Advanced Materials Research Vols. 26-28

Abstract: The reliable reproducibility of nano patterns or other nano structures is one of many issues in the nano-imprint lithography process. An important prerequisite for reproducibility is suitable adhesion properties of adhesion promoters or anti-sticking layer. In this study, rhombus shaped symmetrical probe with a flat tip was developed and fabricated using MEMS fabrication technique. For the experimental setup of the adhesion test using a UV curable PAK01 resin coated AFM tip with several adhesion promoters, the flat tip is covered by PAK01 resist using micromanipulator. Anti-sticking layers of silane agents were prepared on the tip by vapor deposition method. Adhesion force between various adhesion promoters (GPTS, APMDS, APTS, DUV30J, O2 planairzation) and PAK01 resist and the force between anti-sticking layer (FOTS, DDMS) and PAK01 resist were evaluated using the force-distance mode of AFM. Adhesion force of GPTS and FOTS are about 7180 nN and 1660 nN, respectively.

Abstract: Mechanical behavior of small size materials has been explored due to many industry applications such as MEMs and semiconductors. The accurate measurements for mechanical properties of thin films are very challenge due to several technical difficulties. The proposed solution is the Visual Image Tracing (VIT) strain measurement system coupled with a micro tensile testing unit, which consists of a piezoelectric actuator, load cell, microscope and CCD cameras. This system has shown advantages of real time strain monitoring during the test and ability to measure the Young’s modulus, yiled strength and Poisson’s ratio of the material. Free standing Au films 0.5, 1 and 2 μm thick with average grain sizes of 104, 148 and 219 nm prepared by sputtering were studied using VIT system. The yield stresses of the films are dependent on film thickness and grain size.

Abstract: The low cycle fatigue tests of SA508 Gr.1a low alloy steel in 310oC deoxygenated water were conducted to investigate the effect of cyclic strain rate on the environmentally assisted cracking (EAC) mechanisms. The flattened striations and the blunt crack tip, which indicate the occurrence of the slip dissolution/oxidation, were mainly observed for the specimen tested at 0.008 %/s. On the other hand, the brittle cracks and the blunt main crack with microcracks, which are the evidences of the hydrogen-induced cracking (HIC), were observed for the specimens tested at 0.04 and 0.4 %/s. Through this study, it is thought that the slip dissolution/oxidation dominantly contributes to the reduction in the fatigue life at a strain rate of 0.008 %/s and the HIC is mainly responsible for the reduction in the fatigue life at strain rates of 0.04 and 0.4 %/s.

Abstract: The effect of the processing conditions of dolomite powders on the antiviral activity was studied against H5N3 avian influenza virus. When dolomite was fired in the ambient atmosphere, it decomposed into MgO and CaO by two stages at different temperatures, namely into MgO+CaCO3 at ca.1010 K and MgO+CaO at ca. 1070 K. Strong antiviral activity was observed after the complete decomposition into CaO and MgO. However, when the firing temperature exceeded 1673 K, the antiviral activity was degraded. It was also found that the degraded antiviral activity was recovered by sever ball mill grinding.

Abstract: The effect of the temperature and microstructure on the fatigue crack growth behaviors of two microstucturally different AISI type 347 stainless steel(SS)s are studied at reactor operating temperature conditions. From the results, it was observed that the fatigue crack growth rate(FCGR) of type 347 SS increased as the test temperature was increased. However, its temperature sensitivity was reduced when the ΔK was large. The measured FCGRs for both TP347-LP and TP347-HP at 25oC and 345oC were lower than those presented in the ASME code. Especially near the threshold region, the trend curve in ASME code overestimated the FCGR of type 347 SS when compared with the obtained data. Even though the effect of the microstructure on the macro-crack growth rate was not significant during stage 2, the differences between threshold values for the specimen with a high precipitate density and the one with a low precipitate density were observed. It is assumed that these differences in the precipitate density, which resulted in a difference in mean free path length of dislocation movement, are the source of the difference in ΔKth of type 347 steels.

