Numerous research efforts have evidenced that the solder joint profile in SMT affects reliability of the joint. In this work, the three-dimensional solder joint profile of the J-lead is predicted by minimizing the energy due to surface tension and gravity. Geometric complexity stemming from the curved shape of the J-lead is resolved by employing a transformed coordinate and corresponding element types with the geometric continuity condition in the finite element formulation. Based on the simulation results, the solder volume and pad length are found to have significant effects on the solder joint profile. The predicted solder joint profiles show reasonably good agreements with experimental data when the solder volume is adjusted by the amount of the volume loss due to wicking.

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The effect of friction welding condition on initial joining phenomena and mechanism in 1st and 2nd phases of friction welding were investigated with continuous drive type friction welding machine, using mild steel.
The results are as follows ;
1) The initial joining location moved from the axial center part to the outside part of the specimen with the increase of friction pressure, when friction pressure was low. However, its location was constant, when friction pressure was high.
2) The initial joining start time increased with the decrease of friction pressure, when friction pressure was low but its time was not very much change, when friction pressure was high.
3) The location of traces and maximum temperature in faying surface agree with initial joining location.
4) The friction torque values on the 1st and 2nd phases were in proportion to the contact area in faying surface.
5) It was considered that the mechanism of movement of initial joining location by the friction pressure was caused by the movement of the location of plastic deformation with the increase of temperature in faying surface and heat conduction of the axial center part.

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In brazement with nickel filler metal, the formation of brittle phase degrades the reliability and the strength of the joint. This phase is composed of melting temperature depressants in the filler metal, such as silicon, boron or phosphorus. In particular, this phase tends to form in brazed joint with a wide clearance. In order to avoid the formation of the brittle phase, a strict control of brazing clearance is required, which is kept as narrow as possible during the brazing process. In some cases, however, such a strict control may be difficult.
The purpose of this study is to develop the filler metals free of or less in silicon, boron and phosphorus, thereby suppressing the formation of the brittle phase. The nickel-copper alloy was chosen as the bass alloy of the filler metal, and two kinds of Ni-Cu-Sn-Si and Ni-Cu-Mn-Si filler metals were developed. The experiments were carried out to investigate the mechanical properties of the joints brazed with these filler metals.
The tensile test of butt joints of SUS316 stainless steel brazed with developed filler metals was conducted, whose clearance were in the range of 10 to 100 micrometers. Hardness distributions of the brazed joints were also measured. Same experiments were carried out on the brazed joints with BNi-2 and BNi-5.
The tensile strength of the Ni-Cu-Sn-Si filler brazed joints was about 500 MPa for the clearance of 10μm and was about 300 MPa for 100μm. In the joins with the Ni-Cu-Mn-Si filler metal, the tensile strength was about 600 MPa for 10μm and 350 MPa for 100 μm. In the joints of clearance more than 50 μm, tensile strength of the developed filler metals were superior to those of BNi-2 and BNi-5, in which the hardness of the joints increased obviously.

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Some brazing filler metals containing titanium were brazed to sapphire plates under some brazing conditions, in order to investigate the cause of discoloration at the brazed surface. The differences of discoloration at the brazed surface were observed with a video-microscope from the reverse side of the brazed plane, and the brazed sapphire surfaces were examined by SEM after removing the brazing filler metals by dissolution using nitric acid and hydrofluoric acid. According to the SEM observation of brazed surfaces, the discoloration at the brazed surface increased with the increase of surface roughness caused by erosion of sapphire. The Brilliant-cut rubies were brazed to metals at the pavilion area under some brazing conditions with different erosion depth, and the discolorations at the brazed area were observed from the table-plane side. It was found that the discoloration at the brazed area is suppressed with the decrease of ruby erosion at the brazed surface.

