• 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.14 no.1
• /
• pp.13-18
• /
• 2004

Titanium alloys are the one of promising candidate materials for medium high temperature parts in the aircraft, automobile, petrochemistry and electrochemistry because of their high strength with low density in medium high temperature. In this study, the effects of aging and heat treatments on the mechanical properties of Ti-15-3 alloy in medium high temperature, which was $400^{\circ}C$, were studied. Solid solution treatment was performed at $8000^{\circ}C$ of $\beta$ phase region for 1 h and the alloy was quenched in water. The alloy was aged at $5000^{\circ}C$ of $\alpha$ and $\beta$ two-phase region for 1, 2, 4, 8, ... and 100 h to increase the mechanical property. The $\beta$ single phase was observed at all parts of specimens in Ti-15-3 alloy after ST. As the aging at $500^{\circ}C$, fine precipitates of a phase was generated from matrix of $\beta$ phase and the microstructure was consisted of weaving structure such as Widmanstiitten a phase. The most suitable aging time is 24h in$ 400^{\circ}C$. At this time, strength is 1164 MPa and elongation is about 12%. In room temperature, elongation of Ti-15-3 alloy aged at $500^{\circ}C$ for 16 h is poor (=3%) in spite of high tensile strength (1458 MPa).

• Journal of the Korean Ceramic Society
• /
• v.34 no.12
• /
• pp.1254-1260
• /
• 1997

Influence of applied electric field on the low temperature degradation of 3 mol% YaO3 stabilized tetragonal zirconia polycrystals(3Y-TZP) was investigated using X-ray diffractometry of specimens aged under the dc field of 1.1 kV/mm in silicone oil both of 12$0^{\circ}C$-21$0^{\circ}C$. After the aging, the tetragonal to monoclinic phase transformation was observed only on the specimen surface of 3Y-TZP faced to the anode. This indicated that the surface was overcrowded with oxygen ions as a result of diffusion of oxygen vacancies toward the cathode-sided surface. To elucidate an influence of the applying time of the electric field on the extent of the degradation of 3Y-TZP in air, specimens were aged fore 0-2 hours under the electric field in the oil bath of 12$0^{\circ}C$ and then subsequently aged for 3h at 22$0^{\circ}C$ in air. The longer the specimens were aged under the field, the more extensive the transformation to the monoclinic phase was on the specimen surface faced to the cathode, probably originated from a high diffusion rate of oxygen ions due to a steep oxygen vacancy concentration gradient.

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
• /
• v.20 no.10
• /
• pp.873-877
• /
• 2007

In order to apply a complex multilayer chip LC filter, this study has estimated the interfacial reaction and coupling properties of dielectric materials $Pb(Fe_{1/2}Nb_{1/2})O_3$ and Ni-Zn-Cu ferrite materials through low-temperature co-sintering (LTCS). PFN powders were fabricated using double calcinated at $700^{\circ}C$ and then $850^{\circ}C$. While the perovskite phase rate was found to be 91 %, after heat treatment at $900^{\circ}C$ for 6h, the perovskite phase rate and density exhibited a value of 100 % and 7.46$g/cm^3$, respectively. The PFN/Ni-Zn-Cu ferrite, PFN/CUO (or $Pb_2Fe_2O_5$) and ferrite/CuO (or $Pb_2Fe_2O_5$) were mechanically coupled through interfacial reactions after the specimen was co-sintered at $900^{\circ}C$ for 6 h. No intermediate layer exists for the mutual coupling reaction. This result indicates the possibility of low-temperature co-sintering without any interfacial reaction layer for a multilayer chip LC filter.

• Journal of the Korean Ceramic Society
• /
• v.30 no.1
• /
• pp.46-54
• /
• 1993

$\beta$-SiC was chemically vapor deposited by pyrolysis of MTS＋H2 gas mixture. The experiments were conducted in the temperature range of 1100~150$0^{\circ}C$ with a r.f. induction furnace under atmospheric pressure. The IR, XRD, EDS and AES analysis revealed that the free Si was always codeposited with SiC below 140$0^{\circ}C$, regardless of the total flow rate and MTS concentration, whereas $\beta$-SiC single phase was deposited at 150$0^{\circ}C$. C3H8 or CH2Cl2 as an excess C sources, was supplied with MTS in order to obtain stoichiometric SiC at low temperature. With the addition of C3H8 or CH2Cl2, the deposition rate was increased and $\beta$-SiC single phase could be deposited even at temperature as low as 110$0^{\circ}C$. In the absence of C3H8 or CH2Cl2, the microhardness of the layer was quite low (

• Journal of the Korean Institute of Electrical and Electronic Material Engineers
• /
• v.16 no.12S
• /
• pp.1200-1204
• /
• 2003

In this study, in order to develop the low temperature sintering ceramics for multi-layer piezoelectric transformer, PSN-PZT system ceramics were manufactured as a function of CuO addition and their dielectric and piezoelectric characteristics were Investigated. CuO addition facilitated densification at low temperature due to the effect of Cu$_2$O-PbO liquid phase. Through the X-ray diffraction pattern study, absence of second phase unwanted was confirmed. Among the specimen to which CuO was added, the 0.6wt% CuO added specimen sintered at 900$^{\circ}C$ and 920$^{\circ}C$ showed the most excellent mechanical quality factor and electromechanical coupling factor, respectively. Besides the densification accelerator, CuO acted as a accepter and increased mechanical quality. Compared with the specimen with no addition sintered at 1150$^{\circ}C$ , the 0.6wt% CuO added specimen sintered at 920$^{\circ}C$ showed the appropriate dielectric and piezoelectric characteristics for multi-layer piezoelectric transformer.

