• 동력기계공학회지
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• 제11권1호
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• pp.121-126
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• 2007

This study aims at investigating the effect of heat treatment conditions on the dry sliding wear behavior of thermally sprayed Ni-based self-flux alloy coatings. Ni-based self-flux alloy powders were sprayed onto a carbon steel substrate and then heat-treated at 700, 800, 900 and $1000^{\circ}C$ for 30 minutes in a vacuum furnace. Dry sliding wear tests were performed using sliding speed of 0.4 m/s and applied load of 6 N. AISI 52100 ball(diameter 8 mm) was used as counterparts. Microstructure and wear behavior of both as-sprayed and heat-treated Ni-based self-flux alloy coatings were studied using a scanning electron microscope(SEM), energy dispersive X-ray spectroscopy(EDX), electron probe micro-analysis(EPMA) and X-ray diffraction(XRD). It was revealed that microstructure and wear behavior of thermally sprayed Ni-based self-flux alloy coatings were much influenced by heat treatment conditions.

• 대한의용생체공학회:의공학회지
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• 제19권4호
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• pp.333-339
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• 1998

본 연구에서는 혈관폐색을 위한 색전코일의 열처리 제조공정 조건을 연구하였다. 2.92mm의 알루미나 심재에 1차코일을 감은 후 475$^{\circ}C$와 600$^{\circ}C$에서 열처리하여 2차코일을 제조하였으며, 열처리 시간에 따른 2차코일의 피치간격, 내경 및 형상복원성을 평가하였다. 2차코일의 피치간격은 475$^{\circ}C$와 600$^{\circ}C$에서 각각 잠복기를 가진 후 열처리 시간이 증가함에 따라 증가하였다. 2차코일의 내경은 열처리 시간이 증가함에 딸 연속적으로 감소하였다. 이 원인은 열처리 초기에 회복에 의하여 재료의 내부에너지가 감소되면서 2차코일의 피치간격과 내경이 감소되나, 열처리 시간이 증가됨에 따라 텅스텐 표면의 산화물이 형성되면서 탄성이 증가되기 때문에 피치간격이 증가하는 것으로 분석되었다. 2차코일의 형상복원성은 텅스텐코일의 표면에 형성된 텅스텐 산화물이 탄성을 증가시킴으로 인해 열처리 시간이 증가함에 따라 연속적으로 증가하였다. 열처리 온도 영향을 비교하면 산화물형성 속도가 빠른 600$^{\circ}C$가 475$^{\circ}C$보다 더 우수한 형상복원성을 나타내었다. 텅스텐 색전코일의 제조공정 연구결과 2차코일의 피치간격, 내경 및 형상 복원성을 최적화하기 위해서는 600$^{\circ}C$에서 20분간 열처리하는 것이 적절한 조건인 것으로 조사되었다.

• 열처리공학회지
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• 제33권5호
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• pp.226-231
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• 2020

The Cu-Co-Si alloy shows high strength by forming precipitates by aging precipitation heat treatment of supersaturated solid solution treated with solution treatment such as Cu-Ni-Si alloy, and the Co₂Si precipitated phase is dispersed in the copper matrix. The effect of aging treatment on the microstructure, mechanical and electrical properties of Cu-Co-Si alloys for electronic devices was investigated. As a results of SEM/EDS analysis, it was found that Co₂Si precipitates of 30~300 nm size were distributed in grains. By performing the double aging treatment, it was possible to improve the strength and electrical conductivity by dispersing the fine precipitate evenly.

• 열처리공학회지
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• 제11권2호
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• pp.82-91
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• 1998

The elastic modulus and wear resistance in austempered ductile cast iron(ADI) are two important mechanical properties for automobile parts. Therefore, the effect of Cu, Ni, Mo and special austempering treatment such as preheated, prequenched, and step austempering treatments on elastic modulus and wear resistance has been investigated systomatically. As a result, elastic modulus and wear resistance were increased by the addition of Mo-Cu and preheated austempering treatment.

• 대한한방소아과학회지
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• 제14권2호
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• pp.133-140
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• 2000

Purpose : Posterior Neck Pain and Back Pain are common diseases in human daily life. For reducting symptom and treatment of these diseases, many methods have been used and studied until now. The mechanisms of Ceragem Master Heat Bed(R)(Ceragem Co. Seoul, Korea) are infrared-heat therapy from natural nephrite and pressure therapy by up-down movement of natural nephrite ball. Through this study, authors would evaluate the clinical effectiveness of Ceragem Master Heat Bed(CMHB) on relieving posterior neck pain and back pain. Materials and methods : From 12-01-2000 to 01-13-2001, posterior neck pain and back pain patients were selected for experiment group(23patients) and control group(14patients). In both group, Visual Analog Scale(VAS) of pre-treatment stage is above 5 points. Experiment group were cared with acupuncture therapy, buhang therapy and CMHB. Control group were managed with only acupuncture therapy and buhang therapy. They were treated more than three times at least. At pre-treatment and post-treatment stage, we measured VAS for individual patients, and then compared effect of treatment in experiment group and in control group. Statistical analysis was preformed using SAS program. Results : In this study, a mean difference of VAS between pre-treatment and post-treatment stage was large in experiment(CMHB) group more than in control group(p〈0.01). Conclusion : Experiment(CMHB) group was more effective pain relief than control group in the treatment of posterior neck pain and back pain. CMHB was available for stimultaneous application of heat therapy and pressure massage together that gave another effects of mental stability and fatigue recovery. As the results of this study, CMHB could be used as a helpful treatment modality for posterior neck pain and back pain.

