Recently, the use of environment-friendly manufacturing technology has increased in the electronics industry worldwide. In particular, the replacement of lead-containing solder with lead-free solder has been widely investigated. In this paper, laser welding of Cu wires bundle and dumet wire for the production of thermistors has been investigated as an alternative to soldering. The results are summarized below. When laser irradiation was applied to the end of the Cu wires bundle, the molten portion shrank and solidified in the direction of the laser irradiation. Laser welding without failure was achievable when the laser irradiation was applied at right angles to the lap direction of the Cu wires bundle and the dumet wire, and the laser irradiation position was shifted towards the dumet wire from the axis of the Cu wires bundle. The ends of the wires could be incorporated in the weld. Both the electric resistance and the tensile breaking load of the weld were equivalent to those of the dumet wire. It was possible to achieve perfect laser welding by experimenting with clamping, movement, lapping of wires and laser irradiation with the welding apparatus.
HCA (Hollow Cathode Arc) is expected to be a welding heat source in outer space because HCA is sustainable in vacuum. HCA in vacuum makes huge penetration compared to GTA at atmospheric pressure. Oxide layer on aluminum alloy is removed by HCA. The oxide film is known as obstructor for normal bead formation. The shape of crater by HCA is conical. It is thought that the destruction of aluminum oxide layer and the formation of conical crater are largely-concerned with the evaporation of the base metal. The objective of this study is to develop a HCA welding simulation model. Present model can be applied to aluminum alloy. Evaporation from the metal surface is taken into consideration in the model.
Weldability in neutron-irradiated low alloy steel for reactor (pressure) vessel has been studied by temper-bead repair-welding of low-heat-input TIG and YAG laser welding. A low alloy steel and its weld, and stainless steel clad and nickel (Ni)-based alloy clad were irradiated in a materials test reactor (LVR-15, Czech Republic) up to 1.4 X 1024 n/m2 (>1 MeV) at 290°C, which approximately corresponds to the maximum neutron fluence of 60-year-operation plants' vessels. The He concentration in the irradiated specimens was estimated to be up to 12.9 appm. The repair-welding was carried out by TIG and YAG laser welding at a heat input from 0.06 to 0.86 MJ/m. The mechanical tests of tensile, impact, side bend and hardness were carried out after the repair-welding. Cracks were not observed in the irradiated low alloy steel and its weld by temper-bead repair-welding. Small porosities were formed in the first and second layers of the repair-welds of low alloy steel (base metal). However, only a few porosities were found in the repair-welds of the weld of low alloy steel. From the results of mechanical tests, the repair-welding could be done in the irradiated weld of low alloy steel containing a He concentration up to 12.9 appm, although repair-welding could be done in base metal of low alloy steel containing up to only 1.7 appmHe. On the other hand, cracks occurred in the heat affected zones of stainless steel and Ni-based alloy clads by repair-welding, except by YAG laser repair-welding at a heat input of 0.06 MJ/m in stainless steel clad containing 1.7 appmHe. Based on these results, the determination processes were proposed for optimum parameters of repair-welding of low alloy steel and clad used for reactor (pressure) vessel.
We hold many expectations that aluminum-clad steel will be applied for functional material, structural transition joint for welding steel structure to aluminum structure and so on. In this study we investigated the effects of aluminum purity and/or bonding conditions, which were bonding temperature, reduction rate of aluminum plate thickness (RAl), vacuum degree, on bond tensile strength of aluminum-clad steels produced by the vacuum roll bonding. And also the bond interfaces were observed using a high-resolution transmission electron microscope (RE-TEM). When A1050/SS400 clad materials, which produced at more than 450°C in bonding temperature, more than 17% in RAl and less than 10 Pa in vacuum degree, were performed in tensile test, they fractured through base metal of the aluminum. The values of bond tensile strength were obtained over 100 MPa. The bond tensile strength of 4N-Al (99.99 mass%Al) /SS400 clad material, which produced at 500°C in bonding temperature, 20% in RAl and 3 Pa in vacuum degree, was obtained about 80 MPa and test piece fractured through base metal of the aluminum. In the analysis results for bond interface of A1050/SS400 clad materials (500°C in bonding temperature, 20% in RAl and 3 and 10 Pa in vacuum degree) using a HR-TEM and an electron dispersive spectroscopy (EDS), no intermetallic compound and continuously amorphous phase in thickness from 2 to 3 nm were observed. The composition of the amorphous phase consists of mostly Al, O, Fe and Si. For the bonding interface of 4N-Al/SS400 clad material (500°C in bonding temperature, 20% in RAl and 3 Pa in vacuum degree), amorphous phase and nano-crystal were observed using HR-TEM. Therefore, it was clarified A1050 and 4N-Al/SS400 clad materials obtained using a vacuum roll bonding were bonded through the amorphous phase.
