• Korean Journal of Materials Research
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• v.33 no.10
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• pp.406-413
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• 2023

This study used optical and scanning electron microscopy to analyze the surface oxidation phenomenon that accompanies a γ'-precipitate free zone in a directional solidified CM247LC high temperature creep specimen. Surface oxidation occurs on nickel-based superalloy gas turbine blades due to high temperature during use. Among the superalloy components, Al and Cr are greatly affected by diffusion and movement, and Al is a major component of the surface oxidation products. This out-diffusion of Al was accompanied by γ' (Ni₃Al) deficiency in the matrix, and formed a γ'-precipitate free zone at the boundary of the surface oxide layer. Among the components of CM247LC, Cr and Al related to surface oxidation consist of 8 % and 5.6 %, respectively. When Al, the main component of the γ' precipitation phase, diffused out to the surface, a high content of Cr was observed in these PFZs. This is because the PFZ is made of a high Cr γ phase. Surface oxidation of DS CM247LC was observed in high temperature creep specimens, and γ'-rafting occurred due to stress applied to the creep specimens. However, the stress states applied to the grip and gauge length of the creep specimen were different, and accordingly, different γ'-rafting patterns were observed. Such surface oxidation and PFZ and γ'-rafting are shown to affect CM247LC creep lifetime. Mapping the microstructure and composition of major components such as Al and Cr and their role in surface oxidation, revealed in this study, will be utilized in the development of alloys to improve creep life.

• Proceedings of the Korean Society for Technology of Plasticity Conference
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• 1997.10a
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• pp.228-231
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• 1997

A series of load relaxation tests was performed to determine stress-strain rate curves at high temperatures. Constitutive parameters of GBS and GMD were evaluated from the curves using the recently proposed inelastic deformation theory. Tensile tests and Microsturcture investigations showed deformation behavior as the relaxation test results predicted.

• Korean Journal of Materials Research
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• v.33 no.2
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• pp.77-86
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• 2023

High-temperature oxidation of a Ni-based superalloy was analyzed with samples taken from gas turbine blades, where the samples were heat-treated and thermally exposed. The effect of Cr/Ti/Al elements in the alloy on high temperature oxidation was investigated using an optical microscope, SEM/EDS, and TEM. A high-Cr/high-Ti oxide layer was formed on the blade surface under the heat-treated state considered to be the initial stage of high-temperature oxidation. In addition, a PFZ (γ' precipitate free zone) accompanied by Cr carbide of Cr₂₃C₆ and high Cr-Co phase as a kind of TCP precipitation was formed under the surface layer. Pits of several ㎛ depth containing high-Al content oxide was observed at the boundary between the oxide layer and PFZ. However, high temperature oxidation formed on the thermally exposed blade surface consisted of the following steps: ① Ti-oxide formation in the center of the oxide layer, ② Cr-oxide formation surrounding the inner oxide layer, and ③ Al-oxide formation in the pits directly under the Cr oxide layer. It is estimated that the Cr content of Ni-based superalloys improves the oxidation resistance of the alloy by forming dense oxide layer, but produced the σ or µ phase of TCP precipitation with the high-Cr component resulting in material brittleness.

• Korean Journal of Veterinary Research
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• v.5 no.1
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• pp.1-16
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• 1965

