Katsunori Inoue

Electrical conductivity of plasma-sprayed titanium oxide (rutile) coatings

Abstract Plasma spraying has been used to prepare n-type polycrystalline TiO2 coatings on SUS304 steel substrates. The influence of plasma spray process on the phases (corundum type Ti2O3, monoclinic Ti3O5, triclinic magneli phases, and tetragonal rutile) formed and the relation between deoxidation and the electrical conductivity of plasma-sprayed TiO2 coatings have been studied. The amount of oxygen loss in the plasma-sprayed TiO2 coatings is influenced greatly by the addition of hydrogen in the plasma gas. Accordingly, the electrical conductivity of TiO2 coatings increases with decreasing oxygen during plasma spraying. The amount of reduced TiO2 coating increases with a drop in pressure of the plasma spray atmosphere and an increase in the quantity of hydrogen. The amounte of Ti2O3 and Ti3O5 phases formed by plasma spraying increase with the deoxidation of TiO2 coatings.

Identification of void shrinkage mechanisms

A method for identifying void shrinkage mechanism experimentally is presented. We treat the void shrinkage on the bonded interface during solid state diffusion bonding of similar metals. The voids are arranged at regular intervals. The experimental results were analysed by log(T/ts) vs (1/T) and log ts vs log P plots, where T is the absolute temperature, P the compressive stress, ts is the time taken to attain the void shrinkage of a certain volume ΔV. We obtained ts by measuring a certain growth of bonded area ΔS replaced by ΔV. Even if ΔS is adopted, we can identify the transition of the dominant mechanism by slopes of those plots. As a result, interface self-diffusion, volume self-diffusion and power law creep were experimentally identified as fundamental mechanisms which contribute to the void shrinkage process during diffusion bonding of metals.

Numerical analysis of the interfacial contact process in wire thermocompression bonding

Wire deformation processes during thermocompression bonding without ultrasonic vibration are simulated by a numerical model which is based on the finite-element (FE) technique. The growth process of interfacial contact between wire surface and lead frame is also analyzed. If the contact interface is fixed, then the lateral wire surface expands simultaneously with folding to the lead frame, producing the perimeter bond. On the other hand, if the contact interface can slide, the center of contact area largely expands and the lateral wire surface does not extend, It follows that the interfacial contact area tends to be fixed, but does not slide when the perimeter bond is produced, even if a strong metallic bond is not achieved at the center. A wire reduction greater than 0.5 is required for ensuring the strong perimeter bond formation. This is supported by the experimental results. The interfacial contact area is governed mainly by the wire reduction. If the reduction is kept constant, then the tool with a groove increases the contact area somewhat larger than the flat tool, although the groove tool decreases the rate of wire deformation. We further discuss the size limit of wire bonding, taking into account the perimeter bonding mechanism.

Numerical analysis of fine lead bonding-effect of pad thickness on interfacial deformation

Deformation process of lead and pad during inner or middle lead bonding for packaging integrated circuit (IC) is simulated by a finite element method (FEM) in order to understand the effect of pad thickness on lead deformation behaviors, especially on the interfacial extension between lead and pad. The simulated bonding process was simplified so that we could easily understand the effect of pad thickness. Because of the simplification, we assumed that lead and pad were both made of gold and the cross section of lead was square. The mode of the interfacial deformation largely depends on the size ratio of /spl delta//sub 0//h/sub 0/, where /spl delta//sub 0/ is the pad thickness and H/sub 0/ is the lead height. The distributions of equivalent stress on the lead/pad and pad/substrate interfaces were also analyzed to discuss the bondability. It was suggested that the size ratio controls the position of the maximum stress at the pad/substrate interface which can damage silicon substrates.

Liquid-Mn sintering of plasma-sprayed zirconia-yttria coatings

Abstract The penetration phenomena of liquid Mn into porous ZrO 2 −8 wt .% Y 2 O 3 coating, plasma sprayed on JIS SS400 steel substrate was studied by heating at 1573 K in a vacuum atmosphere, and the possibility of improving the mechanical properties of the coating by heat treatment with liquid Mn was examined. It was found that liquid Mn rapidly penetrated the coating and formed an interface between the coating and the substrate. The densification of the coating occurred when ZrO 2 particles were sintered with liquid Mn that penetrated the porous ZrO 2 coating. It was revealed that the dense coating was free of porosities and that its hardness increased greatly after heat treatment with Mn, compared with as-sprayed ZrO 2 coating. Moreover the modulus of elasticity and the fracture toughness of the coating reached the same levels as those of sintered partially stabilized ZrO 2 (Y 2 O 3 ).

