Fumio Ogawa

In situ chemical vapor deposition of metals on vapor-grown carbon fibers and fabrication of aluminum-matrix composites reinforced by coated fibers

Aluminum, nickel, silicon, and titanium were deposited onto the surfaces of vapor-grown carbon fibers (VGCFs) using a simple and cost-effective in situ chemical vapor deposition method. This process began with the in situ reaction of metal powders and iodine in heated quartz tubes, leading to the formation of metallic iodide vapors. Aluminum was deposited by annealing at 500xa0°C, forming almost homogeneous metallic aluminum layers on VGCFs. Aluminum-matrix composites reinforced by aluminum-coated VGCFs were fabricated by powder metallurgy. The tensile strength of these composites was improved by the aluminum-coating treatment. Nickel was deposited by annealing at 600xa0°C. The coating layer consisted of grains smaller than 5xa0nm. Molten aluminum was dropped on sheets comprising nickel-coated VGCFs, and the contact angle was measured; the wettability was found to be clearly improved. Composites containing nickel-coated VGCFs were fabricated via hot extrusion of a mixture of Al–7Si alloy and VGCFs at semisolid temperature. Vickers microhardness values of the composites were improved by nickel-coating treatment because of improved interaction of the aluminum matrix and VGCFs at the interface. A metallic silicon-coating layer was formed by annealing at 1100xa0°C. For titanium coating, the reaction of VGCFs with titanium and conversion of the VGCF surface into titanium carbide was confirmed. In the case of titanium, metallic titanium could be deposited without the use of iodine.

Creep Characteristic of Sn1.0Ag0.7Cu Lead-Free Solders with Element Addition

In this study, creep properties of lead-free solders based on Sn1.0Ag0.7Cu were investigated. In the solders, germanium, nickel and bismuth were added to improve their mechanical properties. The effect of element addition on their microstructure and creep properties were studied. Creep properties were improved with the element addition. Creep rupture lifetime was the longest for SnAgCuBiNiGe, and that of SnAgCuBi was the second longest. It was made clear that a minimum creep strain rate is useful for lifetime prediction of the solders. An observation of microstructure was performed and coarsening of intermetallics after creep test was identified, resulting in creep rupture. It was found that the addition of bismuth hinders the coarsening of intermetallics and is effective to improve the creep properties of the solders.

Fatigue Testing and Evaluation of Fatigue Strength under Multiaxial Stress State; Why do we need fatigue testing?

Types of multiaxial fatigue tests and their experimental results are presented in this paper. There are typical three types in multiaxial fatigue tests: the combining push-pull and reversed torsion loading test using hollow cylinder specimen, the biaxial tension-compression test using cruciform specimen and the inner pressure applied the push-pull loading test using the hollow cylinder specimen. In the combining a push-pull loading and a reversed torsion loading test, failure life under non-proportional loading in which principal directions of stress and strain were changed in a cycle was shortened compared to proportional loading in which those are fixed. Fatigue lives were well-correlated using a non-proportional strain range considering the effect of strain path and material dependence. In the biaxial tension-compression test, the failure life decreased with increase of the principal strain ratio. In the inner pressure applied the push-pull loading test, cyclic deformation behaviour due to complex loading paths of multiaxial fatigue tests with the inner pressure associated with push-pull and rev. torsion acted to reduce the failure lives. Experimental investigation of multiaxial failure life and elucidation of their governing mechanism is essential and it can broaden the applicability of structural components.Cylindrical grinding is the process of metal removal using multiple cutting point. The objective of the study is to investigate the chip characteristics (shape and width) and surface roughness materials. The materials are AISI 1020, AISI 1045, AISI 1090, AISI D2, and AISI 4340 with a grinding wheels WA46K8V. The research is using cylindrical grinding processes at low-speed workpiece 100 rpm, depth of cut 0.5 mm, in dry condition. Result of research is comparing characteristic chip with variable feet rate 120 mm/min, 420 mm/min, 1300 mm/min. The result is to show the increasing feedrate lead, the growth of chip width and high surface roughness value. On materials AISI 1020, AISI 1045, AISI 1090, and AISI 4340 show that chips width is related to hardness value.

