_{c}=14\;kOe) were obtained from the magnet die-upset at $750^{\circ}C$ using the alloy powder ground for 13 hours.

• Journal of Korea Foundry Society
• /
• v.31 no.6
• /
• pp.347-353
• /
• 2011

There is thixo-extrusion to form high strength aluminum alloy. But, it is a problem that grains become grain coarsening during reheating process because the alloy was exposed at high temperature. In order to solve grain growth during reheating process, calcium was added in Al-Zn-Mg alloys. Primary a grain sizes of semi-solid Al-Zn-Mg-(0, 0.4, 0.6 and 0.9, wt.%)Ca were measured with image analyzer after reheating. Measured primary a grain sizes were applied to LSW(Lifshitz-Slyozov and Wagner) equation to check the effect of Ca on grain coarsening. Coarsening rate constant K values of semi-solid Al-Zn-Mg-(0, 0.4, 0.6 and 0.9, wt.%)Ca alloys were $371\;mm^3s^{-1}$, $247\;mm^3s^{-1}$, $198\;mm^3s^{-1}$ and $166 mm^3s^{-1}$, respectively. As increasing calcium content, K value decreased which means grains are refined. Also, grains of calcium addition were more spherical than that of calcium free.

• Journal of the Korean Society for Heat Treatment
• /
• v.11 no.4
• /
• pp.324-332
• /
• 1998

The grain growth characteristics of dual-phase (${\alpha}+{\gamma}$) containing high Cr-steel have investigate using ${\alpha}$-, ${\gamma}$-single phases and (${\alpha}+{\gamma}$)dual-phase of 12%Cr Steel. The heat treatment has performed at $1000-1200^{\circ}C$ for 1-100hr. The results are as follows : 1) The grain growth rate in (${\alpha}+{\gamma}$) dual phase was substantially slower than that of single grain. 2) The relation between mean grain radius $\bar{{\gamma}}$ and annealing time t is, in general, described as following equation : $$(\bar{{\gamma}})^n-(\bar{{\gamma}_o})^n=K_n{\cdot}t{\cdots}{\cdots}(1)$$ i) In the case of single phase of high Cr steel, Eq.(1) is described as $(\bar{{\gamma}})^2-(\bar{{\gamma}_o})^2=K_2{\cdot}t$ and the grain growth is controlled by boundary migration. ii) In dual phase, the grain growth needs diffusion of alloying elements because the chemical composition of ${\alpha}$- and ${\gamma}$- phases differs from each other. When the volume fraction of ${\alpha}$-, ${\gamma}$-phase was almost equal and ${\gamma}$-phase in the case of 80 and $90%{\gamma}$. Eq.(1) is described as $(\bar{{\gamma}})^3-(\bar{{\gamma}_o})^3=K_3{\cdot}t$ because the grain growth is controlled by volume diffusion iii) In the case of ${\gamma}$-rich phase (80 and $90%{\gamma}$), the grain growth of minor phase (10 and $20%{\alpha}$) is described as $(\bar{{\gamma}})^4-(\bar{{\gamma}_o})^4=K_4{\cdot}t$ because the boundary diffusion is predominent rather than volume diffusion.

• Journal of the Korean Society for Heat Treatment
• /
• v.21 no.6
• /
• pp.293-299
• /
• 2008

In order to provide with fundamental data of the wrought Mg alloy for press forging, the effect of annealing temperature on the microstructure, texture development and tensile properties is studied in a commercial AZ31B Mg alloy sheet. Basal texture i.e. $(0001){\pm}5^{\circ}$[21$\bar{3}$0] is developed in a commercial AZ31B Mg sheet, and the texture is not changed considerably by annealing over $400^{\circ}C{\times}30min$, while (10$\bar{3}$0) component with high intensity can be observed due to abnormal grain growth. When the sheet is tensile-deformed with RD, $45^{\circ}$ and TD directions at room temperature, fracture strains are given by 25.8, 21.4 and 11.9% in the order of RD, $45^{\circ}$ and TD directions, respectively. With increasing annealing temperature up to $450^{\circ}C{\times}30min$, little change in mean grain size can be revealed by annealing below $300^{\circ}C{\times}30min$ but an abnormal grain growth, where some grains become significantly coarser than the rest, occurs by annealing above $400^{\circ}C{\times}30min$. The maximum tensile strain of around 25% is obtained by annealing below $300^{\circ}C{\times}30min$, but it is abruptly decreased to 16% by annealing above $400^{\circ}C{\times}30min$ owing to intergranular fracture of abnormal grown grains.

