A functionally graded material (FGMs) MoSi₂/Mo was adopted for oxidation resistance coating of γ-TiAl. The MoSi₂ coating was produced by dipping Mo plates in the molten salt. The obtained MoSi₂ coating layer resulted was approximately 60 μm in thickness. The oxidation resistance of MoSi₂/Mo was examined at 1323-1423 K for 3-400 h in still air, as a criterion for the lifetime of MoSi₂/Mo/γ-TiAl FGMs. The oxidation at 1423 K for 30 h in still air caused Si to diffuse into Mo without cracks or voids at MoSi₂/Mo interlayer. The MoSi₂ activation energy of volume diffusion was estimated as 523 ± 75 kJ/mol, which was consistent with the available data. The lifetime of the MoSi₂ coating was approximately five times larger than that of a NbSi₂ coating under the same condition. An oxidation-resistant MoSi₂/Mo FGMs coating has a longer lifetime than an NbSi₂/Nb coating for γ-TiAl.

It is difficult to determine precise electrochemical data and analyze corrosion behavior in dilute solution, because dilute solution is a high solution resistance environment. In order to solve these problems, it is necessary to establish an electrochemical measurement method to analyze corrosion behavior. In this study, we examined about electrochemical impedance spectroscopy and coupling current measurement which is a suitable electrochemical measurement method in a low-concentration electrolyte environment using pure zinc, pure iron and stainless steel type 304 (SUS304). In low concentration solution, it was found out that electrochemical impedance spectroscopy has to use two-electrode cell and coupling current measurement is effective method to analyze corrosion behavior. The charge transfer resistance of pure zinc is fixed in 0.0001—0.01 M NaCl solution and decreases in 0.01 M or more. That of Fe drastically decreases in 0.0001—0.001 M, mildly decreases in 0.001—0.5 M and increases in 0.5 M or more. That of SUS304 is fixed in all concentration. The coupling current decreases with decreasing of solution concentration. The reason of decreasing of coupling current is estimated that solution resistance increases by decreasing of solution concentration.

Abstract In this paper, the fracture problem of a functionally graded piezoelectric material strip (FGPM strip) containing a crack perpendicular to the interface between an FGPM strip and a homogeneous layer is considered. The problem is solved for the laminate that is suddenly heated from the surface of the FGPM strip. The surface of the homogeneous layer is maintained at the initial temperature. The crack faces are supposed to be completely insulated. Material properties are assumed to be exponentially dependent on the distance from the interface. By using the Laplace and Fourier transforms, the thermo- electro-mechanical fracture problem is reduced to a singular integral equation, which is solved numerically. The stress intensity factors are computed and presented as a function of the normalized time, the nonhomogeneous and geometric parameters.

Preciously, we suggested a novel heat-electric power conversion effect without temperature gradient. In this study, we purposed synthesizing sample for a novel effect with Spark Plasma Sintering (SPS). This effect needs joining n-type, intrinsic and p-type semiconductors. In addition, intrinsic semiconductor must have narrower band gap than n- and p-type semiconductors. Therefore, we payed attention to Ba₈Au_xSi_46-x for satisfying these requirements. Ba₈Au_xSi_46-x is changed its electrical properties by Au contents. Furthermore, this materials show that n- and p-type semiconductors show wider band gap than intrinsic semiconductor. In this study, we synthesized two layers sample of n-type and p-type Ba₈Au_xSi_46-x with SPS. Sintering process was expected promoting Au diffusing from p-type to n-type, and form a Au gradient part in n/p interface. According to results of WDX, chemical composition gradient was observed in n/p interface. This result showed that sample synthesized by SPS satisfied two requirements. Therefore, the sample was heated under uniform temperature and generated voltage showed 2.5 mV at 500°C. These results suggested SPS was suitable method for synthesizing samples of a novel effect.

A novel electric power generation different from the Seebeck effect by using poly-crystaline Ba₈Au_xSi_46-x clathrate consisted of two layers, n-type and p-type materials, was devised. In order to investigate composition dependence of generated voltage, poly-crystalline clathrate samples consisted of two layers with various Au composition were prepared by SPS method. According to composition analysis, the mixed layer was formed at the interface of two layers. The sample consisted of n-type Ba₈Au_4.5Si_41.5 / p-type Ba₈Au_5.5Si_40.5 can generate around 2.0 mV at 723 K under no temperature difference. It is considered that this voltage was caused by charge separation with the diffuse of electrons and holes exited at mixed layer with narrower band gap part on interface. Ba₈Au_4.0Si_42.0 / Ba₈Au_6.0Si_40.0 and Ba₈Au_4.8Si_41.2 / Ba₈Au_5.2Si_40.8 samples showed around 4.0 and 1.0 mV at 723 K, respectively. These results suggested that the voltage increased with difference of Fermi level between n- and p-type semiconductors.