• 한국주조공학회지
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• 제8권3호
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• pp.310-321
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• 1988

This study is aimed to investigate the effects of the multi-phase(ferrite-bainite-martensite) on the strengthening and toughening in ductile cast iron. All the specimen were austenitized at eutectoid transformation temperature range(${\alpha}+{\gamma}$) for 1hr and austempered at $300^{\circ}C$ and $400^{\circ}C$ for various holding time, and then quenched in iced water for multi - phase (${\alpha}-B-M$). When the volume fraction of martensite is below 15%, excellent maximum fracture load can be obtained due to strengthening by the fine martensite, but, with increasing of volume fraction over 15%, it was decreased drastically. The martensite size became finer and the shape of it changed from bar to spherical type with increasing of austempering holding time. The higher the austenitizing temperature is, the more preferential is the formation of austenite phase around the graphite nodules improving strength and toughness of austempered ductile cast iron.

• 한국세라믹학회지
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• 제34권2호
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• pp.171-174
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• 1997

산소포논(phonon)이 Yttiria안정화 정방정 지르코니아 소결체(Yttria Stabilized Tetragonal Zirconia Po-lycrystals, Y-TZP)의 저온열화에 큰 영향을 미치는 사실을 실험적으로 밝혔다. Y-TZP의 저온열화 (정방정$\longrightarrow$단사정 상전이) 현상은 Y-TZP의 16O을 18O으로 치환함으로써 급격히 저하되었다. 이는 16O이 보다 무거운 18O으로 치환됨에 따라 임계변위 이상에서 산소원자가 존재할 확률이 감소하는 데 기인하는 것으로 설명하였다.

• 한국전기전자재료학회:학술대회논문집
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• 한국전기전자재료학회 2003년도 춘계학술대회 논문집 초전도 자성체 연구회
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• pp.42-45
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• 2003

The phase transformation of $REBa_2Cu_3O_{7-x}$ (RE=Nd, Gd, Dy) was investigated using isothermal heat-treatment and continuous cooling in air. During continuous cooling, the $REBa_2Cu_3O_{7-x}$ (RE=123) superconducting phase with well-distributed $REBa_2Cu_3O_{7-x}$ (RE-211) was obtainde at a cooling rate of $0.001^{\circ}C$/s. Single phase RE-123 (Nd, Gd, Dy) was stable at $1050^{\circ}C$, $1050^{\circ}C$, and $950^{\circ}C$ during isothermal heat-treatment, respectively. Above these temperatures the RE-211 phase existed within the RE-123 grains. The RE-123, RE-211, $BaCu_2Od_2$, and CuO phases coexisted at $50^{\circ}C$ below the partial melting temperature for each respective rare-earth RE-123.

• 한국윤활학회:학술대회논문집
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• 한국윤활학회 2001년도 제33회 춘계학술대회 개최
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• pp.346-353
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• 2001

Zirconia powder containing 3 mol% yttria(3Y-PSZ) with and with out Fe$_2$O$_3$ addition was coated on tile cast iron substrate by plasma spraying method. The erosion experiments were performed at temperatures from $25^{\circ}C$ to $600^{\circ}C$. A gas blast type erosion tester was used to examine erosion behavior of the specimens. The results of 3Y-PSZ coatings showed that tile erosion rate had maximum value at 40$0^{\circ}C$. It coincided with tile results of phase transformation tetragonal phase to monoclinic phase caused by low temperature thermal degradation. The tensile stress relaxation and the micro-hardness improvement significantly influenced on the erosion rate at $600^{\circ}C$. In the case of Fe$_2$O$_3$ added 3Y-PSZ coatings, the erosion rate of tested at $25^{\circ}C$ showed maximum value at 5.0 mol% Fe$_2$O$_3$ added coating. This tendency is caused by the improvement of mechanical properties and the tensile residual stress. The erosion rate at 200'c and 400'L showed significantly decrease by Fe203 addition. This decrease is believed to be the stabilization of the tetragonal phase and the increase of micro-hardness.

• 한국세라믹학회지
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• 제21권2호
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• pp.149-155
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• 1984

The effect of $ZrO_2$ dispersed phase on the mechanical properties in $Al_2O_3$-$ZrO_2$system has been studied. There are both metastable tetragonal phase and stable monoclinic phase of $ZrO_2$particles diespersed in Al2O3 matrix at room temperature. Metastable tetragonal $ZrO_2$ changes to the stable monoclinic structure within the stress field of the crack. And microcracks are formed by the expansion of $ZrO_2$during the tetragonal-monoclinic transformation on cooling. Therefore stress-induced phase transformation and inclusion-induced microcracking contribute to the mec-hanical properties of $Al_2O_3$-$ZrO_2$system. Sintered composites containing 10m/o $ZrO_2$ yield KiC values of 6.5MN/$m^{3/2}$ much greater than that of pure $Al_2O_3$ This increase results from microcrack extension and stress-induced phase transformation absor-bing energy by crack propagation. Flexural strength of composites is decreased considerably in comparison with pure $Al_2O_3$ This decrease results from microcrack as a crack former and higher porosity than pure $Al_2O_3$.

