Materials Science Forum Vols. 539-543

Abstract: Bend and shear tests were used to characterize the improvement in impact behavior of various ultrahigh carbon steel laminated composites. These tests turned out to deliver much more useful information about the mechanical properties of the laminates than the Charpy impact tests and were especially interesting for characterization of laminates of very high toughness values. The toughness of the various laminates was controlled by the rolling conditions that determined the quality of the bond and the appearance of delamination by the interfaces. The bend test allows determination of yield and maximum stresses, absorbed energy and permits graphical visualization of layer fracture and delaminations as testing proceeds. The shear test allows mechanical characterization of the bond quality between layers, permitting prediction of possible delaminations, and therefore, the mechanical properties of the layered material.

Abstract: In this presentation, we show some experimental results of binder-free WC with Nano WC sintered by Pulsed Electric Current Sintering (PECS) process also known as Field Assisted Sintering Technology (FAST). The particle size of WC powder is almost 80 nm. These binder-free WC have extremely hardness and stiffness. However, these mechanical properties are dependent on the sintering condition, e.g., maximum temperature, applied presssure, etc. We show some relationship between mechanical properties and sintering condition to improve to sinter the binder-free WC

Abstract: Polymer composite materials, as advanced materials have been widely used worldwide, especially in the advanced technology field, due to their outstanding properties. Nowadays, a growing attention has been paid to the environmental corrosion failure of composites. Since it is environment related corrosion, the test parameters selected were temperature, humidity and ultraviolet. Among all the environmental factors, the temperature, especially acts with humidity, is the most affective factor. In order to get detailed information, the weight gains of the samples tested were measured regularly during the test. By the comparison, it can be seen that the water absorption rate had been affected remarkably due to the salt existence or the temperature change. The observation of the sample microstructure showed that there were many holes on the surface, indicating that the surface of the samples was destroyed by the test, and that there were some interactions between the surface layer and the absorbed component. It is that only the effect of temperature and humidity was discussed in this paper, the effect of the rest environmental factors will be discussed in following paper.

Abstract: The strain dependence of the critical current, Ic, of Bi2223/Ag/Ag-alloy composite superconducting tapes has been studied both experimentally and analytically under bending deformation for two types of tape used in the VAMAS bending round-robin program (classified as VAM1 and 3). Our former analysis showed that the experimentally obtained Ic values were between the calculated ones based on a damage-free initial state and a case where delamination occupied the full width of the tape mid-plane. The experimentally obtained Ic values were explained by the delamination occupying partial width of the tape mid-plane. However, the microscopic observation indicated that the delamination location in the thickness direction was not limited to the mid-plane. In the present study, the analysis was modified to incorporate the movement of the delamination location in the thickness direction. The calculated Ic values with delamination increased when the delamination location moved to compressive side of the tape, and decreased when that moved to tensile side of the tape. Finally, the experimental Ic values can be understood by the distribution of delamination in both width and thickness direction.

Abstract: Mg-based composites are fabricated through mechanical alloying (MA) the Mg65Cu20Y10Ag5 amorphous alloy spun and mixed with 1-5 vol.% spherical nano-sized ZrO2 particles in the planetary mill, after then formed by hot pressing in Ar atmosphere under different pressures at the temperature 5 K above the glass transition temperature (Tg). The microstructure characterizations of the resulting specimens are conducted by means of XRD, FEG-SEM, and TEM techniques. It is found that the nano-sized ZrO2 dispersed Mg-based composite alloy powders can reach to a homogeneous size distribution (about 80 nm) after 50-hour mechanical alloying. After hot pressing of these composite alloy powders under the pressure of 1100 MPa at 409K, a 96% dense bulk specimen can be formed. Throughout the MA and hot pressing, the amorphous nature of the Mg65Cu25Y10Ag5 matrix is maintained. The hardness of the formed bulk Mg-based composites (with 3 vol.% nano-sized ZrO2 particles) can reach to 370 in Hv scale. In addition, the toughness of the formed bulk Mg-based composites presents an increasing trend with the content of nano-sized ZrO2 particles and can reach to 8.9 MPa m .

Abstract: In situ TiB whiskers reinforced Ti metal matrix composites have been fabricated by spark plasma sintering (SPS). Microstructure and stacking faults of in situ TiB whiskers in the composites were investigated in detailed by means of scanning electron microscopy (SEM), transmission electron microscopy (TEM) and high-resolution electron microscopy (HREM). The TiB whiskers exhibit a hexagonal shape at the transverse section and grow along the [010]TiB direction. The crystallographic planes of the TiB whiskers at transverse section are always of the (100), (101) and (10 1 ) planes. The interfaces between the in situ TiB and Ti matrix are clean and faceted along (100)TiB side. However, small lateral growth steps are observed along (101) and (10 1 ) planes of TiB. The stacking faults in TiB whiskers are typically with a stacking fault plane of (100)TiB and displacement vectors of 0.5a±0.254c. The formation mechanism of stacking faults has been proposed and verified by HREM observations.

Abstract: Soft magnetic composites (SMC’s) are produced compacting iron powder coated with a thin insulator and then heat-treating the greens. In this study, to improve magnetic properties of SMC’s, formation of heat resistant MgO insulation layer on iron powder particles was examined. It was found that the MgO coating can be made by a dry process with two steps, i.e., oxidation of the iron particle surfaces and reduction of iron oxide by magnesium vapor. The SMC fabricated from the MgO-coated powder exhibits high resistivity even after heat treatment at 600
, which leads to low iron losses comparable to those of the as-punched silicon-iron laminations. This can be ascribed to complete relief of stress introduced in the compaction process.

Abstract: The effect of natural mica on the morphology and properties of polyamide 6 (PA-6) nanocomposites was examined. Natural mica (sericite) acquired from a well-known mine in Shimane, Japan was ion-exchanged with an alkyl amine hydrochloride compound. The resulting organomica was extruded with PA-6 using a twin-screw extruder. Quantitative analysis of TEM photomicrographs of the nanocomposite reveal a fairly large average particle length and a higher degree of platelet exfoliation for the natural mica-based nanocomposite compared to the clay version, thus translating into a higher particle aspect ratio. The resulting nanomica/PA-6 composite exhibits a high degree of mica exfoliation and improved thermal mechanical properties.

Abstract: To simplify forming process of cladding materials with high performance, such as copper cladding aluminum composite materials, and to improve the interface quality of cladding materials, a novel forming process called Core-Filling continuous Casting (CFC) for bimetal composite materials is proposed. A conceptual equipment is developed, and the forming of composite bars of copper cladding aluminum is investigated. The basic technique theory of CFC, the reaction and bonded state of interface and the interfacial bonding strength of the cladding materials, as well as the influences of technological parameters are analyzed. The composite bars of copper cladding aluminum with 24mm in diameter of core material and 8mm in thickness of cladding layer are successfully fabricated. The results show that: (i) the proposed CFC process is feasible in principle; (ii) the composite bars of copper cladding aluminum having metallurgical bonding interfaces can be fabricated by CFC process under the conditions of liquid copper temperature of 1250~1300°C, liquid aluminum temperature of about 700°C and drawing velocity of 12~24mm/min; (iii) the copper layer thickness distribution is uniform both in the directions of portrait and circumference and (iv) the interfacial bonding strength is higher than that of core aluminum.