Materials Science Forum Vols. 706-709

Abstract: Titanium and Ti alloys are widely used as substitutional materials for natural bone because of their good biocompatibility, high strength, and high corrosion resistance. In our previous studies, TiO₂ coating on Ti with Ra (arithmetical means of roughness) < 0.1 μm formed by anodizing had much higher osteoconductivity than that of pure Ti. It can be expected that TiO₂ coating with fine surface can improve the osteoconductivity of Ti alloys. In this study, the effects on the osteoconductivity of TiO₂ coatings on different kinds of Ti alloys were investigated by in vivo study. TiO₂ coatings with Ra < 0.1 μm were formed on 4 kinds of Ti alloys (Ti-6Al-4V (Ti64), Ti-6Al-7Nb (Ti67), Ti-29Nb-13Ta-4.6Zr (TNTZ), Ti-13Cr-1Fe-3Al (TCFA)) using anodizing in H₃PO₄ aqueous solution. Surface properties of these coatings were evaluated using SEM, XRD, and XPS. In in vivo study, samples were implanted in rats’ tibia for 14 days, and then removed. Cross section of the sample was observed with optical microscope and bone-implant contact ratio (R_B-I) at the interface between body tissue and bone was used as a parameter of osteoconductivity. Anatase type TiO₂ coatings with Ra < 0.1 μm were uniformly formed on all of the Ti alloys by anodizing at low voltage. These oxide coatings contained the ions of other alloy elements. TiO₂ coatings on Ti64 and Ti67 indicated high osteoconductivity similar to that of TiO₂ coating on pure Ti. On the contrary, TiO₂ coating on TNTZ and TCFA showed low osteoconductivity. It was thought that ions of alloy elements brought bad influence on the osteoconductivity of TiO₂.

Abstract: Electrophoretic deposition method has been developed for the fabrication of organic-inorganic composite films, containing bioglass and hydroxyapatite in a hyaluronic acid matrix. The film composition and deposition yield were varied by variation of the electrochemical bath composition and deposition time. The films were studied by scanning electron microscopy, thermogravimetric analysis and X-ray diffraction methods. The deposition method offers the advantages of room temperature processing and allows the fabrication of composite films for biomedical applications.

Abstract: Sometimes, there is a need for a material that has some properties of one polymer as well as some properties of another polymer. Instead of going back in to the laboratory and trying to synthesize a brand new polymer with all the needed

Abstract: High boron content Al-B₄C metal matrix composites are highly attractive as an excellent neutron absorber material for the storage of spent nuclear fuels. In the present paper, the mechanical properties of two composites with AA1100 matrix reinforced with 25 and 30 vol.% B₄C at ambient and elevated temperatures have been investigated. The thermal stability of two composites at 300°C is experimentally determined. The microstructural features and the tensile fracture at different conditions are examined. It is found that the mechanical properties of both composites remain unchanged at 300°C after a long holding period up to 1000 h. The thermal stability of the mechanical properties of the composites is directly related to the stability of all microstructural compounds of the material. Finally, the effect of the tensile temperatures on the fracture mechanism is assessed.

Abstract: Powder injection moulding of 304L stainless steel - tungsten carbide (WC) composites were carried out in the present work. Two different WC particle i.e. WC having average size of 4.8 µm and 1.6 µm were used. Feedstock of powder loading up to 55 vol% were successfully prepared using binder composed mainly of polyethylene glycol (PEG) and a minor constituent of polymethylmethacrylate (PMMA). The mouldings were leached in water at temperatures of 40 °C and 60 °C from 30 minutes to 24 hours in order to study the effect of leaching conditions on the removal of the PEG. The remaining binder, PMMA, provided strength to the mouldings after leaching of the PEG and it could be removed by pyrolysis during ramping up to the sintering temperature. Specimens were sintered under hydrogen atmosphere at 1250 °C for 1 hour. Sintered components were subjected to testing and characterisation. Scanning electron microscope was used to observe microstructure of specimens after moulding, leaching and sintering. It was found that the hardness of the sintered specimens increased with either increasing the amount of the powder loading in the feedstock or reducing the average size of WC in the powder mixture. In addition, the water leaching of the PEG linearly correlates with the natural log of time and the equation predicts that PEG will be removed completely in 11.24 ± 1.31 hours which corresponds with the experiment result that PEG completely removed in 12 hours.