• Korean Journal of Metals and Materials
• /
• v.48 no.5
• /
• pp.449-455
• /
• 2010

To enhance the efficiency of dye sensitized solar cells, we proposed crystalline anatase-$TiO_{2}$ by using a low temperature process ($150^{\circ}C{\sim}250^{\circ}C$). We successfully fabricated 30 nm-$TiO_{2}$ at a fixed atomic layer deposition condition of 1.0 sec of TDMAT pulse, 20 sec of TDMAT purge, 0.5 sec of H$_{2}$O pulse, and 20 sec of H$_{2}$O purge. In order to examine the microstructure, phase, and band-gap of the TiO$_{2}$ respectively, we employed a Nano-Spec, transmission electron microscope, high resolution XRD, Auger electron spectroscopy, scanning probe microscope, and UV-VIS-NIR. We were able to fabricate a crystalline anatase-phase of 30 nm-TiO$_{2}$ successfully at temperatures above $180^{\circ}C$. Our results showed that our proposed low temperature ALD process (below $200^{\circ}C$) might be applicable to glass and flexible polymer substrates.

• Korean Journal of Microbiology
• /
• v.37 no.3
• /
• pp.228-233
• /
• 2001

The acid tolerance response (ATR) of log-phase Salmouella enterica seroyar Typhimurium is induced by acid adaptation below pH4.5 and will protect cells against more severe acid. Two distinctive ATR systems in thisorganism are a log-phase and stationary-phase ATR in which acid adaptations trigger the synthesis of acid shockproteins (ASPs). We found that log-phase ATR system was strongly affected by environmental factor, low tem-perature, $25^{\circ}C$. Exposure to low temperature and mild acid has been shown to increase acid survival dra-matically, and this survival rate was showed higher than $37^{\circ}C$. Especially unadapted cells at $25^{\circ}C$ presented tenthousand folds survival increasing when compared with cells at $37^{\circ}C$. The degree of acid tolerance of rpoSwhich is blown to be required for acid tolerance more increase than $37^{\circ}C$. Even though AIR pattern of rpoSbetween unadapted and adapted was showed similar at pH 3.1, rpoS-dependent ATR system also has beendetected in low temperature because rpoSAp prevents sustained acid survival at $25^{\circ}C$. Therefore the resultssuggest low temperature ATR system requires rpoS-dependent and -independent both. To investigate the basisfor low temperature related ATR system, gene that was participated for low temperature acid tolerance (lat) wasscreened in virulent S. enterica serovar Typhimurium UKl Using the technique of P22- MudJ (Km, lacZ)-directed lacZ operon fusion, LF452 latA‥‥MudJ was isolated. The latA‥‥MudJ of S. enterica Typhimurium pre-vented low temperature acid tolerance response. Therefore latA is considered one of the important genes for acidadaptation.

• Korean Journal of Materials Research
• /
• v.30 no.6
• /
• pp.315-320
• /
• 2020

This study deals with the yielding behavior and strain aging properties of three bake hardening steels with dual-phase microstructure, fabricated by varying the annealing temperature. Bake hardening and aging tests are performed to examine the correlation of martensite volume fraction with yielding behavior and strain aging properties of the bake hardening steels with dual-phase microstructure. The volume fraction of martensite increases with increasing annealing temperature. Room-temperature tensile test results show that the yielding behavior changes from discontinuous-type to continuous-type with increasing volume fraction of martensite due to higher mobile dislocation density. According to the bake hardening and aging tests, the specimen with the highest fraction of martensite exhibited high bake hardening with low aging index because solute carbon atoms in ferrite and martensite effectively diffuse to dislocations during the bake hardening test, while in the aging test they diffuse at only ferrite due to lower aging temperature.

• Nuclear Engineering and Technology
• /
• v.53 no.3
• /
• pp.833-841
• /
• 2021

During the postulated severe accident of nuclear reactor, eutectic reaction leads to low-temperature melting of fuel cladding and early failure of core structure. In order to model eutectic melting with the moving particle semi-implicit (MPS) method, the eutectic reaction model is developed to simulate the eutectic reaction phenomenon. The coupling of mass diffusion and phase diagram is applied to calculate the eutectic reaction with the uniform temperature. A heat transfer formula is proposed based on the phase diagram to handle the heat release or absorption during the process of eutectic reaction, and it can combine with mass diffusion and phase diagram to describe the eutectic reaction with temperature variation. The heat transfer formula is verified by the one-dimensional melting simulations and the predicted interface position agrees well with the theoretical solution. In order to verify the eutectic reaction models, the eutectic reaction of uranium and iron in two semi-infinite domains is simulated, and the profile of solid thickness decrease over time follows the parabolic law. The modified MPS method is applied to calculate Transient Reactor Test Facility (TREAT) experiment, the penetration rate in the simulations are agreeable with the experiment results. In addition, a hypothetical case based on the TREAT experiment is also conducted to validate the eutectic reaction with temperature variation, the results present continuity with the simulations of TREAT experiment. Thus the improved method is proved to be capable of simulating the eutectic reaction in the severe accident.