• 자원리싸이클링
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• 제29권6호
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• pp.73-78
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• 2020

선탄 폐석의 유리 소재 원료로의 활용을 위해 선탄 폐석의 고온 상 전위 거동 및 Na2CO3의 첨가에 따른 유리질(비정질)화 실험을 실시하였다. 실험 결과 700~1,100 ℃에서 소성된 선탄폐석에는 mullite가 생성되고, 1,450 ℃에서는 mullite와 cristobalite만이 존재하였다. 선탄 폐석의 유리질화는 Na2CO3 첨가됨에 따라 진행되었으며, Na2CO3 10 wt.% 첨가 후 1,450 ℃ 온도에서 소성된 선탄 폐석의 유리질화는 97.9 wt.%로 나타났다. 그러나 Na2CO3가 20 wt.% 첨가된 선탄 폐석의 시료의 경우, 1,100 ℃에서의 2차 재소성 과정에서 nepheline(Na2O·Al2O3·2SiO2)이 생성되었으며, 이를 통해 선탄폐석의 유리질화를 위한 최적의 Na2CO3 첨가량은 10 wt.%로 나타났다.

• 열처리공학회지
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• 제15권1호
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• pp.9-15
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• 2002

Deformation behavior of nickel-rich Ti-51.5at.%Ni single crystals was investigated over a wide range of temperatures(77 to 440K) and strain levels(up to 9%) in compression. These alloys combined superior strength with wide range of pseudoelasticity temperature interval(~200K). The slip deformation in [001] orientation did not occur due to the prevailing slip system, and consequently, exhibited pseudoelastic deformation at temperatures ranging from 77 to 283K and 273 to 440K for the solutionized and over-aged cases, respectively. The critical transformation stress levels were in the range of 800 to 1800MPa for the solutionized case, and 200 to 1000MPa for the over-aged case depending on the temperature and specimen orientation. These stress levels are considerably higher compared to these class of alloys having lower Ni contents. The maximum transformation strains, measured from incremental straining experiments in compression, were lower compared to the phenomenological theory with Type II twinning. A compound twinning model depending on the successive austenite(B2) to intermediate phase(R) to martensite(B19') transformation predicts lower transformation strains compared to the Type II twinning case.

• 한국재료학회지
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• 제4권5호
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• pp.524-534
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• 1994

소량의 misch metal과 Zr을 함유한 CuZnAI형상기억 합금의 변태온도에 미치는 열사이클 및 기계적 성질 변화에 대하여 고찰하였다. 합금원소 첨가에 따라 결정립에 매우 미세화 되었으며 용체화 처리후 100~$350^{\circ}C$구간에서 경도값 변화를 조사하기 위하여 post quench aging과 step quench aging처리한 결과 $200^{\circ}C$와 $250^{\circ}C$에서 최고의 경도값을 나타냈다. $M_f$온도이하에서 인당시험한 결과 파단강도와 연실율은 결저립이 미세할수록 증가하는 경향을 보였다. 또한 파단강도는 as quenching처리한 경우보다 post quench aging처리한 경우에 보다더 증가하였다. $\beta$-상에서의 시효는 $M_s$온도를 강하시켰으며 마르텐사이트상에서의 시효는 $A_s$ 온도를 증가시켰다. post quench aging 에 따른 $A_s$의 변화는 $\beta$에서의 회복율에 기여하였으며 변태온도 ($A_s-M_s$)히스테리시스는 열사이클에 의하여 증가하는 경향을 보였다.

• 제어로봇시스템학회:학술대회논문집
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• 제어로봇시스템학회 2000년도 제15차 학술회의논문집
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• pp.554-554
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• 2000

To improve mechanical properties of Cu-Al-Ni alloy by the grain refinement, Cu-Al-Ni SMA ribbons were fabricated by melt spinning apparatus. The variations of microstructure, mechanical properties and transformation characteristics with the condition of rapid solidification and annealing time-temperature were investigated in Cu-Al-Ni SMA ribbons. The ribbons fabricated by melt spinning obtained around 1.5nm in width and 50-60${\mu}{\textrm}{m}$ in thickness. With increasing wheel speed in order of 10m/s, 15m/s, 20m/s, 30m/s and 3m/s, the grain size was decreased in order of 10${\mu}{\textrm}{m}$, 6.25${\mu}{\textrm}{m}$, 5.5${\mu}{\textrm}{m}$, 3${\mu}{\textrm}{m}$ and 3${\mu}{\textrm}{m}$. $M_{s}$ and $A_{s}$ temperature were decreased with decreasing grain size. By X-ray diffraction test, ordered $\beta$$_1$ phase was observed in all the SMA ribbons and the volume friction of it was increased with increasing wheel speed. With increasing wheel speed, strain was increased from 4.2% to 5.8% and fracture mode has changed from mixture of intergranular and dimple fracture to mixture of fiber structure and dimple fracture. The grain size of ribbon heat-treated at $600^{\circ}C$ was increased with increasing time. In the heat-treated ribbons at 55$0^{\circ}C$, ${\gamma}$$_2$ phases were observed.d.d.

• Bulletin of the Korean Chemical Society
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• 제12권5호
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• pp.490-494
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• 1991

The ${\beta} to {\alpha}$ phase transition in silver iodide is studied with the (N, V, E) and (N, P, T) molecular dynamics (MD) method. In experiments, the phase transition temperature is 420 K. Upon heating of ${\beta}$ form, the iodine ions undergo hcp to bcc transformation and silver ions become mobile. MD simulations for the ${\beta}$ and ${\alpha}$ phases are carried out at several temperatures and the radial distribution functions (rdf) are obtained at those temperatures in the (N, V, E) ensemble. But the phase transition is not found in our calculation. Next the phase transition is studied with the (N, P, T) MD and we find some evidences of phase transition. At 3 Kbars and 2 Kbars the phase transition temperatu re is about 300 K. For 3.55 Kbars, the phase transition is higher (420 K) than the low pressure case. The phase transition temperature is somewhat dependent on the pressure in our calculations.