• Proceedings of the Korean Society For Composite Materials Conference
• /
• 2000.04a
• /
• pp.139-142
• /
• 2000

The SiCp/AC8A composites were fabricated by the pressureless metal infiltration process successfully. The effect of additional Mg, which were mixed with SiC particles to promote interfacial wetting between the reinforcement and matrix alloy, and particle size on the mechanical properties was investigated. By increasing the additional Mg content the hardness of SiCp/AC8A composites was increased due to the hard reaction products, but the bending strength was decreased by the excess reaction of Mg and high porosity level when the additional Mg content is over 7%. The Hardness and bending strength was increased by decreasing the size of SiC particle.

• Journal of the Korean Ceramic Society
• /
• v.28 no.8
• /
• pp.654-660
• /
• 1991

Stabilized Zirconia (3 mol % Yttria, 3Y-TZP) was joined with intermetallic compound NiTi which has similar thermal expansion coefficient. The optimum bonding condition was determined by the Taguchi Method. Under the optimum bonding condition, the 4-point bending strength was as high as 400 MPa. bonding interfaces were examined by optical microscope, SEM, and TEM; reaction products were identified by XRD and TEM, The relationship between products and strength was examined.

• Transactions on Electrical and Electronic Materials
• /
• v.14 no.2
• /
• pp.53-58
• /
• 2013

Graphene-based polymer nanocomposites are very promising candidates for new high-performance materials that offer improved mechanical, barrier, thermal and electrical properties. Herein, an approach is presented to improve the mechanical, thermal and electrical properties of unsaturated polyester resin (UPR) by using graphene nano sheets (GNS). The extent of dispersion of GNS into the polymer matrix was also observed by using the scanning electron microscopy (SEM) which indicated homogeneous dispersion of GNS through the UPR matrix and strong interfacial adhesion between the GNS and UPR matrix were achieved in the UPR composite, which enhanced the mechanical properties. The tensile strength of the nanocomposites improved at a tune of 52% at a GNS concentration of 0.05%. Again the flexural strength also increased around 92% at a GNS concentration of 0.05%. Similarly the thermal properties and the electrical properties for the nanocomposites were also improved as evidenced from the differential scanning caloriemetry (DSC) and dielectric strength measurement.

• Proceedings of the KWS Conference
• /
• 2005.06a
• /
• pp.51-53
• /
• 2005

• Korean Journal of Materials Research
• /
• v.28 no.12
• /
• pp.738-747
• /
• 2018

For the aerospace structural application of high-strength 2xxx series aluminum alloys, stress corrosion cracking(SCC) behavior in aggressive environments needs to be well understood. In this study, the SCC sensitivities of 2024-T62, 2124-T851 and 2050-T84 alloys in a 3.5 % NaCl solution are measured using a constant load testing method without polarization and a slow strain rate test(SSRT) method at a strain rate of 10-6 /sec under a cathodic applied potential. When the specimens are exposed to a 3.5 % NaCl solution under a constant load for 10 days, the decrease in tensile ductility is negligible for 2124-T851 and 2050-T84 specimens, proving that T8 heat treatment is beneficial in improving the SCC resistance of 2xxx series aluminum alloys. The specimens are also susceptible to SCC in a hydrogen-generating environment at a slow strain rate of $10^{-6}/sec$ in a 3.5 % NaCl solution under a cathodic applied potential. Regardless of the test method, low impurity 2124-T851 and high Cu/Mg ratio 2050-T84 alloys are found to have relatively lower SCC sensitivity than 2024-T62. The SCC behavior of 2xxx series aluminum alloys in the 3.5 % NaCl solution is discussed based on fractographic and micrographic observations.