Three-dimensional reconstruction of cleavage fracture surface for duplex stainless steel

Abstract A reconstruction system of three-dimensional topography by parallax measurement of stereoscopic scanning electron microscopy has been developed. A digital elevation of the fracture surface was calculated from the relative displacement between corresponding positions using an area-based matching algorithm, and then digital elevation models of the three-dimensional topography were reconstructed on the monitor of a personal computer. The system was applied to the ductile fracture surfaces of duplex stainless steel. The reconstructed images obviously revealed an elongated dimple fracture originating from inclusions and cleavage cracks arrested by austenite grain. The reconstruction of the cleavage fracture surface of type 444 ferritic stainless steel was also made, and the elevation of cleavage steps of the river pattern was detected.

Optimisation of welding using two Nd–YAG laser beams combined at workpiece surface

Abstract Two Nd–YAG laser beams were combined at a certain point on the workpiece surface to increase weld penetration depth. One of the beams was a pulsed laser beam, and the other was a continuous wave laser beam or a modulated laser beam. Using this combination of laser beams, a wide range of welding conditions, such as average power, peak power, and power density, could be selected. A high peak power pulsed laser beam would play a significant role in forming a keyhole, but a severe spatter loss problem could be encountered under high peak power laser conditions, thus the conditions necessary to prevent spatter loss were investigated. The greatest penetration depth is obtained under the critical conditions for spatter loss. Critical conditions for spatter loss are controlled by the peak power of a pulsed laser beam, thus deeper weld penetration is obtained using a pulsed laser beam with higher average power, that is, of longer pulse width and/or a higher repetition rate within the limit of the oscillator output. Moreover, spatter loss is reduced under conditions providing large molten zones in the weld, thus a higher peak power pulsed laser beam can be employed under such conditions. Large molten zones are obtained using a modulated laser beam of a high average power and/or low welding speeds.

Numerical analysis of fine lead bonding-effect of pad mechanical properties on interfacial deformation

The present study was carried out for the purpose of understanding solid state inner and middle lead bonding, especially the effect of pad mechanical properties on the interfacial deformation processes between lead and pad based on a computer simulation that was carried out by using a finite element method (FEM). As the mechanical properties largely depend on temperature, we discuss the influence of temperature on the effect of pad mechanical properties, i.e., the pad temperature is different from the lead temperature. It is suggested that the interfacial extension reaches greater than 20% for only 10% lead reduction as the pad temperature is 200 K higher than the lead temperature. We further discuss the effect of the substrate temperature on the bond strength, based on the calculated and experimental results.

Application of laser flash method to penetrative materials for measurement of thermal diffusivity

AbstractThe theoretical equation for the laser flash method is derived where the penetration and transmission of the input energy into the test piece is taken into account. The thermal diffusivity of penetrative materials and its measurement errors are calculated instantly by fitting the experimental data to this equation by using the method of least squares with an on-line personal computer connected to the laser flash device. The usefulness of this method is shown by comparing it with the conventional method.

Penetration treatment of plasma-sprayed ZrO2 coating by liquid Mn alloys

The penetration phenomena of liquid manganese (Mn) alloy into porous ZrO2 (8 vvt % Y2O3) coating plasma sprayed on SS400 steel substrate was studied by heating in a vacuum atmosphere. The improvement in mechanical properties of the coating by heat treatment with liquid Mn alloys was examined. Liquid Mn alloys, such as Mn-Cu, Mn-Sn, and Mn-In, rapidly penetrated the coating and formed a chemical bond between the coating and the substrate. The densification of the ZrO2 coating occurred when ZrO2 particles were sintered with liquid Mn alloys that penetrated the porous coating. The dense coating was free of porosity, and its hardness increased after heat treatment with Mn alloys, compared with assprayed ZrO2 coating. Moreover, the fracture toughness of the coating reached the same levels as those of sintered yttria-stabilized PSZ.