No abstract

No abstract

Green composites composed of long maize fibers and poly ε-caprolactone (PCL) biodegradable polyester matrix were manufactured by the thermo-mechanical processing termed as 'Sequential Molding and Forming Process' that was developed previously by the authors' research group. A variety of processing parameters such as fiber area fraction, molding temperature and forming pressure were systematically controlled and their influence on the tensile properties was investigated. It was revealed that both tensile strength and elastic modulus of the composites increase steadily depending on the increase in fiber area fraction, suggesting a general conformity to the rule of mixtures (ROM), particularly up to 55% fiber area fraction. The improvement in tensile properties was found to be closely related to the good interfacial adhesion between the fiber and polymer matrix, and was observed to be more pronounced under the optimum processing condition of 130 • C molding temperature and 10 MPa forming pressure. However, processing out of the optimum condition results in a deterioration in properties, mostly fiber and/or matrix degradation together with their interfacial defect as a consequence of the thermal or mechanical damages. On the basis of microstructural observation, the cause of strength degradation and its countermeasure to provide a feasible composite design are discussed in relation to the optimized process conditions.

We developed a new lead-free solder alloy, an Sn-Ag-Cu base to which a small amount of Ni and Ge is added, to improve the mechanical properties of solder alloys. We examined creep deformation in bulk and through-hole (TH) form for two lead-free solder alloys, Sn-3.5Ag-0.5Cu-Ni-Ge and Sn-3.0Ag-0.5Cu, at elevated temperatures, finding that the creep rupture life of the Sn-3.5Ag-0.5Cu-Ni-Ge solder alloy was over three times better than that of the Sn-3.0Ag-0.5Cu solder at 398 K. Adding Ni to the solder appears to make microstructural development finer and more uniform. The Ni added to the solder readily combined with Cu to form stable intermetallic compounds of (Cu, Ni) 6 Sn 5 capable of improving the creep behavior of solder alloys. Moreover, microstructural characterization based on transmission electron microscopy analyses observing creep behavior in detail showed that such particles in the Sn-3.5Ag-0.5Cu-Ni-Ge solder alloy prevent dislocation and movement.

Characterization at the ceramic top-coat/metallic bond-coat interfacial region was conducted for several kinds of the plasma sprayed thermal barrier coating (TBC) systems by means of a transmission electron microscope (TEM), an electron probe micro-analysis (EPMA) and so forth, in order to find out the optimum compositional and structural conditions of the coating components together with the optimum coating processing condition for designing the advanced TBC systems. Specimens with different coating features were prepared systematically by using different coating parameters such as the top-coat spraying conditions and reheat-treatment conditions. Especially, the reheat-treatment was applied to the TBC specimen with different temperature either in air or in inert argon (Ar) gas atmosphere. It was found that in the case of reheattreatment in air the thermally grown oxide (TGO) was developed at the interface as multiple oxide layers; one is Al 2 O 3 layer developed discontinuously at directly above the bond-coat and another is the mixed oxides layer consisting of the Al, Cr, Co, Ni oxide particles on the Al 2 O 3 layer. Such a TGO layer was heterogeneous and imperfect layer with containing many kinds of defects. On the contrary, the TGO layer formed by the reheat-treatment in Ar was composed dominantly of the continuous and fairly purified Al 2 O 3 layer with large grain size and homogeneous layer thickness. The growth mechanism and influencing factors for TGO were discussed in some detail on the basis of the nanocharacterization and quantitative evaluation of TGO.