• Journal of the Korean institute of surface engineering
• /
• v.51 no.1
• /
• pp.62-70
• /
• 2018

Sulfamate plating solution containing a small amount of chloride bath was fabricated to study the properties of the electrodeposited Ni thin films. Effects of the changes of current density and additive concentration on current efficiency, residual stress, surface morphology and microstructure of Ni thin films electrodeposited from Ni sulfamate-chloride baths were investigated. The current efficiency was measured to be more than about 95%, independent of the changes of current density and saccharin concentration in the baths. Residual stress of Ni thin film was appeared to be the compressive stress modes in the range of $5{\sim}30mA/cm^2$ current density. Maximum compressive stress was observed at the current density of $10mA/cm^2$. Compressive stress values of Ni thin/thick films were increased to be about -85~-100 MPa with increasing saccharin concentration from 0 to 0.0195 M(4 g/L). Surface morphology was changed from smooth to nodule surface appearance with increasing the current density. Smooth surface morphology of Ni thin films electrodeposited from the baths containing saccharin was observed, independent of the saccharin concentration. Ni thin/thick films consist of FCC(111), FCC(200), FCC(220), FCC(311) and FCC(222) peaks. It was revealed that the FCC(200) peak of Ni thin films is the preferred orientation in the range of $5{\sim}30mA/cm^2$ current density. The intensity of FCC(200) peak was gradually decreased and the intensity of FCC(111) peak was increased with increasing saccharin concentration in the baths.

• Journal of Aerospace System Engineering
• /
• v.12 no.2
• /
• pp.46-58
• /
• 2018

A two-axis gimbal-type X-band antenna is widely used to transmit bulk image data from high-resolution observation satellites. However, undesirable microvibrations induced by driving the antenna should be attenuated, because they are a main cause of image-quality degradation of the observation satellite. In this study, a pseudoelastic memory alloy (SMA) gear was proposed to attenuate the microvibrations by driving the antenna in an azimuth angle. In addition, the proposed gear can overcome the limitations of the conventional titanium blade gear, which is not still enough and is vulnerable to plastic deformations under excessive torque. To investigate the basic characteristics of the proposed SMA mesh washer gear, a static load test was performed on the thickness of the SMA mesh washer and the rotation of the gear. Moreover, The microvibration measurement test demonstrated that the SMA mesh washer gear proposed in this study is effective for microvibration attenuation.

• Journal of Veterinary Clinics
• /
• v.7 no.2
• /
• pp.511-515
• /
• 1990

Induction of twinning was attempted by transfer of two whole- or demi-embryos in Holstein cows and heifers. Cows were superovulated with follicle stimulating hormone(FSH) administered twice daily in intra-muscular injection. On day of 6.5 to 7 post-estrus, embryos were collected nonsurgically, Normal morulae and early balstocysts were obtained from superovulated cows. The embryos were hisected with a micro-blade made from a razor. Twenty seven pairs of half embryos were successfully produced and 23 pairs of half embryos were transferred to recipients( Group A). Twenty cows were treated with low unit of FSH (3mg${\times}$2,2mg${\times}$2 ; Group B1, 2mg${\times}$2, 1mg${\times}$2, 1mg${\times}$2 ; Group 32) to induce double or triple ovulations. The cows of Group B1 and B2 were Inseminated artificially(A1) at following estrus. Twenty four heifers were bred by A1 and received an additional embryo into the uterine horn contralateral to the corpus luteum(CL) 6 days later(Group C). One embryo was transferred into each uterine hem of 16 heifers 6 days after estrus(Group D). Fourteen heifers were received two embryos into the uterine horn ipsilateral to the CL at day 6 of estrous cycle(Group I). Pregnancy rates at 60 days in Group A, B1, B2, C, D and E were 34.8％, 70.0％, 60.0％, 66.7％, 62.5％ and 57.1％, respectively. Twinning rates were 8.7％, 20.0%, 10.0％, 16.7％, 18.7％ and 21.4％, respectively. The present experiments demonstrate that FSH treatment( Group 31) and ipsilateral transfer( Group I ) of two whole-embryos are more useful methods to produce twins than the others.

• Journal of Conservation Science
• /
• v.34 no.5
• /
• pp.433-442
• /
• 2018

In this study, metal properties were compared by preparingthree iron knives from steel ingots produced via traditional iron-making, and ingot which jointed the steel of modern times. Metal microscope and SEM-EDS analysis revealed fine ferrite and pearlite structures of the hypo-eutectoid steel of Fe-C alloys. All samples also exhibited martensite on the blade of the knife. By Vicker's hardness analysis, the hardness of the sand iron knife (K1) was 533.38 HV, sand iron-nickel steel knife (K3) was 514.8 HV, and sand iron-carbon steel knife (K2) was 477.02 HV. The mass reduction due to wear was 0.058% for K1, 0.059% for K3, and 0.144% for K2. EPMA(Electron probe micro-analyzer) analysis of the surface pattern of the specimens confirmed that the patterns were exposed due to differences in the content of C or the chemical composition. Additional research on heat treatment processes is needed to increase the abrasion resistance of blades. Traditional steel ingots could produce high-quality steel if combined with nickel steel.

• Journal of Korea Foundry Society
• /
• v.41 no.2
• /
• pp.127-131
• /
• 2021

Based on its good compatibility with high-temperature environments, the Ti-48Al-2Cr-2Nb alloy is used for high-temperature materials of industrial equipment. In this study, a Ti-48Al-2Cr-2Nb alloy turbocharger turbine wheel was fabricated by a vacuum centrifugal casting method. The conditions that prevent misrun defects of the turbocharger turbine wheel blade from centrifugal casting using alumina molds were investigated. The microstructure of the alloy prepared by vacuum centrifugal casting was studied by means of optical microscopy (OM), with a micro-Vickers hardness analyzer (HV), by X-ray diffraction (XRD) and by SEM-EDS. The HV and SEM-EDS examinations of the as-cast Ti-48Al-2Cr-2Nb alloy showed that the thickness of the oxide layer (α-case) was typically less than 50 ㎛. At a high preheating temperature of 1,100℃, a moderate RPM of 260, and with an alumina mold with a large gate size, there were almost no misrun defects. Therefore, it was confirmed that a Ti-48Al-2Cr-2Nb alloy turbocharger turbine wheel with fewer misrun defects could be achieved through a high preheating temperature, a moderate RPM, a large gate size and an alumina mold to suppress the formation of alpha-case components.