• Journal of the Korean Ceramic Society
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• v.37 no.5
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• pp.418-424
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• 2000

Effects of Ar ion damage prior to the phase transformation from pyrochlore to perovskite structure of PZT thin films have been investigated. As the degree of damage increased by increasing the acceleration voltage in the ion mass doping system, the phase transformation temperature decreased such that the temperature could be lowered down to 550$^{\circ}C$ when the film was damaged at 15 kV for 5 minutes. When the film was damaged prior to the heat treatment grain size of the perovskite thin films became less than 300${\AA}$. It turned out that relatively high value of the remanent polarization (about 30${\mu}$C/$\textrm{cm}^2$) as well as improvement of the fatigue characteristics to a large extent is closely related to the fine grain size of thus obtained PZT films.

• Proceedings of the Korean Society for Technology of Plasticity Conference
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• 2009.10a
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• pp.173-176
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• 2009

A great emphasis has been placed on the design of heat treatment process to achieve desired microstructure and mechanical property of final product. In this study, finite element analysis was carried out to predict temperature, microstructure and hardness of eutectoid steel after water quenching. Convective heat transfer coefficients were determined by inverse analysis using surface temperatures measured with three different installation methods of thermocouples. Finally, the effect of convective heat transfer coefficients on the prediction of temperature history and hardness was analyzed by comparing experimental and simulation results.

• Journal of the Korean Ceramic Society
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• v.25 no.3
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• pp.277-283
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• 1988

Extremely fine $TiO_2$ powders were synthesized from titanium chloride by the precipitation and freeze drying method. The phase transformation and electrical conductivity were investigated as a function of temperature. X-ray analysis showed that the phase transformation of the synthesized powder from the anatase to rutile occured at 64$0^{\circ}C$ and finished at 92$0^{\circ}C$ due to small particle size and large specific surface area. The activation energy obtained from electrical conductivity vs. temperature was about 1.63eV. This relatively large value was due to porosity in the specimen.

• Journal of Korea Foundry Society
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• v.11 no.5
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• pp.406-413
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• 1991

Ductile cast iron(DCI) with a multi-phase(ferrite-bainite-martensite) structures was produced by various special heat treatment. Intercritical heat treatment(I. C.), intermediate heat treatment(I. M.) and step quenching(S. Q.) were used to strengthen and toughen the fracture initiation sites such as graphite-marix interfaces and eutectic cell boundaries in DCI. The purpose of this study was to investigate of DCI by the special heat treatment. (I. C., I. M., and S. Q.) At a result, bainite nucleation rate at higher temperature was higher than that of at lower temperature, and shapes of bainite and martensite became bar /spheroidal type with increase of isothermal transformation time.

• Korean Journal of Materials Research
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• v.13 no.4
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• pp.224-227
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• 2003

The sliding wear behavior of a Fe-base hardfacing alloy was investigated in the temperature range of $25∼250^{\circ}C$ under a contact stress of 15 ksi (103 MPa). The wear loss of this Alloy in pressurized water was less than that of NOREM 02. And galling did not occurred at this alloy in all temperature ranges. It was considered that the wear resistance of this Alloy was attributed to the strain-induced phase transformation from austenite to $\alpha$'martensite during sliding wear.

• Journal of Powder Materials
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• v.17 no.3
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• pp.197-202
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• 2010

Low temperature degradation behavior in yttria stabilized tetragonal zirconia polycrystal (Y-TZP) ceramics was microscopically observed from the phase contrast between monoclinic surface and tetragonal matrix. The degradation behavior was dependent on the surface treatment of sintered Y-TZP, even if the sintering history is same. In the mirror polished specimen, the monoclinic layer appeared in a uniform thickness from the surface. On the contrary, for the specimen with coarse scratch, the thickness of degraded surface was more than double especially from the coarse scratch. Since the scratch results in local deformation, the residual stress should be induced around the scratch. With the transformation from tetragonal to monoclinic, the volume expansion exerts a stress on a neighboring grains and promotes a successive phase transformation. Such a autocatalytic effect can be triggered from the part of coarse scratch.