• Applied Chemistry for Engineering
• /
• v.9 no.4
• /
• pp.481-485
• /
• 1998

Hydrated aluminum sulfate, an inorganic polymer, was synthesized from kaolin in $H_2SO_4$ solution using microwave energy. The maximum rates of alumina extracted from calcined kaolin were 72.8% in a conventional process ($80^{\circ}C$, 1M, and 180min) and 99.9% in a microwave process ($90^{\circ}C$, 1M, and 60 min). Compared with the conventional one, the hydrated aluminum sulfate synthesized under the microwave process had layer structure consisting of plate-shaped large grains. After synthesis and then calcination at $1100^{\circ}C$, both products on conventional and microwave processes were ${\gamma}-Al_2O_3$ with agglomerated powders of spherical shape. The specific area of the products in conventional and microwave processes were 113.5 and $106.6m^2/g$, and their average grain sizes were 46.5 an $26.3{\mu}m$, respectively.

• Journal of Welding and Joining
• /
• v.34 no.6
• /
• pp.55-61
• /
• 2016

Recently developed ferritic heat resistance steel, T24 was used to evaluate microstructure characteristics of simulated heat affected zone. Also, correlation between the prior austenite grain size and amount of $M_{23}C_6$ carbide dissolution was discussed. With the increasing of peak temperature, Grain size steadily increased up to $1050^{\circ}C$ and then rapidly increased at $1150^{\circ}C$. Of the peak temperature $950{\sim}1050^{\circ}C$, amounts of $M_{23}C_6$carbide dissolution are low. But Most of $M_{23}C_6$ carbide that is inhibited grain growth were dissolved above $1050^{\circ}C$ and decreased volume fraction of carbide. This indicates that grain growth may be achieved through dissolution of carbide in the base material. As of welding, due to very rapid heating rate, $M_{23}C_6$ carbide exists above equilibrium solution temperature that is $800^{\circ}C$, even at $1050^{\circ}C$. So, It was confirmed that close correlation between carbide dissolution in the base material and grain growth. Calculated grain size has a linear relationship with peak temperature, on the other hand, measured grain size discontinuously increased between $950{\sim}1050^{\circ}C$ and above $1050^{\circ}C$. Grain size of heat affected zone at $1350^{\circ}C$ peak temperature showed maximum 67um and minimum 4um. Also, The number of side showed 3 to 10.

• Korean Journal of Materials Research
• /
• v.11 no.6
• /
• pp.483-491
• /
• 2001

The recovery and recrystallization behavior of cold-rolled Zr-based alloys during isothermal annealing at temperatures from $575^{\circ}C$ to $650^{\circ}C$ was studied by thermoelectric power and Vickers microhardness measurement. The recovery and recrystallization resulted in the increase of TEP doe to the extinction of lattice defect, vacancy, dislocation and stacking fault during isothermal annealing after cold- rolling. The completion of recrystallization could be determined much clearly by TEP behavior than by microhardness change in Zr-based alloys. Especially, the recovery and recrystallization were classified separately by TEP behavior in Zr-0.4Nb-xSn alloys. From the analysis of TEP behavior and microhardness, the addition of Sn caused to form the interaction between stain field and dislocation, which resulted in the delay of recovery in Zr-based alloys. The precipitation due the addition of Nb suppressed the grain growth after recrystallization effectively in Zr-based alloys.