This study evaluated the weld joint performance of X80 line pipes welded using fully automatic Gas Metal Arc Welding and manual Shielded Metal Arc Welding in order to clarify welding conditions for yield stress overmatching with adequate fracture toughness and hardness taking into account the distribution of the yield stress of line pipes. In addition, we conducted metallurgical surveys of the weld metal to clarify factors dominating the yield stress of the weld metal. The results clarified that the welding conditions applicable to X80 line pipes were the heat input range of between 0.9 and 1.3 kJ/mm using solid wires classified as YGW24 and ER100S-G for GMAW and that of between 1.6 and 2.4 kJ/mm using electrode classified as E11016-G for SMAW. The metallurgical surveys revealed that the yield stress of the weld metal was dependent on the acicular ferrite lath width and percentage of the grain boundary ferrite, ferrite side plate and acicular ferrite. The heat input dependency of the yield stress of the weld metal could be explained from the viewpoint of the acicular ferrite lath width which was the main microstructure.
The applicability of built-up repairing by isothermal solidification to Ni-base single crystal superalloy CMSX-4 was investigated using Ni-Cr-B filler metals. Base metal dissolution and isothermal solidification behaviors were examined under various heat treatment conditions. Microstructure of the repaired region could be classified into eutectic zone, normally solidified zone, isothermally solidified zone, precipitated zone in the base metal and substrate. Isothermally solidified zone and precipitated zone in the base metal were found to possess the identical crystal orientation with the base metal one. The dissolution width of base metal and the isothermal solidification width increased with repairing temperature and holding time. The single-crystallization could be achieved in the isothermally solidified zone of the repaired region. The built-up repairing up to 38μm in width could be made at the repairing condition of 1448K×176.4ks by using a Ni-Cr-B filler metal.
This paper deals with the useful estimating method for toughness of welded metal by Laser Beam Welding (LBW). Under present circumstances, LBW is not applied for non-redundant structural member, because of toughness of the welded joint cannot be verified due to Fracture Path Deviation (FPD). In the study, 7 types of carbon steels and their welded joints have been evaluated by Charpy impact test and CTOD test. Many FPD has been observed and it is confirmed that FPD probability is tend to decrease, as the test temperature decreases. Therefore, the estimating method for toughness of LBW welded metal; using data tested in lower temperature has been established. For estimating a proper transition temperature, 3 valid data (at least one of them measured above the temperature as "Energy transient temperature—20 degrees") is required. Using the method, Charpy absorbed energy has been estimated with sufficient precision.
Behavior of displacement at welded joints during welding is an important factor for reliability of the joints. But in-situ measurement of the behavior is very difficult because contact method such as strain gauge is inapplicable in high temperature. In this study, ESPI (Electronic speckle pattern interferometry) system is applied to in-situ measurement of displacement increment distribution in SUS304 steel, 9%Ni steel, and low transformation temperature welding (LTTW) material during GTA welding. Qualitative tendency of measured results agrees with numerical simulation. Expansion behavior of phase-transformation is detected in 9%Ni steel and LTTW material during cooling. Moreover ESPI system enabled measurement of displacement increment at uranami bead surface and surrounding area of molten pool. These results show that ESPI system is applicable to measurement of displacement distribution at welded joints during welding process.
The low-cycle fatigue behavior and the relationship between the surface features in the low-cycle fatigue testing and the fatigue life of Sn-3.5Ag and Sn-0.7Cu lead-free solders were investigated at strain rate of 0.1%/s with a non-contact extensometer at room temperature (22°C), 80°C and 120°C. In addition the fatigue life using the surface deformation of those solders were defined and estimated from the surface features of solders investigated by image processing and compared with Coffin-Manson type of fatigue behavior of solders. The fatigue life of Sn-3.5Ag solder was superior to that of Sn-0.7Cu solder under temperatures of 80°C and 120°C. The fatigue life defined from surface deformation indicated a close behavior to Coffin-Manson type of fatigue behavior in those solders. This method could identify the low-cycle fatigue life of solders from the surface deformation.
