• 열처리공학회지
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• 제18권5호
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• pp.297-304
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• 2005

This study was performed to determine the repair weldability of the damaged Ni type superalloy used for gas turbine blade. The experimental works included the evaluation of the microstructures of the damaged blade, selection of the repair welding procedure, characterization of repair weldment and finding the heat treatment procedures for repaired weldment. The morphology of the microstructure for the base metal was composed of austenite matrix with cubical ${\gamma}^{\prime}$ phase, MC type coarse precipitates located within grain and fine $M_{23}C_6$ type precipitates decorated at grain boundaries. The repair welding process using 90 amp current exhibited the best weld properties showing no weld microcracks. The solution and aging heat treatments of the repaired weldment could recover the original service properties of the damaged blade.

• 연구논문집
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• 통권32호
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• pp.77-84
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• 2002

A martensitic precipitation hardening stainless steel, 17-4PH has been widely used in the aircraft, chemical and nuclear industries for long time, owing to the excellent mechanical properties with corrosion resistance that can be achieved by simple heat treatment. The microstructure and mechanical properties of the 17-4PH stainless steel cast parts for aircraft, such as impeller, are largely affected by heat treatment condition. But the database of heat treatment has not been clearly established in the domestic investment casting industries because the domestic aerospace, industry lags behind the advanced countries. In this study, the microstructural evolution and mechanical properties of cast 17-4PH stainless steel depending on the heat treatment conditions and aging at $400^{\circ}C$ were investigated.

• 열처리공학회지
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• 제11권1호
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• pp.27-34
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• 1998

Effects of different heat treatments on microstructure and damping capacity of Cu-55%Mn alloy were investigated to find an optimum heat treatment condition for a maximum damping capacity. The alloy showed the high level of damping capacity in case of the aging at 375 and $400^{\circ}C$. This is ascribed to the FCC${\rightarrow}$FCT martensitic transformation and microstructural changes from mottled to tweed band type. The damping capacity had a maximum value of 0.33 in logarithmic decrement when the alloy was aged at $375^{\circ}C$ for 14 hours followed by 20 times of thermal cycling between room temperature and $250^{\circ}C$. The refinement of tweed structure by thermal cycling is thought to be responsible for the highest damping capacity.

• 한국생산제조학회지
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• 제8권4호
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• pp.123-129
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• 1999

Although type 316 stainless steel is widely used such as in reactors of petrochemical plants and pipes of steam power plants and s attracting attention as potential basic material for the fast breeder reactor structure alloys in nuclear power plants and is attracting attention as potential basic material for the fast breeder reactor structure alloys in nuclear power plants the effect of precipitates which form during the long term exposure at service temperature on creep properties is not known sufficiently. In this study to investigate the creep properties and the influence of prior aging on the microstructure to form precipitates specimens were first solutionized at 113$0^{\circ}C$ for 20 minutes and then aged for different times of 0 hr, 100 hrs, 1000 hrs and 2200 hrs at 75$0^{\circ}C$ After heat treatments tensile tests both at room temperature and $650^{\circ}C$ and constant load creep ruptuere tests were carried out.

• 한국신뢰성학회지:신뢰성응용연구
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• 제7권4호
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• pp.163-172
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• 2007

Phenomenon, such as hardening, cracking or breaking etc.. of PVC tape for wiring harness by aging were detected on driven automobile in field. Hardening or cracking of PVC tape were confirmed decline of elongation by surrounding stress. The accelerated heat aging test was carried out applying temperature most important factor of aging, and then deduced an equation of useful life using arrhenius model. Prediction method of useful life of PVC tape was developed using miner rule calculating damage value by thermal energy classified temperature by matching deduced equation of useful life and measured temperature value on driven automobile in field.

• International Journal of Automotive Technology
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• 제1권2호
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• pp.71-77
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• 2000

High temperature materials in service are subjected to mechanical damage due to operating load and metallurgical damage due to operating temperature. Therefore, when designing or assessing life of high temperature components, both factors must be considered. In this paper, the effect of tensile hold time on high temperature fatigue crack growth and long term prior thermal aging heat treatment on creep rupture behavior were investigated using STS 316L and STS 316 austenitic stainless steels, which are widely used for high temperature components like in automotive exhaust and piping systems. In high temperature fatigue crack growth tests using STS 316L, as tensile hold time increased, crack growth rate decreased in relatively short tensile hold time region. In long term aged specimens, cavity type microcracks have been observed at the interface of grain boundary and coarsened carbide.

• 한국세라믹학회지
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• 제33권11호
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• pp.1231-1236
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• 1996

The electrode resistance of semiconducting PTC BaTiO3 ceramic material was studied in some detail. Comme-rical In-Ag paste In-Ga alloy and electroless plated Ni as well as evaporated Al were chosen as electrode. The contact resistance of electroded samples were measured by both dc resistivity and ac impedance analysis. The aging effect on contact resistance under cyclic loading from -1$0^{\circ}C$ to 85$^{\circ}C$ was also monitored for the prolonged period of time. In case of Al electroded samples the heat treatment and protective coating had effects on the stability against contact resistance degradation. It was also found that the samples with commercial In-Ag paste and electroless plated Ni electrode had good properties of contact resistance against aging.

• Journal of Mechanical Science and Technology
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• 제18권10호
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• pp.1730-1737
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• 2004

The BI (Ball Indentation) method has the potential to assess the mechanical properties and to replace conventional fracture tests. In this study, the effect of aging on mechanical behavior of 1Cr-1Mo-0.25V steels procured by isothermal aging heat-treatment at four different aging times in the range of 0～1820 hours at 630$^{\circ}C$, were investigated using BI system.

• 한국전기전자재료학회:학술대회논문집
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• 한국전기전자재료학회 2001년도 추계학술대회 논문집 Vol.14 No.1
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• pp.258-261
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• 2001

In this paper, aging characteristics of silicone rubber used for outdoor insulation have been investigated with regards to salt fog condition and heat aging effect. We look over the change of properties of silicone rubber in salt fog chamber with average leakage current monitoring for observing the transformation of surface degradation properties of silicone rubber with different ATH(alumina trihydrate, $Al_2O_3{\cdot}3H_2O$) filler contents. Surface resistivity, SEM(Scanning Electro Microscope) were measured.

• 한국전기전자재료학회:학술대회논문집
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• 한국전기전자재료학회 2001년도 추계학술대회 논문집
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• pp.258-261
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• 2001

In this paper, aging characteristics of silicone rubber used for outdoor insulation have been investigated with regards to salt fog condition and heat aging effect. We look over the change of properties of silicone rubber in salt fog chamber with average leakage current monitoring for observing the transformation of surface degradation properties of silicone rubber with different ATH(alumina trihydrate, Al$_2$O$_3$$.$3H$_2$O) filler contents. Surface resistivity, SEM(Scanning Electro Microscope) were measured.