Unidirectional solidification of eutectics offers a simple, inexpensive approach to the production of composite materials. The authors and co-workers have studied the production of fiber strengthening composite materials by various methods. In this paper, an attempt has been made to prepare Al-Si eutectic fibrous composites by means of unidirectional solidification. The main results are follows:(1) In order to produce continuous structures of Al-Si eutectic alloys, it was found that solidification rate was less than 1.5 mm/hr by using four or five nine aluminum and semi-conductor-grade silicon as materials.(2) The cross section of silicon colonies showed four-fold symmetry and side branching, and individual silicon colonies extended over several millimeters in the growth direction. Wavy patterns of silicon phase were observed among straight silicon colonies in a cross section parallel to the growth direction.(3) The growth mechanism of Al-Si eutectics seemed to differ from that of lamellar and rod-like structures, as silicon had a highly preferred growth direction. So the two phases did not exhibit any consistent orientation relationship.(4) Impurities of materials have a considerable effect on the growth of silicon phases. So, if the factors which effect the growth of silicon phases is found, the shape of silicon colonies may be controlled, for example, by adding the third element to Al-Si eutectics.
The surfaces of Ti-Zr alloys before and after immersion in an electrolyte which contains inorganic ions found in the biological system were characterized using X-ray photoelectron spectroscopy (XPS), in order to know the changes in the surfaces of the system. Plates of Ti-25Zr, Ti-50Zr, Ti-60Zr, and Ti-75Zr alloys (in mass%) and metallic Ti and Zr were polished and immersed in the solution at 310 K for 3.6 ks (1 h), 86.4 ks (1 d), or 2.6 Ms (30 d) in sealed bottles. After immersion, the specimens were washed and analyzed using XPS. The XPS data revealed that the ratios of the relative concentrations of Ti to those of Zr in the surfaces were almost the same as those in the bulks. In the surface oxide layer, Ti and Zr were uniformly distributed along the depth direction. The thickness of the surface oxide of the alloys before immersion increased with increasing the Zr content in the alloys. The chemical state of Zr was stabler than that of Ti in the surface oxide layer. In surface layers of the alloys, mainly oxidation primary proceeded by the immersion and then hydroxidation occurred. Calcium phosphate was only formed on Ti-25Zr immersed for 2.6 Ms and metallic Ti whereas titanium phosphates and/or zirconium phosphates were formed under other conditions.
Rare earth magnets have corrosive problems associated with their use in prostheses in various fields including orthodontics. The purpose of this study is to investigate the corrosion behavior of an Nd2Fe14B magnet and a SmCo5 magnet in an oral environment. The relations among the attractive force changes, the released elements, the weight changes and the anodic polarization measurements of the magnets were examined under immersions in 1% NaCl, 1% lactic acid, 0.05% HCl, 0.1% Na2S and Greenwood's artificial saliva at 37 degrees C for forty-two days. The results showed that the rare earth magnets underwent high corrosive assaults and large attractive force reductions by the immersions in 1% lactic acid and 0.05% HCl. The problem of corrosion of the magnets could be overcome by sealing them within laser-welded stainless steel capsules.
Bending properties and thermal behavior of twenty commercial Ni-Ti alloy orthodontic arch wires were investigated quantitatively to characterize their suitability for clinical use. There was substantial difference among the load-deflection curves obtained by a three-point bending test. Some wires exhibited super-elasticity; load decreased little with decreasing deflection. Others showed good spring-back properties only; load was nearly proportional to deflection. Thermal behavior due to phase transformation of the alloy was examined by differential scanning calorimetry (DSC). Some of the wires did not have the correct transformation temperatures to exhibit super-elasticity at body temperature. Moreover, thermal behavior was closely related to super-elasticity. There were clear thermal peaks in the DSC curves of the super-elastic wires. However, wires without super-elasticity had no peak in the DSC curves.