• Journal of Biomedical Engineering Research
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• v.14 no.3
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• pp.283-290
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• 1993

In thls study, the effects of the composltional change of cast Ni-Ti alloys on its characteristics including mechanical properties, phase transformation temperature, and ion releasing rate were investigated. brittle:behavior was shown in the stress-strain curve of the alloy containing low Ti content (Ni-44.0%Ti). By increasing the Ti content, the trend in stress-strain curves changed from that of superelasticity to that of shape memory effect(Ni-44.4%Ti, Ni-45.1%Ti, Ni-45, 5%Ti). Phase transformation temperature ($A_f, {\;}M_5$ point) increased with increasing the Ti content. lon releasing rate of four types of Mi-Ti alloys was very low compared to that of the dental commerical Ni-Cr alloy.

• The Korean Journal of Ceramics
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• v.1 no.1
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• pp.45-54
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• 1995

Four kinds of silicon nitride based ceramic materials have been hot pressed. Effect of the sintering additives on the phase transformation, microstructural development and mechanical properties was investigated. While sintering under the same condition a big difference among the microstructures of the specimens, they appeared alike if sintered to have a similiar $\alpha$-$\beta$ phase ratio. The specimen of the stoichiometric $\alpha$-$\beta$ sialon composition showed very limited amount of the intergranular glassy phase and a significant degree of the residual stress. It exhibited almost no strength degradation up to $1300^{\circ}C$, and the strength of the specimen degraded more as its composition deviated from the stoichiometry.

• Journal of Korean Vacuum Science & Technology
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• v.1 no.1
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• pp.24-29
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• 1997

Surface morphologies and fundamental characteristics of molybdenum nitride films deposited by reactive dc magnetron sputtering were studied for application to Cu diffusion barrier. A phase transformation from Mo to $\gamma$-Mo$_2$N phase at 0.5$N_2$ flow ratio.($N_2$/(Ar+$N_2$)) equal to and larger than 0.2, whereas a second phase transformation to $\gamma$-MoN phase at 0.5 N2 flow ratio, With the variation of the N2 ratio the surface morphologies of the films were generally smooth except the cases of 0.2 and 0.3$N_2$ gas rations, where build-up of film stresses occurred. $\gamma$-Mo$_2$N film was found to crystallize at the deposition temperature of 40$0^{\circ}C$. The surfaces of $\gamma$-Mo$_2$N films deposited up to 40$0^{\circ}C$ were smooth, but the film deposited at 50$0^{\circ}C$ had very rough surface morphology. It seems that this was due to the building-up of thermal stresses at the high deposition temperature, which might lead to hillock formation.

• Korean Journal of Materials Research
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• v.25 no.11
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• pp.577-582
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• 2015

The present study is concerned with the influence of niobium(Nb) addition and austenitizing temperature on the hardenability of low-carbon boron steels. The steel specimens were austenitized at different temperatures and cooled with different cooling rates using dilatometry; their microstructures and hardness were analyzed to estimate the hardenability. The addition of Nb hardly affected the transformation start and finish temperatures at lower austenitizing temperatures, whereas it significantly decreased the transformation finish temperature at higher austenitizing temperatures. This could be explained by the non-equilibrium segregation mechanism of boron atoms. When the Nb-added boron steel specimens were austenitized at higher temperatures, it is possible that Nb and carbon atoms present in the austenite phase retarded the diffusion of carbon towards the austenite grain boundaries during cooling due to the formation of NbC precipitate and Nb-C clusters, thus preventing the precipitation of $M_{23}(C,B)_6$ along the austenite grain boundaries and thereby improving the hardenability of the boron steels. As a result, because it considerably decreases the transformation finish temperature and prohibits the nucleation of proeutectoid ferrite even at the slow cooling rate of $3^{\circ}C/s$, irrespective of the austenitizing temperature, the addition of 0.05 wt.% Nb had nearly the same hardenability-enhancing effect as did the addition of 0.2 wt.% Mo.