Key Engineering Materials Vols. 345-346

Abstract: Adhesion strength for single layer ceramic capacitor sheet, used in MLCC(Multilayer Ceramic Capacitor), was measured by peel tests. The peel strength was measured during the separation of the ceramic sheet from the PET film using the peel testing system developed in this study. The sheet specimen was adhered on the glass jig floating on the liquid media, which was designed to minimize the friction, and the specimen was pulled up by micro-actuator. In this study, the dependency of the specimen width, peel angle and testing speed on the adhesive strength was experimentally investigated. It was found that the adhesive strength for the ceramic sheet is nearly identical, irrespective of the specimen width ranged from 5 to 20 mm, and the adhesive strength was increased with increasing testing speed. Furthermore, the strength was shown to be dependent on the peel angle.

Abstract: An evaluation method for adhesive bending and shear strengths between microsized components and silicon substrate were developed to quantitively determine micro-sized adhesive strength for micro-electro mechanical system (MEMS) devices. Cylindrical shape is employed as a micro-sized adhesive specimen to simply analyze adhesive stresses of both shear and bending. Micro-sized adhesive tests between micro-sized SU-8 cylindrical specimen and Si substrate were performed using a mechamical testing machine for micro-sized material that has developed by our group. Delamination of all the specimens occurred within the SU-8 near by the substrate in a brittle manner under both bending and shear loading conditions. The adhesive bending stress is 57 % lower than the bend strength of the SU-8 material. The adhesive shear strength under bend loading is 15 % lower than the adhesive strength under shear loading and the delamination surface is different in each loading mode. All the results suggest that some defects at the interface must induce the stress concentration, which may make the apparent strength of SU-8 decrease.

Abstract: In recent years there have been vast efforts to establish organic electronic devices. A key property of such devices is the possibility to fabricate them on flexible substrates. As the layers are mechanically stressed during bending, the knowledge of mechanical properties of the materials used will become very important. In this research the mechanical properties of the intrinsically conductive and widely used polymer PEDOT/PSS were investigated using a micro tensile test setup. The tensile tests showed values for Young’s Modulus in the range from 1 GPa to 2.7 GPa, for the tensile strength in a range from 25 MPa to about 55 MPa and for the total strain at break between 3% and 5%, all of them depending on relative humidity.

Abstract: Femtosecond laser is a perfect laser source for materials processing when high accuracy and small structure size are required. Due to the ultra short interaction time and the high peak power, the process is generally characterized by the absence of heat diffusion and, consequently molten layers. Various induced structures have been observed in glasses after the femtosecond laser irradiation. Here, we report on space-selective precipitation and manipulation of noble metal nanoparticles in the femtosecond laser-irradiated glasses.

Abstract: The abutment screw loosening of dental implant system has been remained problem in restorative practices. Surface treatment of screw plays a role of preventing screw from loosening in implant screw mechanism. The purpose of this study was to investigate surface characteristics of ZrN and TiN coated dental gold-screw and Ti-screw by ion-plating method and to evaluate wear resistance, surface roughness, and film adhesion on the screw surface using field emission scanning electron microscopy(FE-SEM), energy dispersive x-ray spectroscopy(EDX), micro-diamond scratch tester, vickers hardness tester, and surface roughness tester. The surface of gold screw and GoldTite is more smoothly than ones of other kinds of non coated screw. The ZrN and TiN coated surface is more smoothly than ones of other kinds of screw. The hardness of TiN and ZrN coated surface showed higher than that of non coated surface. The TiN coated titanium screw and ZrN coated gold screw have a good wear resistance and adhesion on the surface. The surface of ZrN coated screw showed low surface roughness compared with the surface of TiN coated screw.

Abstract: Copper reinforced by tungsten particles has high potential applications in the fields of electronics and electric contacts where high strength accompanied with good electrical conductivity is required. The effects of different scaling parameters (deformed volume, tungsten volume fraction and the tungsten particle size) affect the force needed for the machining of the W/Cu particle reinforced composites. W/Cu composites with different weight percentages of tungsten (80, 70 and 60 wt.%) were tested under compression loading. Different sizes of the compression specimens were tested; the specimen diameter DS was varied to be 1, 2, 4, 6 and 8 mm. The effect of the tungsten particle size was varied to be 10 and 30-m. The compression tests were done at strain rates of 0.1s-1. The experiments were carried out within a temperature range from 20 °C to 800°C. The mechanically tested specimens were metallographically investigated to determine the degree of deformation of the tungsten particles in different specimen geometries. A clear dependence of the flow stress on the volume of the deformed specimens and the tungsten volume fraction was found. This size effects were more obvious with increase of the tungsten volume fraction at lower temperatures. The metallographic investigation was helped to understand the observed size effect of the composites in relation to the volume fraction and the specimen size

Abstract: Porous-surfaced with solid core Ti-6Al-4V implant compacts were fabricated by traditional powder metallurgy. Powder metallurgy technique was used to produce three different porous surfaced implant compacts 30, 50, and 70% in vacuum atmosphere. The solid core formed in the center of the compact shows similar microstructure of near full density of Ti-6Al-4V. The compressive yield strength was up to 270 MPa and significantly depended on the surface porosity, core size, and temperature of sintering. Selected porous-surfaced Ti-6Al-4V implant compacts with a solid core have much higher compressive strengths compared to the human teeth and sintered fully porous Ti-6Al-4V joint replacements. The ingrowth of bone tissue into the outer porous surface layer results in part fixation, while the solid inner core region provides the necessary mechanical strength for a device used for the replacement of heavy load bearing joint regions such as the hip and knee. The microstructure of sintered samples was investigated.

Abstract: The aim of this study is to establish the net-shape forming of titanium matrix composites (TMCs) shot sleeve for Al alloys die-casting using a casting route. In-situ synthesis and casting of TMCs were carried out in a vacuum induction melting furnace. The synthesized (TiC+TiB) TMCs were examined using an scanning electron microscopy and electron probe micro-analyzer. The thermo-physical variables estimated by casting process were applied to the modeling of TMCs shot-sleeve casting using the Magmasoft®. The results of the investment casting and modeling of TMCs confirm that the casting route can be an effective approach for the economic net-shape forming of TMCs shot sleeve.

Abstract: The use of fiber reinforced polymer (FRP) bars has been gaining increasing popularity in the civil engineering community due to their favorable properties such as high-strength-to-weight ratio and good corrosion resistance. In order for concrete to be FRP reinforced, there must be interfacial bond between FRP bars and concrete. The interfacial bond behavior of FRP bars to concrete is expected to vary from that of conventional steel bars, since various key parameters that influence bond performance are different. This paper presents the results of an experimental and analytical study on the interfacial surface interaction of glass fiber reinforced polymer (GFRP) bars in high strength concrete cube. The experimental program consisted of testing 54 concrete cubes prepared according to CSA S802-02 standard 1). The split specimens showed that interfacial bond failure of the steel bar occurred due to concrete crushing in front of the bar deformations, while interfacial bond failure of the GFRP bars occurred partly on the surface of the bar and partly in the concrete by peeling of the surface layer of the bar.

Abstract: TiAl alloys Al composition range between 45 and 49 at%, includes γ-TiAl and α2-Ti3Al, are an emerging high temperature materials which has higher specific strength, oxidation ratio and specific modulus than Ni base superalloy. In this study, TiAl alloys were manufactured by plasma arc melting (PAM) and then TiAl and granular boron carbide were in-situ synthesized in PAM method again. The in-situ synthesized TiAl matrix composites were investigated by using X-ray diffractometer, optical microscope, and electron probe micro-analyzer.