I. A Comparison of Sodium Sulfate Precipitation and Zone(Paper, Agar) Electrophoresis; Many kinds of techniques have been used for fractionating serum proteins. In the present study, using bovine serum, the fractions obtained with sodium sulfate were compared with those determined by zone electrophoresis. 1. Fibrinogen was precipitated with 4 to 10 percent of sodium sulfate. 2. ${\gamma}$-globulin required 10 to 16 percent of the salt for precipitation. 3. ${\beta}$-globulin began to precipitate at 12 percent sodium sulfate, and completed precipitation at approximately 26 percent in paper electrophoresis, while at 22 percent in agar electrophoresis. 4. ${\alpha}$-globulin completed precipitation at 13 to 28 percent sodium sulfate in paper electrophoresis and at 22 percent in agar electrophoresis. 5. Albumin began to precipitate at 14 percent of the salt, and was free from the mixture of globulins approximately at 28 percent in paper electrophoresis, while at 22 percent in agar electrophoresis. The results of comparing fractions by the two methods were as follows: 1. Euglobulin (15%) was equal to the sum of the most ${\gamma}$-globulin and a small quantity of the ${\alpha}$-, and ${\beta}$-globulins. 2. Pseudoglobulin I (15-17.5%) corresponded to the most ${\alpha}$-, ${\beta}$-globulins and a small quantity of albumin. 3. Pseudoglobulin II(18-22%) was a mixture of the ${\alpha}$-, ${\beta}$-globulins and albumin fraction. 4. Albumin (above 22%) contained the most albumin fraction separated by zone electrophoresis and a small quantity of the ${\alpha}$-, and ${\beta}$-globulins. As mentioned above the fractions obtained with sodium sulfate were a mixture of the various proportion of the fractions determined by zone electrophoresis. The solubility of serum fractions to sodium sulfate coincided with the mobility of those by zone electrophoresis. (By percent of sodium sulfate we mean gram of sodium sulfate contained in $100m{\ell}$ of solution). II. Immunological Studies on Serum Protein Fractions with Sodium Sulfate; In the previous report the fractions of bovine serum protein with sodium sulfate compared with those obtained by zone electrophoresis, and the findings were that the former contained various proportion components of the latter. In this study the author studied whether or not the fractions with sodium sulfate are simple component antigenically by immunoelectrophoresis and micro double diffusion test (Immuno-precipitation), using rabbit antiserum to bovine serum. In immunoelectrophoresis, normal bovine serum developed with rabbit antibovine serum showed about ten distinct precipitin arcs. The distribution of these arcs was as follows: 1 albumin, 2 ${\alpha}_1$-, 3 ${\alpha}_2$-, 2 ${\beta}_1$-, ${\beta}_2$-, and 1 ${\gamma}$-globulin (Fig. 7, 9). In micro double diffusion test, five to six precipitation bands could be seen between antigens and antibody, the order of the precipitation bands location is albumin, ${\alpha}$-, ${\beta}$-, and ${\gamma}$-globulin from the side of antiserum well (Fig.19). Frequently the ${\alpha}$-, and ${\beta}$-precipitation bands were separated into two or three precipitation bands, which indicated that these globuline are not a pure component antigenically as shown in immuno-electrophoresis. In both Immunological methods, the two ${\alpha}$-, ${\beta}$-precipitin arcs and bands appeared clear and strong, indicating that the two globulins reacted as strong antigens. The precipitate reaction of ${\gamma}$-globulin was shown at 12 to 16 percent sodium sulfate; ${\beta}$-globulin at 12 to 20 percent; ${\alpha}$-globulin at 12 to 22 percent (immuno-electrophoresis), at 12 to 26 percent (Diffusion); and albumin at above 22 percent. Antigenically euglobulin contained ${\gamma}$-, ${\beta}$-, and ${\alpha}$-globulins, Pseudoglobulin I and Pseudoglobulin II were composed of ${\alpha}$-, and ${\beta}$-globulins, and albumin was a mixture of ${\alpha}$-globulin and albumin determined by zone electrophoresis. The results indicated that the fractions of serum protein obtained by either method were constituents of various proteins antigenically except ${\gamma}$-globulin and albumin by Zone electrophoresis.

• Korean Journal of Materials Research
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• v.32 no.4
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• pp.200-209
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• 2022

In this study, defects generated in the YSZ coating layer of the IN738LC turbine blade are investigated using an optical microscope and SEM/EDS. The blade YSZ coating layer is composed of a Y-Zr component top coat layer and a Co component bond coat layer. A large amount of Cr/Ni component that diffused from the base is also measured in the bond coat. The blade hot corrosion is concentrated on the surface of the concave part, accompanied by separation of the coating layer due to the concentration of combustion gas collisions here. In the top coating layer of the blade, cracks occur in the vertical and horizontal directions, along with pits in the top coating layer. Combustion gas components such as Na and S are contained inside the pits and cracks, so it is considered that the pits/cracks are caused by the corrosion of the combustion gases. Also, a thermally grown oxide (TGO) layer of several ㎛ thick composed of Al oxide is observed between the top coat and the bond coat, and a similar inner TGO with a thickness of several ㎛ is also observed between the bond coat and the matrix. A PFZ (precipitate free zone) deficient in γ' (Ni₃Al) forms as a band around the TGO, in which the Al component is integrated. Although TGO can resist high temperature corrosion of the top coat, it should also be considered that if its shape is irregular and contains pore defects, it may degrade the blade high temperature creep properties. Compositional and microstructural analysis results for high-temperature corrosion and TGO defects in the blade coating layer used at high temperatures are expected to be applied to sound YSZ coating and blade design technology.