Abstract: In the nuclear power plants (NPPs), wall thinning of the piping materials is generally caused by a flow-accelerated corrosion (FAC) and leads to a rupture with no warning unless it is detected and repaired in a timely manner. To reduce the FAC, it is better to use low-alloy steels, such as 1Cr-½Mo and 2¼Cr-1Mo, having higher FAC-resistance than carbon steel. Meanwhile, in the secondary water chemistry at the NPPs in Korea, hydrazine concentration is maintained within the range of 100~150 ppb. For applying these low-alloys to a piping material, we investigated the influence of hydrazine concentration on their FAC. An experiment was carried out at pH25°C of 9 controlled with ammonia in a deoxygenated aqueous solution containing 0~250 ppb-hydrazine by using a FAC test loop at 250°C for 300 hours. Experimental weight loss showed a hydrazine concentration dependency of the FAC in this concentration range, giving minimum at 150 ppb.

Abstract: Carbon nanotubes and carbon nanowires were synthesized by ethanol catalytic combustion (ECC) technique, using FeCl3 solution as a catalyst precursor. Applying the 0.01 mol/l, 0.1 mol/l and 1 mol/l FeCl3 as catalyst precursor solution to the copper plate, carbon nanotubes and carbon nanowires were synthesized. The effect of concentration on growth and structural changes of the as-grown nanomaterials are illustrated and discussed. This technique has advantages of low cost, large scale production and flexible reaction conditions, etc. This technique can be used to synthesize carbon nanotubes and nanowires on metal substrate directly. This technique also has potential applications for fabricating nano-electrical devices.

Abstract: The demand for ultra supercritical (USC) power plants has increased due to the need for high thermal efficiency and reduced CO2 emissions. For turbine materials, high-cycle and lowcycle fatigue life at USC service temperatures are needed to verify material integrity due to the heat-up and cool-down process of power plant operation and due to turbine variations during operation. In this paper, fatigue characteristics for 9~12 Cr steels as candidate USC bucket materials were investigated. First, the fatigue life between DS2B2 and COST B2 steel were compared. COST B2 is the commercial steel with improved high temperature properties by adding boron, and DS2B2 is the new steel developed by Doosan by adding Co and adjusting Mo and W based on the same Mo equivalent value (%wt. Mo + 1/2 %wt. W). DS2B2 steel was found to have longer low cycle fatigue life than COST B2. Second, the effect of boron on fatigue life for bucket materials based on COST B2 steel was investigated. At room temperature, as boron content increased, low cycle fatigue life became superior, whereas, at 593oC the fatigue life was similar. For high cycle fatigue, as boron content increased, fatigue life increased due to the strengthening effect by the addition of boron.

Abstract: In this research, corrosion fatigue tests using tensile strength of 490MPa TMCP steel were performed in synthetic seawater condition to investigate the corrosion fatigue crack propagation characteristics. The influence of cathodic protection at -800mV vs. SCE on the corrosion fatigue crack propagation behavior was investigated. Relationships between da/dN versus ΔK for the material were obtained by two types of test specimens. In the present study, F(α,β) versus α(= 2a/W) relationship for the CCT specimen was calculated by J integral approach, while that for the CT specimen was determined from ASTM E647. It is found that the fatigue crack propagation rate of TMCP steel in synthetic seawater condition is faster than that in air condition at least twice. Also, it is observed that the fatigue crack propagation rate of steel with cathodic protection is in between those of seawater condition without cathodic protection and air condition.

Abstract: Reliability evaluation of the welded structure is divided by method concentrating on defect and mechanical property. Thermal power plant facilities are operated in high temperature, high pressure and called for safety guarantee. Three factors are constituted for this. The First is PSI(pre-service inspection) and the second is ISI(in-service inspection) and the third is quantitative analysis in safety. Main steam and hot reheat steam pipes in thermal power plant are frequently making a trouble because of unsuitable quality control under construction. So, the suitable construction and the development of life forecast method is urgent matter. Therefore, the continuous indentation technique is interested in effective test method of pipes in power plant facilities. This strong point of the continuous indentation technique is possibility of super-precision measurement, programmed test analysis, nondestructive stiffness evaluation. This study is focused on the possibility of the continuous indentation technique application in main steam and hot reheat steam pipes for stiffness evaluation in thermal power plant facilities.