We aimed at development of thin film capacitor alternatives to multi-layer ceramic capacitor fabricated by sintering. It is necessary to improvement of dielectric properties of BaTiO3 film up to bulk level. In this study, an artificial dielectric super lattices technique by pulsed laser deposition was performed. Multilayer BaTiO3-SrTiO3 thin films were prepared on Pt(111)/Ti/SiO2/Si(100) or SrTiO3(111) by controlling the arrangement of perovskite structure A-site ion in nano-scale. The lattice of the films in the hetero-epitaxial interface at (111) plane was expanded by compressive strain due to lattice mismatch. Cycle of layer was evaluated from diffraction angle of satellite peak by equation for superlattice structure. Dielectric constant of the multilayer BaTiO3-SrTiO3 thin films enlarged at [BaTiO3(2.5nm)/SrTiO3(2.5nm)]20 was 550, compared to solid solution thin film of 390.
This study investigates the friction welding conditions for sound friction welded joint of high density polyethylene round bar and pipe. A comparison of joining phenomena of round bar and pipe is carried out. The mechanisms of generation of polyethylene dust and its preventive means are examined. The results of this experiment are as follows; 1) The sound friction welded joint of polyethylene round bar was obtained, when friction welding conditions were friction time t1=20s, upset time t2=60s, friction pressure P1=0.10MPa, upset pressure P2=0.10MPa, rotational speed N=60s-1 and t1=25s, t2=60s, P1=0.05MPa, P2=0.05MPa, N=60s-1. These conditions are strict, compared with carbon steel. 2) Tensile strength and elongation of sound friction welded joint of round bar were 25.2-25.4MPa and 749-757%, respectively. These were nearly equal to that of the base polyethylene. 3) In the case of round bar, unbonded area occurred if the friction pressure was more increased than the sound friction welded joint condition. The tensile strength of this joint decreased slightly but the elongation decreased remarkably, compared with the base polyethylene. 4) A good welded joint of polyethylene pipe was obtained, when the friction welding condition of friction time t1=5s, upset time t2=60s friction pressure P1=0.10-0.25MPa, upset pressure P2=0.10-0.25MPa, rotational speed N=60s-1 was given. 5) Tensile strength and elongation of sound welded joint of pipe were 23.4MPa and 520%, respectively. These were nearly equal to those of the base polyethylene. 6) There were two main causes of generating dust in the polyethylene pipe. First, polyethylene became hard in the initial friction welding because heat generation by friction welding was low. Second, polyethylene was shaved by friction pressure and rotation. Consequently, the way of preventing dust generating is to preheat the faying surface at about 393K before friction welding.
The development of TLP-bonding process for Ni-base superalloy, Inconel 718 has been carried out using the Bayesian Expert System for TLP-bonding. In order to skip the homogenising treatment, alloy system for insert metal was selected as Ni-Mo-Cr-Nb-Si-B system. The evaluation factors introduced as an index of bonding performance of an insert metal involved the melting point of insert metal, hardness and formability of brittle phases in the bond layer. The chemical composition of Ni-3.0Mo-6.4Cr-4.7Nb-2.0Si-1.0B (mass%) was determined as the optimal composition of an insert metal. The processing parameters have been optimised with three evaluation factors; the joint strength, reduction of area and toughness. The optimal bonding condition was determined as 1459K×3.3ks. Brittle phases were not formed in the bond layer by using a newly developed insert metal, and the joint strength and toughness was over 80% of the base metal properties.
The pre-heating effect was investigated of friction stir welding of A5052-H34 aluminum alloy. At first, the friction stir welding at room temperature was carried out and the distribution of temperature of specimen surface was measured in welding. Friction stir welding with heating was carried out at 150, 250, 300, 350 and 400°C, selected referred to the distribution of temperature. The joint integrity was evaluated by observation of appearances of welded part and its cross section. Good joint was obtained at temperature up to 300°C. Over 350°C, it seemed that the joint integrity had some defects due to an overplus of heat. On the other hand, the tensile strength of joints by friction stir welding with heating was close to it of non-heating one. Therefore, friction stir welding with heating would be feasible.