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It is necessary to develop excellent sensors in order to improve the automation or the artificial intelligence of the welding operation.
Laser visual sensors are designed to recognize the configuration or debect the position of a weld by irradiating a slit light on to the weld joint, receiving the light with a CCD camera, and then converting the two dimensional information into three dimensional information by using image processing.
The visual sensors for the welding robot must be free from the influence of welding process disturbances, such as light, heat, spatter and fumes.
This paper deals with optical component arrangements and image processing algorithms. The optical component of a sensor head helps to avoid optical window contamination caused by spatters or fumes. The image processor can process image data very quickly and accurately, even if the welding arc light illuminates the surface of the workpiece. The accuracy of detecting the position is within ±0.2 mm.

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The phase transformation at Ta/Zr interface in the diffusion or explosive bonded joint was clarified by employing Zr-Ta binary alloys which were synthesized the bonding interface region between Ta and Zr. Zr-10 mass%Ta and Zr-20 mass%Ta binary alloys were used for the hardness test and microstructural analyses after Formastor-testing and laser surface melting. The cooling rates of Zr-Ta alloys were varied from 0.1 (furnace cooling) to 5.3×10⁵ K/s (laser treating). TEM observation and X-ray diffraction analyses revealed that Ta and α-Zr were identified at the cooling rates up to about 10 K/s, and that ω-Zr as well as Ta was precipitated at the cooling rates between about 100 and 10⁴ K/s. The rapidly cooled alloys (cooling rate exceeded about 10⁵ K/s) were transformed to the single phase of α'-(Zr, Ta) supersaturation solid solution (martensite). The hardness of Zr-Ta alloys indicated the highest value on the condition that both Ta and ω-Zr were precipitated. It could be concluded that the severe embrittlement at Ta/Zr explosive bonded interface was due to the precipitation of Ta and w-Zr attended with the phase transformation in Zr-Ta system.

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Since both electron beam welding and laser welding have higher energy density than GTA and GMA welding, higher speed welding is possible in these welding methods. The cooling rates estimated by the dendrite arm spacings are from 500 to 800°C/s in the welding conditions used in electron beam welding, and from 300 to 1500°C/s in laser welding. According to the result of EPMA line analysis, magnesium segregates near boundaries of dendrites and the maximum content tends to decrease from about 14 mass% to 10 mass% as cooling rate increases, while the minimum content at the dendrite cores has the reverse tendency. The dissolved amount of magnesium in the weld metal is estimated using the relation between lattice parameter and magnesium content by X-ray diffraction technique. In laser welding, the dissolved amounts estimated are less by about 0.3 to 0.5 mass% than that of the base metal and tend to increase as the cooling rate increases. This phenomenon is due to the distribution of magnesium in the dendrites, because the dissolved amount becomes almost the same as the base metal when homogenizing heat treatment is performed on the weld metal. Metallurgical characteristics of aluminum alloy weld metal made by laser are almost the same as those by electron beam, because the cooling rate in the weld metal is almost the same.

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Effects of nitrogen on microstructure and phase transformation temperatures were investigated for near-equiatomic Ti-Ni shape memory alloys arc-melted in Ar-N₂ atmospheres. The nitrogen content in the arc-melted specimens increased with increasing melting time and rising nitrogen partial pressure in atmosphere (arc current 150A, arc voltage 12V, specimen weight 12 g and melting time 0-480 s). With increasing nitrogen content, the amount of second phase observed in arc-melted specimen increased. The second phase was identified as TiN by an electron probe microanalysis and an X-ray diffraction analysis. Both Ms and Af temperatures decreased with increasing nitrogen content of arc-melted specimen. The temperatures of Ms and Af were described by functions of nickel and nitrogen contents.

