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Volume 78, Issue 5
Displaying 1-6 of 6 articles from this issue
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Regular Article
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Shinichi Fujiwara, Reinhold H. Dauskardt2014 Volume 78 Issue 5 Pages 177-182
Published: 2014
Released on J-STAGE: May 01, 2014
JOURNAL FREE ACCESSIn previous research on copper wire bonding on a copper substrate with tin plating, suitable thickness and binding conditions for the tin plating were chosen using the peel test after the copper wire bonding. These conditions were determined to be a thickness of 10 μm, a stage temperature of 373 K, a bonding power of 500 to 700 mW and a bonding time of 30 to 50 ms. Cross-sectional observations of the bonding interface indicated that the tin layer remained between the copper wire and copper substrate after bonding under these conditions. The purpose of the present study was to evaluate the joint interface structure of the bonded copper wire on the copper substrate with the tin plating. Residual Sn exists locally at the initial bonding interface, and the locations bonded to the interstitial Sn are intermixed with the locations where the Cu wire is bonded to a Cu-Sn intermetallic compound. No oxide film layer was found at the bonding interface in the joint between the Cu wire and Cu-Sn intermetallic compound; TEM images indicated that these have metallic bonding in which Cu and Cu3Sn are directly bonded. This is in contrast to ultrasonic bonding between Cu and Sn, wherein the Cu and Sn are bonded by means of the Sn oxide film.
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Yoshikazu Tanabe2014 Volume 78 Issue 5 Pages 183-187
Published: 2014
Released on J-STAGE: May 01, 2014
JOURNAL FREE ACCESSThe crack energy density causes a new expression of fracture toughness for brittle fracture, together with the concept of Barenblatt's cohesive forces. The Griffith's formula for fracture toughness is modified by the ratio of σT/∑T, which σT is the true fracture stress and ∑T the maximum strength of the material obtainable by ordinary processing. The fracture toughness of elastic-plastic material, K*Ic for brittle fracture is described by the product of σT and the root of the observed absorption energy by Charpy impact test corrected for instrumental effect, √Icpcorrected. The characteristic distance dc depends linearly on the released elastic energy.
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Tatsuro Morita, Mikio Yamanaka2014 Volume 78 Issue 5 Pages 188-194
Published: 2014
Released on J-STAGE: May 01, 2014
JOURNAL FREE ACCESSThis study was conducted to investigate the effects of titanium-fine-particle bombarding (Ti-FPB) treatment on fatigue strength of friction-stir-welded aluminum alloy (FSW material) and on its mechanical properties in salt water environment. Fatigue cracks of Ti-FPBed FSW material were initiated from the root of the overhung weld toes formed by the passing of the tool, as well as those of FSW material. Ti-FPB treatment introduced compressive residuals stress to the surface of FSW material, although its absolute value was relatively low near the weld toes. As a result, fatigue strength of FSW material was recovered by Ti-FPB treatment to the same level of the substrate. Ti-FPB treatment diffused titanium to the surface of FSW material. Diffusion of titanium was insufficient near the weld toes because of disturbance by the overhung weld toes. Such insufficient diffusion of titanium induced electrolytic corrosion. As a result, tensile strength of FSW material in salt water environment deteriorated with Ti-FPB treatment.
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Makoto Hasegawa, Yosuke Oki2014 Volume 78 Issue 5 Pages 195-200
Published: 2014
Released on J-STAGE: May 01, 2014
JOURNAL FREE ACCESSFracture behavior and fracture toughness of metal particle dispersed alumina matrix composites are investigated. Ni, Ni-5Al and CoNiCrAlY particles are used for the composites. Volume fraction of the metal particles is ranging from 5 to 20 vol%. Microstructures before and after heat exposure are observed from the surface. Vickers hardness of the composites decreases with the increase in particle volume fraction. As for the composites before heat exposure, crack propagates at alumina/metal interface when the crack reaches to the particle. After heat exposure, crack mainly passes through the oxidized particle of the composites. The fracture toughness increases with the increase in volume fraction. In the same volume fraction, heat exposed composites show lower fracture toughness than that of the composites before heat exposure due to the oxidation of the metal particle which lowers the toughening potential of plastic dissipation from the metal.
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Yuri Iijima, Koji Kakehi2014 Volume 78 Issue 5 Pages 201-204
Published: 2014
Released on J-STAGE: May 01, 2014
JOURNAL FREE ACCESSIn this study, the effect of the addition of a low-melting element, Pb, on the mechanical properties of Inconel 718 was studied using another alloy, Alloy 718Pb, which contains more Pb than the Aerospace Material Specifications (AMS) limit. Tensile tests and creep tests at 650℃ were conducted. Pb did not affect any tensile properties, but it decreased the creep rupture life and creep rupture elongation of Alloy 718Pb. Segregation of Pb to the grain boundary was identified. We discuss the results in terms of the segregation effect of Pb to the grain boundary.
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Yoshihiro Nakayama, Koji Kakehi, Daisuke Kondo2014 Volume 78 Issue 5 Pages 205-210
Published: 2014
Released on J-STAGE: May 01, 2014
JOURNAL FREE ACCESSNi-based superalloys have excellent mechanical properties at high temperature. Such alloys, however, do not have good workability at their high temperatures because of the high strength. PM (powder metallurgy) has received attention as a possible way to solve this problem and improve yield rate. PM superalloys such as Rene95 and RR1000 have been in practical use as materials in the discs and blades of aero engines because their many advantages of homogeneous structure, mechanical properties and yield rate outweigh disadvantages such as cost of processes like producing alloy powder and HIPping (hot isostatic pressing). However, PPB (prior particle boundary) is known to decrease the toughness and ductility of PM alloys. The forging process is generally applied after sintering by HIP to crush PPBs, which are caused by impurities on the surface of the powder. The forging process is not, however, necessarily preferable after the HIP process, because near-net-shape manufacturing is an unique characteristic of the powder-sintering process. The PDR (thermal plasma-droplet-refining) treatment is known to capable of reducing impurities in refractory-metals powder. In this study, to reduce PPBs, PDR was applied to alloy 718 powder. The alloy powder was HIPed at a δ-subsolvus temperature to achieve a superfine grain and high strength. The influence of PDR treatment on tensile properties and the microstructure of P/M 718 were investigated. After PDR treatment, the impurities in the powder were reduced. The PDR treatment was found to increase the density of the sintered specimen. However, it did not improve ductility as expected due to an insufficient reduction of the oxygen content and fine precipitates in PPB.
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