Phased array is a phase synthesis imaging technique developed in field of radar, and has been widely used in medical diagnosis using accurate acoustic imaging. Recently it became one of the core nondestructive inspection methods mainly for periodic inspection of nuclear power equipment. Here, we explain the control of the transmission sound field of ultrasonic phased array and also the aperture synthesis method in imaging processing of received signals. In addition, new equipment of SPACE (Subharmonic Phased Array for Crack Evaluation), which is the nonlinear ultrasonic flaw detection technique as the industrial application of Phased Array techniques, will be mentioned.
Ti alloys are widely applied to jet engine components. Low cycle fatigue (LCF) strength of Ti alloys decreases with tensile stress dwell at room temperature (Cold Dwell Fatigue, CDF). CDF strength was influenced by stress level, microstructure, and dwell time. In order to study the effect of long time dwell for CDF properties, LCF test (0s dwell), CDF tests (120s~7200s dwell), and creep test were carried out. With increase of dwell time, fracture cycle decreased and fracture elongation increased. Fracture surface of long time dwell CDF tests corresponded to that of creep test. Additionally, strain accumulations during stress dwell at long time dwell CDF tests were similar to strain change of creep test. From SEM/EBSD analysis, inelastic strain was obviously increased after CDF tests and creep test, compared to LCF test. Hence, it was considered that long time dwell CDF was greatly influenced by creep deformation.
In this study, a rapid oxynitriding technique based on induction heating was developed for the titanium alloy Ti-6Al-4V, and its effects on surface characteristics of the alloy were investigated. The surface microstructures of the alloy were characterized by employing a scanning electron microscope, electron back-scatter diffraction, X-ray diffraction and nano-indentation tests. Induction-heating in air for 60 s caused the formation of a hardened layer on the Ti-6Al-4V alloy surface, which can be attributed to the diffusion of oxygen and nitrogen atoms. When water quenching was performed after heating, transformation to an acicular martensitic α’ phase occurred, resulting in increased in substrate hardness. However, cracks were initiated at the surface of the oxynitrided alloy. The cracks were eliminated through fine particle bombarding treatment, whereas the hardened layer formed by the oxynitriding treatment remained. The obtained results thus indicate that the oxynitriding technique developed in this study can enhance the wear resistance and tensile strength of the Ti-6Al-4V alloy within a short period of time.
In this study, rapid debinding of alumina molded bodies was carried out using superheated steam at 1 kg / h to 5 kg / h. The superheated steam treatment was performed with a temperature increase of 10 °C / min to a holding temperature range of 600 °C to 800 °C. For the alumina molded body, the carbon removal rate increase in the case of debinding treatment with superheated steam amount of 3 kg / h to 5 kg / h compared with 1 kg / h of superheated steam. The molded body resulted in a carbon removal rate of 98.8 % after treated with superheated steam at 800 °C with 5 kg / h. No cracking occurred in alumina molded bodies obtained by debinding in superheated steam. However, cracks occurred in debindied bodies that had been treated in air under similar temperature conditions. No cracking occurred in sintered bodies obtained by debinding in superheated steam and then firing at 1,600 °C in air. However, many large cracks occurred in sintered bodies that had been treated in air or nitrogen under similar temperature conditions. Thus, it was suggested that superheated steam treatment is highly effective for rapid debinding of molded alumina bodies.
Thermal barrier coating (TBC) is a key technology for prolonging the life of the hot sections of gas turbine and airplane engines. A TBC system has a three-layered structure comprising a substrate, bond coat (BC), and TBC topcoat (TC). Young’s moduli and Poisson’s ratios of the coatings are important for calculating the parameters of material mechanics in the TBC system. However, research on Poisson’s ratio is scarce owing to the difficulty of its evaluation. The objective of this paper is to investigate the effect of high temperature exposure on Poisson’s ratios of yttria-stabilized zirconia TC and CoNiCrAlY BC. For this purpose, we evaluated the time-dependent Young’s moduli and Poisson’s ratios of coatings thermally treated at 600 °C to 1000 °C using the bending method. Our measurement revealed that an increase in Poisson’s ratios of the TC and BC as well as Young’s moduli depended on the temperature and length of exposure. The increasing rate in Poisson’s ratios was lower than that of Young’s moduli for both the TC and BC. These phenomena were explained by focusing on the microcracks and pores of the coatings.