• Korean Journal of Metals and Materials
• /
• v.48 no.2
• /
• pp.122-132
• /
• 2010

Higher strength and fracture toughness of reactor pressure vessel steels can be obtained by changing the material specification from that of Mn-Mo-Ni low alloy steel (SA508 Gr.3) to Ni-Mo-Cr low alloy steel (SA508 Gr.4N). However, the operation temperature of the reactor pressure vessel is more than $300^{\circ}C$ and the reactor operates for over 40 years. Therefore, we need to have phase stability in the high temperature range in order to apply the SA508 Gr.4N low alloy steel for a reactor pressure vessel. It is very important to evaluate the temper embrittlement phenomena of SA508 Gr.4N for an RPV application. In this study, we have performed a Charpy impact test and tensile test of SA508 Gr.4N low alloy steel with changing impurity element contents such as Mn and P. And also, the mechanical properties of these low alloy steels after longterm heat treatment ($450^{\circ}C$, 2000hr) are evaluated. Further, evaluation of the temper embrittlement by fracture analysis was carried out. Temper embrittlement occurs in KL4-Ref and KL4-P, which show a decrease of the elongation and a shifting of the transition curve toward high temperature. The reason for the temper embrittlement is the grain boundary segregation of the impurity element P and the alloying element Ni. However, KL4-Ref shows temper embrittlement phenomena despite the same contents of P and Ni compared with SC-KL4. This result may be caused by the Mn contents. In addition, the behavior of embrittlement is not largely affected by the formation of $M_3P$ phosphide or the coarsening of Cr carbides.

• Corrosion Science and Technology
• /
• v.21 no.2
• /
• pp.130-137
• /
• 2022

In this work, the degradation of high-pressure superheater tubes exposed to the flame of a duct burner in a heat recovery steam generator of a district heating system was evaluated. To assess the deterioration of the used superheater tube, the microstructure, microhardness, and tensile properties were investigated by comparison to an unused tube. The study found that a fin bound at the outer surface of the used tube became fragile only in the location facing the flame. This indicates that the tube was directly exposed to the flame from the duct burner or underwent abnormal overheating. While the unused tube showed a uniform value in hardness and equiaxial grain structure, the used tube revealed a decrease in hardness up to 105 HV and an increase in grain size with a plate-like morphology in the location facing the flame. The coarsening of the grain structure by the flame weakened the mechanical properties of yield strength, tensile strength, and elongation.

• Proceedings of the Korean Society For Composite Materials Conference
• /
• 2002.05a
• /
• pp.207-210
• /
• 2002

Metal matrix composites(MMCs) are increasingly attractive for high technology components such as aerospace applications and transportations due to their high strength, stiffness, and toughness. Many processes for fabricating MMCs have been developed, and relatively simple Foil-Fiber-Foil method is usually employed in solid state consolidation processes. During the consolidation processes at high temperature, densification occurs by the inelastic flow of the matrix materials, and the process is coupled with the conditions of pressure, temperature and volume fraction of fiber and matrix materials. This is particularly important in titanium matrix composites, and thus a generic model based on micro-mechanical approaches enabling the evolution of density over time to be predicted has been developed. The mode developed is then implemented into FEM so that practical process simulation has been carried out. Further the experimental investigation of the consolidation behavior of SiC/Ti-6Al-4V composites using vacuum hot pressing has been performed, and the results obtained are compared with the model predictions.

• The Korean Journal of Ceramics
• /
• v.4 no.3
• /
• pp.227-230
• /
• 1998

Alumina($Al_2O_3$)-Titanium Diboride($TiB_2) particulate composites were fabricated by hot pressing of the powder mixture that was prepared from Self-propagating High Temperature Synthesis (SHS) product and commercial powders. Their propeties were examined in order to find feasibility of using SHS for making the high performance ceramic composite. $TiB_2 particles obtained by grinding the SHS product were finer than the commercial powders. Hot pressed sample containing the SHS products exhibited higher strength than the one prepared from the commercial powders.

• Proceedings of the Korean Powder Metallurgy Institute Conference
• /
• 2006.09a
• /
• pp.327-328
• /
• 2006

We have demonstrated that textured $Al_2O_3-mullite-SiC$ nanocomposites can be fabricated by slip casting followed by partial oxidation - reaction sintering of mixed suspensions of $Al_2O_3$ and SiC powders in a high magnetic field. The sintered density was changed by the degree of oxidation at 1200C and 1300C. The degree of orientation of alumina in the nanocomposite was examined on the basis of the X-ray diffraction patterns and scanning electron micrographs. It is confirmed that alumina-oriented nanocomposites were fabricated. The three-point bending strength at room temperature was observed for the nanocomposites.