Thermal Conductivity and Tensile Properties of Carbon Nanofiber-Reinforced Aluminum-Matrix Composites Fabricated via Powder Metallurgy: Effects of Ball Milling and Extrusion Conditions on Microstructures and Resultant Composite Properties

Carbon nanofiber (CNF)-reinforced aluminum-matrix composites were fabricated via ball milling and spark plasma sintering (SPS), SPS followed by hot extrusion and powder extrusion. Two mixing conditions of CNF and aluminum powder were adopted: milling at 90xa0rpm and milling at 200xa0rpm. After milling at 90xa0rpm, the mixed powder was sintered using SPS at 560xa0°C. The composite was then extruded at 500xa0°C at an extrusion ratio of 9. Composites were also fabricated via powder extrusion of powder milled at 200xa0rpm and 550xa0°C with an extrusion ratio of 9 (R9) or 16 (R16). The thermal conductivity and tensile properties of the resultant composites were evaluated. Anisotropic thermal conductivity was observed even in the sintered products. The anisotropy could be controlled via hot extrusion. The thermal conductivity of composites fabricated via powder extrusion was higher than those fabricated using other methods. However, in the case of specimens with a CNF volume fraction of 4.0%, the thermal conductivity of the composite fabricated via SPS and hot extrusion was the highest. The highest thermal conductivity of 4.0% CNF-reinforced composite is attributable to networking and percolation of CNFs. The effect of the fabrication route on the tensile strength and ductility was also investigated. Tensile strengths of the R9 composites were the highest. By contrast, the R16 composites prepared under long heating duration exhibited high ductility at CNF volume fractions of 2.0% and 5.0%. The microstructures of composites and fracture surfaces were observed in detail, and fracture process was elucidated. The results revealed that controlling the heating and plastic deformation during extrusion will yield strong and ductile composites.

Low Cycle Fatigue Test of Lead Free Solders Using Small Sized Specimen

This paper investigates the fatigue results in low cycle fatigue region obtained from a miniaturized specimen having a 6mm gage length, 3mm diameter and 55mm total length. Fatigue tests were performed for two type lead-free solders using horizontal-type electrical servo hydraulic push-pull fatigue testing machine. Materials employed were Sn-3.0Ag-0.5Cu and Sn-5Sb. The results from Sn-3.0Ag-0.5Cu were compared with those obtained using a bulk specimen in a previous study. Relationship between strain range and number of cycles to failure of the small-sized specimen agreed with those of the bulk specimens. The testing techniques are applicable to Sn-5Sb following the Manson-Coffin law. These results confirm that the testing technique proposed here, using small-sized specimen, is suitable to get fruitful fatigue data for lead-free solder compounds.

Evaluation and visualization of multiaxial fatigue behavior under random non-proportional loading condition

In cyclic multiaxial stress/strain condition under nonproportional loading in which principal direction of stress/strain are changed in a cycle, it becomes difficult to analyze stress/strain ranges because of complexity of multiaxial stress/strain states depending on time in cycles. In order to evaluate stress/strain simply and suitably under non-proportional loading, Itoh and Sakane have proposed a method called as IS-method and a strain parameter for life evaluation under non-proportional loading ??NP. In the method, 6-components of stress/strain are converted to an equivalent stress/strain indicating the amplitude and the direction of principal stress/strain as a function of time as well as an intensity of loading nonproportionality fNP. Based on IS-method, the authors also have developed a tool which enables to analyze multiaxial stress/strain condition with the nonproportionality of loading history and evaluate failure life under nonproportional multiaxial loading. The tool indicates the analyzed results on monitor and users can understand visually not only variation of the stress/strain conditions but also non-proportionality during the cycle, which helps the design of material strength.