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At present, the parameters to control the welding deformation of the basic welding joints have been made almost clear and, to some extent, they can be estimated from the welding conditions. However, the welding deformation is expected to depend on welding operators because it is affected by the welding conditions such as welding heat input, leg length, and the restraint of weld joint. Therefore, it is desirable to treat the weld deformations statistically. In this report, as a result of the semiautomatic MAG welding experiment by welding operators having the specified welding skills, the following have been obtained for the angular distortion and transverse shrinkage of the fillet welding tee joint flanges;
(1) The distribution characteristics of the welding heat input and actual leg length when the desired leg length is specified have been made clear.
(2) The distribution characteristics of the angular distortion and transverse shrinkage when the target length is specified have been made clear.
(3) The distribution characteristics of the angular distortion and transverse shrinkage to the welding heat input have come to be presumed from the welding conditions.

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Load carrying fillet welded cruciform joints have two fatigue crack initiating points. They are weld toes and weld roots at which high stress concentrations occur. Which of the two is to be the initiating point depends on weld size, plate thickness and weld penetration, and this mechanism can be easily understood. Some experimental results indicated that fatigue crack originating point was also influenced by the magnitude of stress range. The reason for this phenomenon, however, is not clear yet. In this study, in order to make clear the reason, fatigue tests on the welded joint specimens, analyses of welding residual stresses with the aid of the thermo-elastic-plastic finite element method and fatigue crack propagation analyses in considera-tion of the residual stresses are carried out.

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Generation of residual stresses in high velocity oxy-fuel (HVOF) thermal sprayed coatings was studied by measuring the curvature change of substrates in-situ during spraying. 316L stainless steel, Hastelloy C, and WC-12%Co powders were sprayed by a HVOF gun powered by the combustion of kerosene and oxygen. It was found that the substrate curvature changed through 3 stages : 1) abrupt change at the onset of spraying, 2) continuous change during spraying, and 3) continuous smooth change during cooling after spraying. They correspond to 1) generation of stress within the surface layer of the substrate, 2) within the coating, and 3) superposition of macroscopic thermal stress. The stress during spraying was compressive and could be as much as 400 MPa, depending on the powder material and spray conditions. SEM observation of splats collected on polished substrates revealed that the majority of HVOF particles were not fully molten before impact. Therefore, HVOF sprayed coatings consisted of much thicker and plastically deformed particles than plasma sprayed coatings. The microhardness of the surface layer of the substrates beneath the HVOF coatings was found to be increased significantly whereas no such change was observed for plasma sprayed coatings. These results indicate that the plastic deformation caused by impingement of poorly molten particles at high velocity is the cause of compressive stress during HVOF thermal spraying.

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In this study, fatigue strength improvement methods of weld joints, such as TIG-dressing, hammer peening and burrgrinding are discussed with T-form fillet welded joint specimens. Concerning the crack initiation life, crack propagation life, and improvement mechanism of fatigue strength, fatigue testing, FEM analysis, measuring residual stresses, observation of crack surface and fracture mechanics approach are carried out.
As a result of fatigue testiness, fatigue strengths of all types of improved speciments, especially burr-grinded specimens are higher than as-welded specimens. Effect of decreasing stress concentration by developing the configuration of welded toe is found only at 1 mm thick from treated surface, so that fatigue strength improvement effect of TIG-dressing and burr-grinding is observed only during fatigue crack length is small (N_c). On the other hand, by hammer peening high compressive residual stresses are induced about at 4 mm thick from treated surface so that improvement effect is obtained during crack propagation life (N_p). However, hammer peening induces ditch which is about from 0.2 to 0.4 mm deep from the surface and the ditch work as source of stress concentration like under-cut, improvement effect of hammer peening is not found during crack is small (N_c).

