• Journal of the Korean Ceramic Society
• /
• v.33 no.6
• /
• pp.637-644
• /
• 1996

Phase stability and isothermal phase transformation during gaging at 25$0^{\circ}C$ were investigated in yttria stabilized zirconia powders prepared from hydrolysis of zirconium isopropoxide. The stability of tetragonal phase at room temperature in zirconia powder was decreased with calcination temperature but increased with the addition of yttria content. During aging at 25$0^{\circ}C$ in humid atmosphere isothermal phase transformation occurred in tetragonal zirconia powder stabilized by constraint effect not by alloying effect and grain size effect. Many twins and microcrackings were found in transformed monomlinic zirconia particles.

• Structural Engineering and Mechanics
• /
• v.68 no.5
• /
• pp.519-526
• /
• 2018

In this article, experimental training of the commercial available shape memory alloy fibre (SMA) fibre under the combined thermomechanical loading is reported. SMA has the ability to sense a small change in temperature (${\geq}10^{\circ}C$) and activated under the external loading and results in shape change. The thermomechanical characteristics of SMA at different temperature and mechanical loading are obtained through an own lab-scale experimental setup. The analysis is conducted for two types of the medium using the liquid nitrogen (cold cycle) and the hot water (heat cycle). The experimental data indicate that SMA act as a normal wire for Martensite phase and activated behavior i.e., regain the original shape during the Austenite phase only. To improve the confidence of such kind of behavior has been verified by inspecting the composition of the wire. The study reveals interesting conclusion i.e., while SMA deviates from the equiatomic structure or consist of foreign materials (carbon and oxygen) except nickel and titanium may affect the phase transformation temperature which shifted the activation phase temperature. Also, the grain structure distortion of SMA wire has been examined via the scanning electron microscope after the thermomechanical cycle loading and discussed in details.

• Transactions of Materials Processing
• /
• v.17 no.4
• /
• pp.249-256
• /
• 2008

Combined phase transformation and heat transfer was considered on the simulation of hot press forming process, using material properties modeler, $JMatPro^{(R)}$ and a finite element package, $DEFORM^{TM}$-HT. In order to obtain high temperature mechanical properties and flow curves for different phases, a material properties modeler, $JMatPro^{(R)}$ was used, avoiding expensive and extensive high temperature materials tests. The results successfully show that the strength of hot press forming parts may exhibit different strength in the same parts, depending on the contact of blank with tooling. It was also shown effectively that the strength of the parts can be controlled by designing appropriate cooling paths and coolants. This was shown in terms of different heat convection coefficient in the calculation. Overall, current combination of software was shown to be an effective tool for the tool and process design of hot forming process, although the material modeler needs to be additionally verified by an appropriate set of high temperature materials test.

• Proceedings of the Korean Institute of Electrical and Electronic Material Engineers Conference
• /
• 2003.11a
• /
• pp.59-62
• /
• 2003

This study investigated the phase transformation of the $REBa_2Cu_3O_{7-x}$ (RE=Nd, Gd, By) superconductor, and CCT (Continuous-Cooling-Transformation) along with the TTT (Time-Temperature-Transformation) diagrams are suggested according to the isothermal and continuous cooling heat-treatments. According to result of fabricated single crystal of RE-123 superconductor through TSMG method based on phase transformation neted among heat treatment process, when the ionic radius elements was decreased, RE-211 phase was well-distributed. According to result that examine about seed of pretreatment effect of TSMG method, magnetic hysteresis improved when preprocess among oxygen atmosphere in same seed. and used after. Effect of miscut expressed good superconducting special quality in case miscut uses big seed.

• Proceedings of the Korean Powder Metallurgy Institute Conference
• /
• 2006.09b
• /
• pp.1232-1233
• /
• 2006

To co-fire with commercial LTCC (Low Temperature Co-fired Ceramic) materials at $850^{\circ}C{\sim}880^{\circ}C$, different contents of $B_2O_3$ were added to the $Bi_2O_3-ZnO-Nb_2O_5$ (BZN) ceramics. According to the test results, the cubic phase of BZN was transformed into orthorhombic in all the test materials. $BiNbO_4$ phase was formed in test materials with $2{\sim}5wt%$ of $B_2O_3$ addition. The phase transformation of cubic BZN was controlled during the synthesis process with excess ZnO content. The Cubic and orthorhombic phases of BZN could coexist and be sintered densely at $850^{\circ}C/2hr$.

