Recent trend of chromium (VI)-free coated steel sheets for electrical appliances are reviewed. Despite the large amount of research of chromium-free coating being carried out for many years, there have never been products that could provide excellent corrosion protection with a low cost treatment. Recently, in response to the increasing demands for ecological products, new chromate-free coated steel sheets were industrialized in Japan in 1998. Those products were adopted for chassis and cases of audio-visual and office equipment. Finally, features and practical characteristics of one of the new products are to be introduced.
The erosion and wear characteristics were investigated experimentally in Ti-Ni base alloys, which have the superior thermomechanical properties and the high corrosion resistance. The erosion tests were conducted by the method, which collides the compressed water of the high temperature and high pressure with the specimen. The erosion, which is caused by a combination of the cavitations and the shear stress due to the high-speed hot water flow, can be evaluated by this method. Furthermore, the sliding tests were performed at a constant sliding speed and sliding distance of 16.7mm/s and 50mm, respectively. Specimens were Ti-50at%Ni and Ti-45at%Ni-5at%X (X: Ag, B, Fe, Nb, Pb), made by an arc melting method and a plasma sintering method, and a Co-based alloy (Stellite 6) was used as a reference material. Influences of additional elements and hardness on the erosion resistance were investigated by observations of damaged surface and evaluating the maximum damaged depth and the damaged cross-sectional area. Furthermore, the effects of additional elements on wear were also investigated in relation to the specific wear rate and hardness. Results show that the Ti-Ni base alloys have higher erosion resistance than that of Co-based alloy and the Ti-Ni-Ag alloy fabricated by plasma sintering has high wear resistance equivalent to Co-based alloy.
A new Thermal Barrier Coating (TBC) system aiming superior thermal shock resistance and low cost, was developed upon combination of HVOF (JP-5000) sprayed CoNiCrAlY bond coating and Water Plasma Sprayed (WPS) yttria-stabilized zirconia top coating for application to industrial gas turbines. This TBC system was evaluated by thermal cyclic test. The new coating system of WPS/JP-5000 showed excellent thermal shock resistance compared to conventional APS (air plasma-spraying)-TBC system against thermal cyclic test condition of 1, 000°C-RT in air. Also the new coating method was confirmed to have good thermal shock resistance even for thick zirconia top coating layer. The superior thermal shock resistance of WPS/JP-5000 coating system was due to formation of microcrack in the top coating layer by WPS. In addition, the CoNiCrAlY bond coating by JP-5000 had a diffusion zone in between the sprayed particles and the substrate similar to VPS coating layers. The new TBC system of WPS/JP-5000 for application to industrial gas turbines is considered promising because its good thermal shock resistance and low cost.
It is very important to assess component materials such as concrete structures with non-destructive techniques. An acoustic impact method takes advantages of an easy handling and low costs in many other non-destructive techniques. Fourier spectrum, which was obtained by a fast Fourier transform of detected waves was examined for the evaluation of artificial defects formed on the square concrete samples. The effects of a striker and a detector on the Fourier spectrum were discussed to detect defects and their positions in the specimen. Vibration mode analyses were attempted to clarify the cause of the many peaks of frequency in the Fourier spectrum. It is found that the peak frequency, its amplitude and half-power bandwidth of the frequency spectrum can be indicators for detecting the artificial defect. The results suggested that this acoustic impact method using a steel ball as a striker and a microphone as a detector was fairly useful as one of non-destructive techniques for the assessment of concrete structures.
Dynamics and susceptibility of austenite/ferrite dual phase stainless steel plate of 1.5mm thickness to delayed fracture were studied by the wave-front simulation of Lamb wave AEs (Acoustic Emissions) and generation frequency, respectively. Ferrite area ratio of the steel increased from 56% at as-received specimen to 81% at heat-treated at 1423K. Attenuation of the first So-mode Lamb wave of as-received specimen was so large that the Lamb wave can not be detected, but decreased with an increase of ferrite phase. Susceptibility to the delayed fracture or AE event counts by micro-fractures increased in the order of as-received specimen, heat-treated specimen at 1073K, 1273K and 1423K. Micro fractures progressed underneath the surface of thin plate through both the ferrite and austenite grains. Source waves for heat-treated specimens, obtained by the waveform simulation of the first arrival So-packet of Lamb wave AEs, revealed fast small fracture in ferrite grains and slow large fracture in austenite grains.