발간논문

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The present study is concerned with the improvement of hardness and wear resistance in (TiC,Cr3C2)/carbon steel surface composites fabricated by high-energy electron beam irradiation. Three kinds of powder mixtures, i.e., 50TiC- 50MgF2(flux), 50Cr3C2-50MgF2, 25TiC-25Cr3C2-50MgF2 (wt.%), were placed on a plain carbon steel substrate, which was then irradiated with electron beam. In the specimens fabricated with flux powders, the surface composite layer of 3.0-3.2 mm in thickness was successfully formed without defects, and contained a large amount (up to 10 vol.%) of TiC or Cr7C3 carbides in the matrix. The hardness and wear resistance of the surface composite layer were directly influenced by hard carbides, and thus were about five to ten times greater than those of the steel substrate. Particularly in the surface composite fabricated with TiC and Cr3C2 powders, the wear resistance was most excellent because the hardness of the carbide and martensitic matrix was very high.

keyword : surface composite, high-energy electron beam irradiation, plain carbon steel, carbide

In order to evaluate the thermal creep properties of the zirconium alloy for nuclear application as fuel cladding, the creep test for the four types of the zirconium fuel cladding tubes which had different compositions was carried out by the internal pressurization method in the temperature of 400℃ and the hoop stress range from 100 to 150 MPa. Creep tests were performed up to 200 days, which showed the steady-state secondary creep rate. From the results of the creep test for the four types of the zirconium cladding tubes, the creep strain of those fuel claddings was gradually increased with increasing applied stress regardless of alloy composition. The alloying elements such as Sn, Nb were more effective in the creep resistance than other elements such as Fe, Cr, Mn and Cu, since the solubility of Sn and Nb in a-zirconium was higher than other elements. Therefore, to increase the creep property of the zirconium alloy it is necessary for the control of the alloying elements which have larger soluble limit in a-zirconium.

keyword : creep, zirconium, fuel cladding, alloying elements, final annealing

In this study, the effect of intergranular ferrite volume fraction on the hydrogen delayed fracture (HDF) resistance of high strength boron-added steel was investigated. For this purpose, constant loading test using cathodically charged specimens was conducted on the three intergranular ferrite volume fractions, i.e., 000, 6% and l0%. With the increase of the amount of intergranular ferrite volume fractions, the HDF resistance in boron-added steel was increased. TEM and SEM observations revealed that the intergranular ferrite took the carbides nucleation sites at grain boundaries, and as a result, the crack nucleation sites were reduced. And the result of thermal desorption analysis showed that the grain boundaries were the main trapping sites.

keyword : high strength boron-added steel, hydrogen delayed fracture resistance, intergranular ferrite, constant Loading test, thermal desorption analysis

Composite coatings were prepared by co-depositing fine particles of metallic or non-metallic compounds with the metal matrix. With a newly developed nano powder, the nano particles strengthened composite coatings are increasingly attracting scientific and technological interest by virtue of their high hardness, lo friction coefficient and total inertness to any acid or other chemical attack. Among these ultra fine particles, ultra dispersed diamond particles are increasingly attracting considerable scientific and technological interest. However, commercially available powders of detonation nano diamond are complex conglomerates consisting of discrete levels of aggregation. In this work, experiments have been carried out to study the effect of ultrasonic treatment time on the mechanical properties and surface morphology of the electroless Ni-P/nano diamond(ND) composite coating. The results show that the nano-particles are uniformly distributed in the composite coating, and the microstructure of the composite coating is much finer and denser compared with the pure Ni plating.

keyword : composite coating, pure Ni plating, nano-diamond, ND, aggregation, ultrasonic treatment time, mechanical properties

Effects of 85℃/85%RH(T/H) treatment conditions on the interfacial fracture energy of inkjet printed Ag/Polyimide system are investigated from 180° peel test by calculating the peeling deformation energy of peeled metal and polyimide films. Interfacial fracture energy between inkjet printed Ag and polyimide was initially around 28.0 g/mm, while the increase in T/H treatment times as 76, 196, and 388 hrs lead to initial increase up to 78.9 g/mm and then decrease to 56.4 and 44.3 g/mm, respectively. Ag-O-C bonding formation seems to be responsible for interfacial adhesion improvement in the initial T/H treatment while moisture penetration inside polyimide itself seems to be related to the decrease in interfacial adhesion for longer T/H conditions.

keyword : adhesion, temperature/humidity, peel test, inkjet printed ag, polyimide

For applications such as non-volatile FRAM, atomic-scale smooth surface of the substrate is necessarily prerequisite to realize epitaxial film growth resulting in sharp interface and high quality film. The objective of this article is to fabricate the SrTiO3 (STO) (111) substrate with well defined terrace structure and finally to evaluate the effecs of terrace on the growth of epitaxial Bi4-XLa-XTi3O12 (BLT) thin films. Buffered HF (BOE) solution was successfully applied to terrace formation of STO (111). Compared with BLT films grown on as-received substrate, BLT films on the substrate with well-defined terrace revealed apparently much better surface roughness and coherent interface between BLT film and STO (111) substrate. In addition, the c-axis of the BLT film was aligned identically with the STO [001] direction by applying terrace structure. Therefore, step-terrace structure is a crucial factor for the determinination of the structural properties of epitaxial BLT films.

keyword : SrTiO3 (111), Bi4-XLaXTi3O12, BLT, terrace, AFM, TEM

The dry sliding wear tests were performed on A356/20vol.% SiCp composites against semi-metallic pad materials. The samples were tested by pin-on-disc wear test equipment with different applied load and sliding velocity. The wear properties of A356/20vol.% SiCp against semi-metallic pad have exhibited good results with low wear rate even at the 700N applied load and 4.0 m/s sliding velocity and low friction coefficient in the range of 0.2-0.3. Wear behavior was examined through the observations and analysis of the worn surface, worn subsurface and wear debris. It is revealed that the oxide powders and carbon transferred from the counterpart formed on the worn surface and acted as lubricant to reduce the wear rate. In addition, platelike wear debris has been formed on the worn surface. The platelike wear debris is formed due to the plastic flow and increase of temperature on top of the worn surface.

keyword : aluminum, silicon carbide. composites. dry sliding wear, semi-metallic pad