• Proceedings of the Korean Vacuum Society Conference
• /
• 1999.07a
• /
• pp.163-163
• /
• 1999

MOSFET, MESFET 그리고 MODFET는 Logic ULSIs, high speed ICs, RF MMICs 등에서 중요한 역할을 하고 있으며, 그것의 gate electrode, contact, interconnect 등의 물질로는 refractory metal을 이용한 CoSi2, MoSi2, TaSi2, PtSi2, TiSi2 등의 효과를 얻어내고 있다. 그중 TiSi2는 비저항이 가장 낮고, 열적 안정도가 좋으며 SAG process가 가능하므로 simpler alignment process, higher transconductance, lower source resistance 등의 장점을 동시에 만족시키고 있다. 최근 소자차원이 scale down 됨에 따라 TiSi2의 silicidation 과정에서 C49 TiSi2 phase(high resistivity, thermally unstable phase, larger grain size, base centered orthorhombic structure)의 출현과 그것을 제거하기 위한 노력이 큰 issue로 떠오르고 있다. 여러 연구 결과에 따르면 PAI(Pre-amorphization zimplantation), HTS(High Temperature Sputtering) process, Mo(Molybedenum) implasntation 등이 C49를 bypass시키고 C54 TiSi2 phase(lowest resistivity, thermally stable phase, smaller grain size, face centered orthorhombic structure)로의 transformation temperature를 줄일 수 있는 가장 효과적인 방법으로 제안되고 있지만, 아직 그 문제가 완전히 해결되지 않은 상태이며 C54 nucleation에 대한 physical mechanism을 밝히진 못하고 있다. 본 연구에서는 증착 시 기판온도의 변화(400~75$0^{\circ}C$)에 따라 silicon 위에 DC/RF magnetron sputtering 방식으로 Ti/Si film을 각각 제작하였다. 제작된 시료는 N2 분위기에서 30~120초 동안 500~85$0^{\circ}C$의 온도변화에 따라 RTA법으로 각각 one step annealing 하였다. 또한 Al을 cosputtering함으로써 Al impurity의 존재에 따른 영향을 동시에 고려해 보았다. 제작된 시료의 분석을 위해 phase transformation을 XRD로, microstructure를 TEM으로, surface topography는 SEM으로, surface microroughness는 AFM으로 측정하였으며 sheet resistance는 4-point probe로 측정하였다. 분석된 결과를 보면, 고온에서 제작된 박막에서의 C54 phase transformation temperature가 감소하는 것이 관측되었으며, Al impuritydmlwhswork 낮은온도에서의 C54 TiSi2 형성을 돕는다는 것을 알 수 있었다. 본 연구에서는 결론적으로, 고온에서 증착된 박막으로부터 열적으로 안정된 phase의 낮은 resistivity를 갖는 C54 TiSi2 형성을 보다 낮은 온도에서 one-step RTA를 통해 얻을 수 있다는 결과와 Al impurity가 존재함으로써 얻어지는 thermal budget의 효과, 그리고 그로부터 기대할 수 있는 여러 장점들을 보고하고자 한다.

• Applied Microscopy
• /
• v.43 no.1
• /
• pp.40-45
• /
• 2013

Phase transformation by the Mn-deprivation was observed in the high-Mn twinning-induced plasticity-aided steel. Mn-depletion was induced by the formation of Mn-O oxide during the dew-point control process at temperature above $-20^{\circ}C$, which changed austenitic parent phase to multi-grained ferrite. Mixture of Al-O, Al-Mn-Si-O oxides were observed at the grain boundaries of transformed ferrite.

• Proceedings of the Korean Society for Technology of Plasticity Conference
• /
• 2003.05a
• /
• pp.172-175
• /
• 2003

Run-Out-Table is the region between EDT and CT. Hot killed strip is cooled by air and water in ROT. In this procedure, phase transformation and shape deformation occur due to temperature drop. Because of un-ideal cooling condition, deformation of strip and non-uniform phase distribution come into existence. This phenomenon affects the strip property and lead th the existence of residual stress. And it exerts effects on the Coiling process, Coil Cooling process, and Un-coiling process. Through these process, the residual stresses of strip are more larger and unbalance of these stresses become more severe. Finite element (FE) based models for the analysises of non-steady state heat transfer and elastoplastic deformation are described in this investigation. The analysises of thermodynamics and phase transformation kinetics are suggested also. Using the ROT simulation result coiling process and coil cooling process simulations are carried out.

• Journal of the Korean Ceramic Society
• /
• v.42 no.5 s.276
• /
• pp.326-332
• /
• 2005

Phase transformation effects on mechanical properties of $Ge_2Sb_2Te_5$, which is a promising candidate material for Phase Change Random Access Memory (PRAM), were studied. $Ge_2Sb_2Te_5$ thin films, which was thermally annealed with different conditions, were analyzed using XRD, AFM, 4-point probe method and reflectance measurement. As the temperature and the dwelling time increased, crystallity and grain size increased, which enhanced elastic modulus and hardness. Furthermore, N2 doping, which was used for better electrical properties, was proved to decrease elastic modulus and hardness of $Ge_2Sb_2Te_5$.

• Journal of Biomedical Engineering Research
• /
• v.17 no.2
• /
• pp.247-254
• /
• 1996

The relationship between the isothermal age-hardening behavior and the phase transformation in the commercial dental Au-Ag-Cu-Pd alloy was investigated Age-hardening was mostly attributed to the lattice distortions of the supersaturated w phase resulting from the transformation to the metastable phasel which were more distinct at lower aging temperature. The lattice distortions resulting from the transformation of the metastable phases to the equilibrium phases also made a contribution to the age-hardening.