Solid State Phenomena Vols. 124-126

Abstract: One of the most important use of thermal spray coatings is for wear resistance. In this work, the tribological properties of plasma prayed Al83.7Fe7Cr6.3Ti3 quasicrystalline coatings have been studied. The quasicrystal powders of Al-base alloys were produced by gas atomization unit in vacuum. The plasma spray process was used to produce quasicrystalline coatings. Then, friction experiments were carried out on a pin-on-disc-type tribometer. The results indicated that the friction coefficient of Al83.7Fe7Cr6.3Ti3 quasicrystalline coating is about 50% lower than that of Al70Fe13Cu10Cr7 quasicrystalline coating.

Abstract: ALDC8 alloy was often corroded with form of intergranular corrosion in corrosive environments. Thus in order to improve its corrosion, the effect of annealing to corrosion resistance and hardness was investigated with parameters of heating temperatures such as 100°C, 200°C, 300°C, 400°C and 500°C for 1hr. Hardness was slightly decreased with annealing, especially, the decreasing of hardness was remarkably revealed in annealing temperature at 300°C. Corrosion potential was shifted to noble direction, and both AC impedance at 10m㎐ and polarization resistance on the cyclic voltammogram was also increased with annealing. Intergranular corrosion was not nearly observed at annealing temperature of 400°C, 500°C. Therefore the optimum annealing temperature for corrosion resistance as well as mechanical property is thought to be 400°C or 500°C.

Abstract: Binary transition metal nitride films have excellent tribological properties but these binary systems are still inadequate for high temperature applications due to their low oxidation temperature. Above 700°C, formation of porous oxides at the film surface deteriorates their mechanical properties rapidly by the. Especially impact and indentation resistance of these films deteriorate very quickly. In order to overcome these problems, Al based Al1-xCrxN films with X=0.29 and X=0.69 were synthesized by closed field unbalanced magnetron sputtering with vertical magnetron sources and their chemical composition, crystalline structure, morphology and mechanical properties including impact and indentation resistance were investigated. Synthesized Al1-xCrxN films formed solid solution showing FCC B1 type structure with strong (111) preferential orientation and films with X=0.29 showed a superhard hardness value of approximately 41GPa while films with X=0.69 did approximately 31GPa. While there was insignificant difference between Al1-xCrxN films with X=0.29 and X=0.69 in terms of Rockwell C indentation resistance, much improved impact resistance could be observed from the Al1-xCrxN films with X=0.29.

Abstract: This paper presents a simulation method on shielding effectiveness(SE). The method is completely general and able to optimize shielding materials. We found a sandwich structure that it can efficiently shield plane wave, using this simulation method. The relationship of film thickness and its skin depth was investigated in this study. Two-dimensional curves and three-dimensional graphs were calculated by tri-layer SE formulas. A sandwich structure, which is 3μm iron-brass-iron films, is capable of excellent shielding properties: the SE is between -73dB and -100dB in the frequency range of 1MHz~10MHz. Another sandwich structure with 12μm thickness of brass-iron-brass films can offer -680dB shielding attenuation. Simulation experiments indicate that sandwich films with diamagnetic and ferromagnetic layers have outstanding contribution on SE.

Abstract: The effect of Si on phase transformation was well known in dual phase steels. Si promoted the ferrite transformation and the enriched C in untransformed austenite prohibited the transformation at intermediate temperature range resulting in the formation of lower bainite and martensite at low temperature range. In addition, during continuous cooling with fast cooling rate, it was very hard to differentiate one phase from the others. In order to clarify the effects of Si on the austenite-to-ferrite transformation quantitatively, the start temperatures of bainite(BS) and martensite(MS) as well as ferrite(Ae3) and pearlite(Ae1) were calculated by thermodynamic analysis. LVDT measured by dilatometer and 1st differentiation peaks of LVDT were examined with microstructures, which gives a possibility of the phase separation. In CCT diagrams, it was also found that large austenite grain size(AGS) widened the gap between the transformation start(Ts) and end(Tf) when Si was added.

Abstract: The characteristics, such as electron temperature and the electron density, of CF4/Ar discharge in 2.45GHz microwave has been investigated by using a Langmuir probe with the microwave power and position. The results showed that the electron temperature and the electron density decrease with increasing distance from the plasma source. Increasing power enhances the dissociation and ionization of gas, and increases the electron densities. The electron temperature was decreased by reducing the mean free path of electrons with increasing microwave power. The electron temperature is 7.63 ~ 2.49 eV, and the electron density is 0.85×1011 ~ 4.3×1011 cm-3. From obtained electron energy distribution function, we known that high energy electron decreased with increasing microwave power and distance from the plasma source. The generated plasma by developed our system has good quality as results of Debye length λD = 35.8 ~ 67.3 μm, and Ln(ND) = 33.4 ~ 35.2.

Abstract: An ab initio study was carried out on interface energies at coherent interfaces between bcc Fe and MXs (NaCl structure, M = Ti, Zr, Hf, V, Nb, Ta, X=C, N). The interface energies have positive values for carbides and nitrides of group IVB metals (Ti, Zr, Hf), while they have negative values for carbides and nitrides of group VB metals (V, Nb, Ta). Influence of bond energy was estimated using the discrete lattice plane/nearest neighbor broken bond (DLP/NNBB) model. It was found that the dependence of interface energy on the type of carbides and nitrides was closely related to changes of the bond energies between Fe, M and X(=C, N) atoms before and after formation of the interfaces Fe/MX.

Abstract: In this study, the degree of the substitution of Cr3+ and Cr6+ into the ettringite structure has been investigated to extent the immobilization potential of ettringite in the field under specific conditions. Aqueous suspension containing calcium hydroxide, alumium sulfate, CrCl2(trivalent chromium) and CrO3(hexavalent chromium) was subjected to ultrasound irradiation under atmospheric pressure to investigate their effects on synthesis of Cr-ettringite. In the result, the substitution of Cr3+ into Al site takes place in ettringite structure in solution with Cr3+, and monosulfate/friedel’ salt phase is also formed by occurrence of extra Al ion in solution. However, in the case of Cr6+, owing to a higher affinity of sulfate anion to form ettringite than that of Cr6+,
most of Cr6+ did not substituted into the crystal structure of ettringite.

Abstract: This study combined microscratch test and fracture-mechanical analysis to assess the interfacial reliability of Nafion and Pt/Ru catalyst layers in micro fuel cells. Scratch test was used to determine the critical load for interfacial failure, while fracture-mechanical analysis was used to quantify the adhesion between Nafion (the electrolyte polymer substrate) and Pt/Ru alloy (catalyst coating). We also proposed a key of solving ambiguous problems in indentation cracking test by determining geometric information from crack propagation and critical points, as for a hard porous coating on a soft substrate. A comparative analysis of three coating methods, spray, decalcomania and their mixed process, was done to assess the validity of our new method.

Abstract: New method for evaluation of heat transfer coefficient is proposed. In general, many researchers have been studied about inverse problem in order to calculate the heat transfer coefficient on three-dimensional heat conduction problem. But they can get the time-dependent heat transfer coefficient only through inverse problem. In order to acquire temperature-dependent heat transfer coefficient, it requires much time for numerous repetitive calculation and inconvenient manual modification. In order to solve these problems, we are using the SQP(Sequential Quadratic Programming) as an optimization algorithm. When the temperature history is given by experiment, the optimization algorithm can evaluate the temperature-dependent heat transfer coefficient with automatic repetitive calculation until difference between calculated temperature history and experimental ones is minimized. Finally, temperature-dependent heat transfer coefficient evaluated by developed program can used on the real heat treatment process of casting product.