• Proceedings of the Korea Association of Crystal Growth Conference
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• 1997.06a
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• pp.19-22
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• 1997

The surface modificaion of alumina by $Al_2$O$_3$/SiC nanocomposite coating was studied in terms of processing and microstructure. A powder slurry of 5 vol% SiC composition was dipcoated onto presintered alumina bodies and pressurelessly sintered at 1$700^{\circ}C$ for 2 h in $N_2$. The used of organic binder and plasticizer in the slurry preparation, and the control of the density of presintered alumina body were found to be necessary to avoid cracking and warping during processing. The nanocomposite coating well bonded to the alumina body with thickness about 110 ${\mu}{\textrm}{m}$. The average grain size of coating (2 ${\mu}{\textrm}{m}$) was much finer than that of alumina body (13 ${\mu}{\textrm}{m}$). Fracture surface observations revealed mostly transgranular fracture for the coating, whereas intergranular fracture for the alumina body. Some pores (about 6%) were observed in the coating layer, although the alumina body showed fully dense microstructure.

• Transactions of the Korean Society of Mechanical Engineers
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• v.5 no.2
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• pp.110-121
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• 1981

In order to study on the fracture behavior and the fracture thoughness of combined structure, the specimens, structural steel (SM28C) and 6:4 brass are annealed for ductility and investigated for the befavior of fracture and the absorbed energy at the variation of the impact velocity. The results obtained by this study are as follows: (1)The maximum load increases with the impact velocity, but in the condition of constant impact velocity it decreases as the ductility increases. (2)The absorbed energy increases with the impact velocity, but in the condition of constant impact velocity it is constant as the ductility increases. (3)In the case of the combined structure of peralite and ferrite, the microcracks initiates and propagates mainly in the ferrite structure intergranular in accompany with the slip, and the slip concentration phenomena occur in the boundary of pearlite structure However, in case of the combined structure of .alpha. and ..betha. phase, the microcracks initiates and propagares mainly in the .alpha. phase intergranularly, and slip concentration phenomena not ocur in the boundary of .betha. phase.

• Journal of the Korean Society of Safety
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• v.12 no.1
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• pp.19-28
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• 1997

This study was made of the effect of cold working on the stress corrosion cracking(SCC) of austenitlc 304 stainless steel in boiling 42% $MgCl_2$ solution. For this experiment, specimens cold-worked of 0%, 10%, 20%, 30%, 40% were fabricated respectively, and then experiments of mechanical properties and stress corrosion cracking(SCC) of these specimens were carried out. The results of these experiments indicate that the maximum resistance to SCC showed at 20% of cold working degree and that the SCC susceptibility depended on the volume fraction of deformation-induced martensite by cold working and the work hardening of matrix. On the other hand, the fracture mode was changed. This phenomenon was considered that deformation-induced martensite was grown from transgranular fracture mode to intergranular fracture mode and caused by increased of dislocation density along the slip planes.

• Journal of Powder Materials
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• v.6 no.2
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• pp.152-162
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• 1999

The present study is concerned with the effect of PM process variables on the microstructure by using atomized superalloy powders. It is suggested that the inhomogeneity of composition is strongly dependent on the process variables. The contents of segregation elements of plasma rotating electrode process (PREP) powders are larger than those of Ar atomization (AA) powders. As HIP treatment temperature in-increases, the secondary phases on the prior particle boundaries (PPB) have continuous,uniform distribution and high density, but the amount of PPB decreases suddenly at 1150$^{\circ}$C. Segregated phases on the PPB are identified to be MC type carbide. Brittle MC type carbides on the PPB provide fracture initiation sites and preferred fracture path, thereby leading to intergranular type brittle fracture.

• 연구논문집
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• s.30
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• pp.121-128
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• 2000

The failed tube received for this study has been used for approximately 10 year at $330^{\circ}C$ in a steam production boiler tube was fractured in the transversed direction to tube length, and fracture mode was typically intergranulas type without the plastic deformation. The fracture surface was covered by the oxide scale formed from the intermal high pressure steam at high temperature. The microstructure was not nearly thermal-degraded during the service. From this result, we can conclude that the oxide film was proferentialy formed into the grainboundary and this grainboundary oxide film was brittle-fractured by the thermal stress in the longitudinal direction to the tube brittle intergranular fracture mode.