Abstract: The demand for new materials in medicine is on the increase today. Long-lasting implants (joint prostheses, dentistry implants), made typically of metals and their alloys, are characterized with high mechanical properties, however their corrosion resistance and biocompatibility are relatively low. One of the methods to ensure particular functional properties is to employ composite implants, combining improved mechanical properties of metallic material with biocompatibility of ceramic materials. The study aimed to develop and analyse properties of metallic/ceramic composites made of the mixture of powders: austenitic steel (316LHD) and ceramics (Al₂O₃).

Abstract: Carbon fiber-reinforced plastics (CFRP) composite is most attractive materials to reduce the weight of transportations. To increase the production volume and the efficiency in the field of CFRP component, fast, highly precise and cost-efficient technologies are required. Although laser cutting meets these requirements, it is not used because of insufficient knowledge about the effect of thermal damage on the material behavior. In this study, the effect of several cutting processes on the static tensile strength and the fatigue strength was evaluated for CFRP consisting of thermoset resin matrix and carbon fibers. The CFRP was cut using two different-type of lasers; a CO₂ gas laser and a single-mode fiber laser, an abrasive water-jet and a conventional mechanical tool. The mechanical cutting specimen produced a cut of high quality. The water-jet cutting specimen showed a moderate quality though was seen a trace of abrasive grain. While, the laser cutting specimens clearly showed a heat-affected zone (HAZ). The static tensile strength and the fatigue strength by laser cutting specimens clearly decreased in comparison with mechanical or water-jet cutting specimen. The laser cutting specimen exhibited a linear dependency of the tensile strength on the HAZ, indicating that the main effect resulted from thermal destruction of CFRP within the HAZ.

Abstract: In this work, porous TiB₂ ceramics were consolidated by pressureless sintering method using metallic Ti and Fe as additives in order to perform sintering at temperatures lower than 1700°C. It was shown that processing parameters including milling time of the starting mixture had a considerable effect on final properties of sintered specimens and their behavior in molten aluminum. Microstructural studies were carried out using optical microscope, SEM and EPMA. It was found that specimens with uniform and crack-free microstructure could be produced using the pre-mixed powders milled for as low as 30 min prior to compaction and sintering. Sessile drop test was performed on the specimens milled for 30 and 240 minutes. Their interaction with molten aluminum was also studied. It was found that 30 min milling time resulted in better electrical conductivity, wettability and stability in liquid aluminum.

Abstract: Metal-bonded diamond grinding wheel was fabricated by a centrifugal mixed-powder method. The centrifugal mixed-powder method is a novel and effective casting process to obtain functionally graded material (FGM). At the beginning, we performed fundamental experiments using Al-Si alloy system for the purpose of knowing the migration behavior of mixed-powder under centrifugal force. Al-Si hypereutectic alloyed-powder or mixed-powder of Al and Si particles was placed into the mold, and then Al molten metal was cast under a centrifugal force. Cross sectional microstructure observation and quantitative analysis of Si content were conducted using an electron probe microanalyzer. Amount of Si decreased with receding from a mixed-powder region. Si concentration gradient in the sample fabricated Al-Si powder was smaller than the one fabricated using mixed-powder of Al and Si particles. Subsequently, φ 20 mm Cu/diamond grinding wheel was fabricated by the casting method. Graded diamond distribution was successfully obtained.

Abstract: MgB₂ has the higher critical temperature of superconducting transition (T_C : 39K) among the intermetallic compound superconductive materials, however, MgB₂ is hard for practical use because of its unworkable and lower critical current density (J_C) in a high magnetic field than Nb-based superconductive materials. We have developed the original method of three-dimensional penetration casting (3DPC) to fabricate the MgB₂/Al composite materials. In the composite material we made, MgB₂ particles dispersed to the matrix uniformly. Thus, these composite materials can be processed by machining, extrusion and rolling. The T_C was determined by electrical resistivity and magnetization to be about 37～39K. In this work, we made composite material with ground MgB₂ particle with the purpose of extruding thinner wires of composite material, successfully produced φ1mm wire and changed the matrix from pure Al to Al-In alloy. J_C of composite materials with the matrix of Al-In alloy was calculated from the width of the magnetic hysteresis based on the extended Bean model. The result was better than that of MgB₂/Al composite material without Indium. Microstructures of these samples had been confirmed by SEM observation.