• Corrosion Science and Technology
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• 제23권1호
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• pp.64-71
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• 2024

The objective of this study was to investigate corrosion and cavitation-erosion characteristics of the electroless nickel plating layer with heat treatment. The crystallization temperature of the electroless nickel plating layer was about 410 ℃. The phase transformation energy was confirmed to be 12.66 J/g. With increasing heat treatment temperature, the amorphous electroless nickel plating layer gradually changed to crystalline Ni and Ni₃P. At the same time, the crystal grain size was also increased. Additionally, when heat treatment was performed at a temperature above 400 ℃, NiO phase was observed due to oxidation phenomenon. As a result of the electrochemical polarization experiment, the corrosion resistance of the heat-treated electroless nickel plating layers was superior to that of the as-deposited plating layer. This was because crystal grains became larger and grain boundaries decreased during heat treatment. The cavitation-erosion resistance of heat-treated plating layers tended to be superior to that of as-deposited plating layers due to increased microhardness.

• 한국주조공학회지
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• 제10권4호
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• pp.299-308
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• 1990

Ductile cast iron has a good ductility and ductility and toughness than those of gray cast iron, because the shape of graphite is spheroidal. It has been reported that the strengthening and toughening of the ductile cast iron was resulted from the good modification of various matrix structures obtained by the heat treatment or addition of alloying elements. This study aims to investigate the effect of various special heat treatment(Cyclic Heat Treatment, Intermediate Heat Treatment, Step Quenching), austempering and alloying element(Ni) on the strength and toughness of ductile cast iron. The results obtained from this study are summarized as follows. 1) With addition of Ni, the amount of pearlite or bainite were increased and the morphologies of pearlite or bainite became finer by special heat treatments. 2) As the Ni added and not added ductile cast iron were treated by austenitizing at $900^{\circ}C$ and $840^{\circ}C$, in the latter the austenite was mostly formed in the vicinity of eutectic cell boundary, but in the former on the whole matrix. 3) In cyclic heat treatment, the volume fraction of pearlite was increased and the shape of pearlite was fined with increase of the number of cycle. 4) The shape of pearlite was mostly bar type in the intermediate heat treatment, but spheroidal type in step quenching. 5) The mechanical properties of ductile cast iron containing 1.5%Ni austempered at $400^{\circ}C$ for 25min. after austenitizing at $900^{\circ}C$ for 15min. were a good value of hardness 105(HRB), impact energy 12.5(kg.m), tensile strength 112($kg/mm^2$) and elongation 6.8(%).

• 동력기계공학회지
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• 제20권5호
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• pp.29-36
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• 2016

Aluminum alloys have been widely used in engine materials, cold & hot-water storage vessels and piping etc., Furthermore, the aluminum alloy of AC8A have been widely used in mold casting material of engine piston for various vehicles because of its properties of temperature, wear and corrosion resistance. Therefore, it is considered that evaluation of corrosion resistance as well as wear resistance of AC8A material is also important to improve its property and to prolong its lifetime. In previous paper, the effect of solution($510^{\circ}C$:4hrs) and tempering($190^{\circ}C$: 16, 24, and 36 hrs)heat treatments to corrosion resistance and hardness were investigated using electrochemical method. In this study, in order to examine completely the effect of the tempering hours to hardness variation and corrosion resistance, the results of solution($510^{\circ}C$:4hrs) and tempering($190^{\circ}C$: 2, 4, 8 and 12hrs)heat treatments to hardness and corrosion resistance were investigated using electrochemical method. The hardness decreased with solution heat treatment compared to mold casting condition, but its value increased with tempering heat treatment. Furthermore, the corrosion resistance increased with decreasing of the hardness, and decreased with increasing of the hardness reversely. And the tempering heat treatment temperature at $190^{\circ}C$ for 8 hrs exhibited the highest value of the hardness and also indicated the highest corrosion current density. However, the values of hardness and corrosion current density was again increasingly decreased with increasing of tempering hours than 8 hrs, Consequently, it is suggested that decision of the optimum. tempering hours is very important to improve the corrosion or wear resistance.

• 열처리공학회지
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• 제29권3호
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• pp.103-108
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• 2016

In recent years, TRIP steels which are composed of ferrite, bainite, and retained austenite have drawn much attention for automotive sheets due to excellent combination of strength and ductility. The effect of two-step isothermal heat treatment of bainitic transformation on microstructures, especially retained austenites and tensile properties in the conventional TRIP steel was investigated. A two-step isothermal heat treatment, in which 50% bainitic transformation occurred at high temperature, followed by bainitic transformation at low temperature, improves tensile properties, resulting from enhanced mechanical stability of retained austenite against external plastic deformation due to refinement of retained austenites, compared to single-step isothermal heat treatment.

• Progress in Superconductivity
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• 제4권1호
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• pp.90-93
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• 2002

The sintering process of BSCCO 2223 tapes is a complex process that is very sensitive to parameters, such as temperature, oxygen partial pressure, heating and cooling rate and holding time. During the first heat treatment, 2212 phase of precursor powder is partially transformed into 2223 phase and some residual secondary phases, such as $(Bi,Pb)_2$$Sr_2$CuO／sub y／(2201), $(Ca,Sr)_2$CuO／sub y／(2/1AEC), (Ca,Sr)／sub 14／Cu／sub 24／O／sub 41／(14／24 AEC) etc. The secondary phases are difficult to be removed from the BSCCO 2223 matrix on the heat treatment. These secondary phases degrade the critical current density. In order to minimize the amount and size of alkaline earth cuprate(AEC) particles step heat treatment is applied during the first heat treatment under the varying atmosphere. Experimental results showed that by adapting the step heat treatment process, the amount and particle size of the secondary phases in the final tapes are decreased. Consequently, the BSCCO 2223grain texture and Jc properties are improved.