Materials Science Forum Vols. 510-511

Abstract: ZrO2-SiO2 coatings deposited on 316 L stainless steel were prepared to protect chemically the substrates by sol-gel process using Zr(OC3H7 n)4/Si(OC2H5)4 as precursors. The influence of the ZrO2-SiO2 coatings on the corrosion resistance of the 316 L stainless steel was evaluated with the potentiodynamic polarization curves in deareated 15% H2SO4 solutions at 25, 40 and 50 °C . Comparative test was performed on uncoated one. The values of the electrochemical parameters explain how. ZrO2-SiO2 films increase the resistance of stainless steel against corrosion.

Abstract: UV nano imprint lithography (UV NIL) that uses a monomer based UV curable monomer resin is proposed as a method of imprinting at low temperature and pressure. The fabrication of high fidelity patterns on a topographical substrate is a formidable challenge. To accomplish this, the use of bi-layer nano imprint lithography, which involves the use of an easily removable under-layer and an imprinted pattern, is proposed. We hypothesized that by etching the under layer by oxygen RIE, we might be able to build the bi-layer patterns for easy lift-off and fabricate nano-sized metal patterns through this lift-off process.

Abstract: The morphological evolution and growth mechanism of solidification interface with solidification rates were investigated in the Ni-base superalloy, IN738LC, by directional solidification and quenching technique under a relatively high thermal gradient of 20.5oC/mm. The planar interface of the MC-γ eutectic was found at the low solidification of 1 µm/s, and the dendritic interface formed above 5 µm/s. The dendrite lengths increased as increasing increasing solidification rate, and the dendrite tip temperature was close to the liquidus temperature at 50 µm/s. The carbide morphologies were blocky-type and rod-type in the planar interface of low solidification rates, and as the solidification rate increased, the carbide shape changed from script type to spotty type. The phase transformation temperatures from the dendrite to MC carbide and eutectic were estimated by DTA and by the solid/liquid interface morphology by directional solidification.

Abstract: Growth behavior of thermally grown oxide (TGO) layer with thermal fatigue condition in thermal barrier coatings (TBCs) was investigated, including its effect on fracture behavior of TBCs and bonding strength of top coat. The formation of TGO layer was influenced by both temperature and time exposed. However, the TGO thickness was independent on the bond coat thickness (80, 140, and 280 µm) and the preparing method (APS and HVOF methods) of the bond coat. In Hertzian indentation tests for the TBCs before thermal fatigue, the TBCs with the bond coat prepared by APS showed fracture and/or delamination in regions of the top coat near to the interface, whereas the TBCs prepared by HVOF indicated cracks and fracture at the interface. After thermal fatigue, the fracture path passed along the TGO layer without any cracks created from Hertzian indentation within the top coat in both cases. The bonding strength of the top coat measured by adhesion tests shows lower values for the TBCs with the HVOF bond coat than those with the APS bond coat before thermal fatigue. However, the values are similar to each other after thermal fatigue. This result is attributed to the fracture path of the TBCs, depending on the TGO formation.

Abstract: Directional or single crystal technique was applied to enhance the ductility, and two phases of γ (Ni) phase or β (NiAl) phase in γ‘(Ni3Al) matrix were also considered to increase the strength and ductility. In this study, directionally solidified rods were prepared at the solidification rate of 50µm/s in 23-27 at.% Al-Ni alloys, and tensile strengths of these rods were analyzed at room temperature. Directionally solidified samples showed the γ dendrite fibers formed in the Ni3Al matrix in the hypo eutectic composition of 23 at.% Al, the γ‘ single phase in the eutectic composition of 24.5 at. % Al, and the β dendrite fibers in the γ‘ matrix in the hyper eutectic compositions of 25, 26, 27 at.% Al. The hypoeutectic alloy including γ dendrites with γ‘ matrix exhibited a large elongation of over 70% with ductile transgranular fracture at room temperature. With increasing Al contents, the γ dendritic microstructure changed to the β dendrite in the γ‘ matrix, which resulted in decreasing the elongation by increasing the volume fraction of the brittle β dendrites in the ductile γ’ matrix.

Abstract: The fabrication of nano-structured materials using nanoimprint lithography has become more prevalent in recent years, due to its cost effectiveness and readiness. However, One of the biggest drawback of this technique is the fabrication of the imprinting stamp, which is expensive and difficult to fabricate. This paper describes a method of replication original Si or quartz made imprinting template into a polymer stamp which has many advantages, such as the simplicity and low cost of the fabrication process and the flexibility of the resulting stamp. Using the hot embossing method, PVC based imprint stamp with sub 100nm patterns can be fabricated. Due to its high UV transmittance, reasonable mechanical hardness and low surface energy, PVC based nanosized template can be used as a stamp for UV-NIL and sub 100nm patterns were successfully transferred by the UV-NIL process with PVC based imprint stamp.

Abstract: Iron(Fe)-molybdenum(Mo) alloyed nanopaticles and nanowires were produced by the chemical vapor condensation(CVC) process using the pyrolysis of iron pentacarbonyl(Fe(CO)5) and molybdenum hexacarbonyl(Mo(CO)6). The influence of CVC parameter on the formation of nanoparticle, nanowire and size control was studied. The size of Fe-Mo alloyed nanoparticles can be controlled by quantity of gas flow. Also, Fe-Mo alloyed nanowires were produced by control of the work chamber pressure. Obtained nanoparticles and nanowires were investigated by field emission scanning electron microscopy, transmission electron microscopy and X-ray diffraction.

Abstract: Carbon nanotubes (CNTs) were grown on 304 stainless steel using iron as a catalyst. By using the applied voltages of 4-6 kV, iron wire with 0.5 mm in diameter was sparked for 1, 2, 10 and 100 times to form catalytic dots on the steel substrate. CNTs were subsequently grown in a gas mixture of 10 ml/s Ar and 0.1 ml/s C2H2 at a temperature range 700 - 900 K for 300 s (5 min). The dots and CNTs were characterised using AFM, SEM and TEM to determine their characteristics.

Abstract: During the sintering process, the onset of abnormal grain growth is depend on various factors. The abnormal grain growth behavior, however, was focused only the growth stage compared to nucleation stage. Because most of abnormal grain growth occurred to a rapid mode, the observation of abnormal grain growth was impossible. In this study, we intend to in-situ observe the nucleation stage of abnormal grain using porous alumina. As a result, the liquid phase due to unintended impurities plays a main role for the formation of abnormal nuclei by the rearrangement of small grains due to the capillary force.

Abstract: In this study, the effect of MgF2 additive on the mechanical properties of hydroxyapatite (HAp)/zirconia composites was investigated. As a fluoride additive, MgF2 was added to HAp/zirconia composites for the suppression of phase decomposition from HAp to tricalcium phosphate (TCP). Due to the dissolution of MgF2 at the phase decomposition temperature of HAp, the phase decomposition of non-stoichiometric HAp was suppressed. When MgF2 (5, 10 vol%) was added to HAp/zirconia composites, the decomposition of HAp was completely suppressed below 1400oC due to the ion substitution F- of for OH- in the HAp crystal structure. The flexural strength and Vickers hardness of composites was revealed more higher values compared with the MgF2-free composites.