• Proceedings of the Korean Powder Metallurgy Institute Conference
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• 2006.09b
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• pp.1082-1083
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• 2006

Carbon nanotube (CNT) reinforced hydroxyapatite (HAp) composites were fabricated by using the spark plasma sintering process with surfactant modified CNT and HAp nano powder. Without the dependency on sintering temperature, the main crystal phase existed with the HAp phase although a few contents of ${\beta}-TCP$ (Tri calcium phosphate) phase were detected. The maximum fracture toughness, $(1.27\;MPa.m^{1/2})$ was obtained in the sample sintered at $1100^{\circ}C$ and on the fracture surface a typical intergranular fracture mode, as well as the pull-out pmhenomenon of CNT, was observed.

• Journal of the Korean Ceramic Society
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• v.29 no.10
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• pp.797-805
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• 1992

Al2O3-20 wt% ZrO2 composite powders to be used as the starting materials of the Al2O3/ZrO2-Spinel composite system were prepared by the use of the emulsion-hot kerosene drying method. The crystalline phase of ZrO2 in the synthesized Al2O3-ZrO2 composite powders was 100% tetragonal but the small amount of t-ZrO2 was transformed into m-ZrO2 after crushing. The hardness, fracture toughness, and flexural strength of the composite, which was sintered at 1650$^{\circ}C$ for 4 hrs after calcining at 1100$^{\circ}C$ for 2 hrs and had the relative density of 99%, were 15.7 GPa, 4.97 MN/m3/2, and 390 MPa, respectively. The fracture form in the sintered composites was found to be the intergranular fracture.

• Journal of the Korean Ceramic Society
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• v.36 no.4
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• pp.372-379
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• 1999

Hihg-toughened ceria-stabilized tetragonal zirconia ceramics with irregular grain shape and undulated grain boundary was prepared by ceria doping. Irregularity of grain shapes was increased with the amount of doped ceria. But in case of the large amount of doped ceria grain boundary was migrated to the reverse direction of DIGM. Ceria-stabilized zirconia ceramics annealed at 1650$^{\circ}C$ for 2h after twice dippings into cerium nitrate solu-tion of 0.2M and sintering at 1500$^{\circ}C$ for 2h showed the highest grain boundary length with a value of 23.6$\mu\textrm{m}$ Ceria concentration difference between convex and concave sides in irregular grains was observed over 1 mol% but not observed in normal grains, Specimens with normal grain shape showed intergranular fracture mode whereas the specimens with irregular grain shape showed transgranular fracture mode.

• Journal of the Korean Society of Safety
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• v.14 no.1
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• pp.41-48
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• 1999

The fatigue life tests were performed in strain control with triangular and hole-time wave-forms at $650^{\circ}C$. The fatigue lifes were investigated according to waveform examining damage mechanisms, which could be used to predict the fatigue life and estimate the remaining life. The results obtained are as follows; The fatigue lifes were in order of the fast-fast>the fast-slow>the slow-fast in the triangular waveforms, and the fatigue lifes in slow-fast waveforms got shorter in the hold-time waveforms. The damage mechanisms of the fracture surfaces were transgranular fracture in the fast-fast, the fast-slow waveforms and intergranular fracture in the slow-fast waveform.

• Proceedings of the KSME Conference
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• 2004.04a
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• pp.78-83
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• 2004

Environmental fatigue crack propagation of CF8M and CF8A steels used in the domestic PWR were investigated on the simulated PWR condition(Temperature: $316^{\circ}C$, Pressure: 15MPa). The test equipment for environmental fatigue(high temperature-high pressure loop, autoclave, load frame, measurement system) were designed. As-received and 60-year aged specimens were used in the test. To compare with environmental fatigue test, another test was performed in the air condition. The fracture surface of specimens were difficult to verify the fracture modes such as striation, intergranular crack and cleavage and so on. As the ferrite content of CF8M is increased, more particles covered fracture surface were peeled.