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In elastic dissimilar materials joint subjected to cooling or heating, thermal stresses at the intersection of the edges and the interface are singular. The thermal stresses are represented by the sum of the singular solutions, the no singular solutions and the particular solutions. In this paper, relationship between two stress intensities (K₁ and K₂) for the singular solutions and wedge angles of materials is theoretically investigated for the metal/ceramics composite. The bonded wedge angle, at which the intensities become zero, is shown. The distribution patterns of K₁ and K₂ around the interface edge correspond to mode I and II, respectively. The sign of distribution varies against combination of the wedge angles. The bonded wedge angle yielding K₁ (or K₂) =0 and the conditions for disappearance of stress singularity based on both the stress exponents and intensities are shown on the φ₁+φ₂ (total angle of bonded wedge)-φ₁(wedge angle of material 1) plane. From this plane, combinations of the wedge angles, at which compressive thermal stress is induced around the interface edge, can be found. In addition, thermal stresses around the interface edge in case of finite bodies are analyzed using FEM.

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Very low cycle fatigue strength of welded joints of HT570 steel with weld defects was investigated to study the acceptable size of weld defects in girth welds of gas pipelines under cyclic displacement of land by earthquake. Butt welded joints containing incomplete penetration, porosities, lack of fusion in the intermediate pass, and crack in penetration bead were manufactured and tested under strain controlled conditions.
All specimens tested in this study satisfied the fatigue design curve for girth welds of gas pipelines. The fatigue strength of specimens with weld defects generally decreases with the increase of equivalent defect size. The shape of cracks initiated from defects is affected by the reinforcement, and the surface crack propagates rapidly along the weld toe of the penetration welds and passes through the width of the specimen. The relationship between the J-integral range and the crack propagation rate under very low cycle fatigue load is almost the same as the extension of the relationship in low J-integral range. The crack propagation analysis which regards defects as cracks leads to the relationship between the size of defects and the number of cycles passing through the thickness. The critical size of defects in welds of gas pipeline under cyclic displacement is proposed by the analysis. The critical crack size of the surface defect could be applicable to the buried defect because the surface defects give a more conservative evaluation than buried defects. The analytical results give conservative estimations compared to experimental results.

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The influence of ambient gas on ultrasonic bondability was investigated, in order to obtain a reliable micro-bond with high strength and small deformation when bonding is done at low temperature and low energy conditions. Au, Cu and Al physical vapor deposition films on Si wafers, which are materials with different oxidizing characteristics and different hardnesses, were selected for bonding pads. First the bonding surfaces of the Au, Cu and Al films were treated for contamination by cleaning, and then an Au wire was ultrasonic ball bonded onto each surface in various ambient gases. The surfaces were quantitatively analyzed with Auger electron spectroscopy. After that, the fracture mode of the Au ball bond in a pull test was investigated and ultrasonic bondability was evaluated from a relationship between the successful bonding rate and ultrasonic power. The results are summarised as follows.
(1) The ultrasonic ball bondability in Ar gas containing 0.1 vol% H₂O or 0.2 vol% acetone for an Au wire bonded onto an Au or Al film cleaned by ion bombardment deteriorates in comparison with that bonded in a vacuum. However, in N₂ gas or Ar gas containing 1 vol% O₂ being the same bondability is obtained as in a vacuum. This is attributed to a vapor of H2O or acetone being adsorbed on the metal film surface which acts as a lubricant during ultrasonic bonding of the Au ball to these films and prevents formation of a fresh and cleaned surface of the bonded metal. For the physisorbed gas of N₂, Ar or O₂ this does not occur.
(2) The ultrasonic ball bondability on an Au film is improved by cleaning the film surface and eliminating H₂O and organic vapor in ambient gas until the H₂O content in ambient gas is less than 0.1 vol%.
(3) The ultrasonic ball bondability on an Al film is improved by eliminating H₂O and organic vapor in bonding ambient gas even without special surface cleaning.
(4) The ultrasonic ball bondability of an Au wire onto a Cu film deteriorates in Ar gas containing H₂O, acetone or O₂. In particular for O₂ containing gas, enough bondability to get a 100% successful bonding rate is not obtained within an ultrasonic power of 1000 mW. This is O₂ gas forms an oxide film on the Cu film which is much harder than the Au ball.

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