The interfacial microstructures of two typical contact films for gallium nitride (GaN) have been investigated by transmission electron microscopy. One is a 300-nm-thick Ni single-layer deposited on p-type GaN and then annealed at 873 K. Ni₅Ga₃ is formed at the interface by the post-deposition anneal. As the other product of the interfacial reaction, N₂ voids are formed bulging to the Ni-side. The other contact film consists of four layers: Ti, Al, Ni, and Au, at the initial state. By annealing at 873 K for 300 s, the reactions proceed between GaN and Ti and also among the layers. The reaction at the GaN/Ti interface forms a thin layer of TiN adjacent to GaN. The layered structure disappears completely due to the interlayer reaction and subsequent growth of the reaction product grains.

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To confirm the effectiveness of Co and Ni addition to Sn-Ag system lead-free solder on reduction of erosion of iron plating of soldering iron tip, Sn-Ag-Cu-Co(-Ni) system flux cored solder wires were used in operation lines under several manufacturing operation conditions. The temperatures of soldering iron were maintained at about 623–663K. The degree of damage was evaluated by cross sectional measurement of the thickness of Fe plating before and after soldering operation. The obtained data had relatively large scattering, but the Co and Ni addition was found to be effective to suppress erosion damage in all operation lines. Double addition of Co and Ni was also confirmed more effective than single addition of Co.

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The severe erosion damage, which is caused by a molten lead-free solder, of wave solder equipment made into stainless steel has been encountered in operation. Then, the higher maintenance frequency and reduced life time of wave solder machine component is a serious issue in a manufacturing process. In this study, the evaluation method of erosion of stainless steel by molten lead-free solders was investigated using micro-focus X-ray systems for fluoroscopic and computed tomography (CT). As a result, it was found that the fluoroscopic image could truly reconstruct the cross-section shape of the stainless steel sample after immersion test without destruction. In the case of X-ray systems for fluoroscopic and CT used in this study, three-dimensional data can be obtained. Therefore, it was possible to easily check the whole picture of the test sample after immersion test and to decide the maximum erosion depth of test sample.

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The investigation of welding induced distortion requires knowledge regarding the heat effects of welding in terms of a precise description of the temperature field. Welding simulation enables to understand basic phenomenological mechanisms and to evaluate different welding configurations which is, in contrast to experimental investigations, more time- and cost-efficient. The complex physical phenomena of welding processes demand the calibration of phenomenological models against experimental reference data. The calculation of a temperature field that approximates the experimental one very accurately is still a time consuming and difficult task. This is caused by the fact that the model input which yields the optimal temperature field cannot be derived from parameters of the real process directly. This paper focuses on a recently introduced approach that combines empirical and phenomenological modeling techniques. The calibration of the weld thermal models is performed automatically by means of a global optimization scheme and does not require the definition of initial model input parameters. This key feature confirms the benefit potential when it comes to practical utilization of welding simulation because the calibrated temperature field is provided within few minutes without the need for expert knowledge. This is the basis for an efficient determination of the welding induced distortions for industrial applications. Furthermore, the representation of the relationship between model input parameters and process parameters by a neural network enables to predict the temperature field for unknown process parameters that were not considered for calibration. Consequently, the combination of phenomenological and empirical models permits to reduce the experimental effort and bridges the gap between numerical and experimental investigations of the heat effects of welding. The application of this modeling approach is independent of the welding technique under investigation. Exemplarily it is tested for laser beam and GMA-laser hybrid welding. All numerical calculations are validated experimentally.

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To form curved surface, in-plane strain is induced into a plate by line heating, press working or laser heating in shipbuilding or sheet metal working. Laser forming could be a potential useful method by which press working could be replaced. It is thought to be useful to know distribution of in-plane strain added into the thin plate during forming curved surface, so that workers can show a place and amount of additional in-plane strain in their next step. The process to measure in-plane strain in an actual curved surface seems still not to be reported. In this report, in-plane strain distributions existing in bowl shape thin plate made by laser heating is investigated with geodesic lines drawn numerically on the surface. The in-plane strain is calculated from distance change of two geodesic lines. This in-plane strain distribution agrees with a strain distribution measured from shrinkage of the plate when the plate length is long. When plate length is short, these strains do not agree with each other. In this case, existence of some elongations cancelling effective in-plane strains appears as width change of the plate. As a result, in-plane strain measured by geodesic lines is useful to indicate performance of curved surface forming process.

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In order to investigate the effect of welding conditions on reduction of angular distortion by in-process control welding using back heating source, numerical analysis is done. Furthermore, positional condition setting of back heating source and required back heat input for complete control of residual angular distortion are discussed. These results show that in-process control welding by back heating immediately behind of welding torch can be extremely effective to reduce angular distortion.

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The effect of transformation expansion on the restraint stress was investigated by numerical simulation. A RRC-type weld joint with y-slit groove were used for the calculation of restraint stress. The transformation temperature Ms of weld metal and the restraint intensity R_F of the joint were varied systematically. The lower the transformation start temperature M_s is, the lower the restraint stress σ_w at room temperature becomes. The higher the restraint intensity R_F is, the lower the restraint stress σ_w at room temperature becomes.

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This paper reports measured and estimated results of residual stress distributions of butt-welded austenitic stainless steel pipe in order to improve estimation accuracy of welding residual stress. Neutron diffraction and strain gauge method were employed for the measurement of the welding residual stress and its detailed distributions on inner and outer surface of the pipe as well as the distributions within the pipe wall were obtained. Finite element method was employed for the estimation. Transient and residual stresses in 3D butt-welded joint model were computed by employing Iterative Substructure Method and also commercial FEM code ABAQUS for a reference. The measured and estimated distributions presented typical characteristic of straight butt-welded pipe which had decreasing trend along the axial direction and bending type distributions through wall of the pipe. Both results were compared and the accuracy of measurement and estimation was discussed.

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Numerical simulations by thermal-elastic-plastic-creep analysis using finite element method (FEM) have been performed to evaluate residual stress distributions in a reactor pressure vessel (RPV) caused by weld-overlay cladding, post-weld heat treatment (PWHT), hydrostatic test, operation and pressurized thermal shock (PTS). The weld-overlay cladding gives tensile stress in the cladding layer and base metal near the cladding. Using the calculated welding residual stress, stress intensity factors (SIFs) during PTS have been computed based on the influence function method. The maximum value of SIF during PTS with weld-overlay cladding is higher than that without weld-overlay cladding. According to the structural integrity assessment procedure of an RPV against PTS, a comparison has been also made by defining a temperature margin. The result indicates that the residual stress makes the temperature margin smaller in a few degree C which may be within the range of the margin originally put in the structural integrity assessment procedure.

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Mechanized or Automated Ultrasonic Testing of pipeline girth welds is now in common use in the on - and offshore industry. Automated ultrasonic testing (AUT) is globally seen as more than just an alternative to the standard radiographic inspection technique not only because it does not poses safety hazards but also because it is faster, more reliable and has better detection capabilities of critical Lack of Fusion defects in pipeline girth welds. One of the reasons to use the AUT technique is due to its possibility to use acceptance criteria which are based upon ECA (Engineering Critical Assessment) instead of the so-called "Good Workmanship". Usually the AUT systems are mounted on a band strapped around the pipe. From the weld, ultrasonic data is collected from which the defect sizes and positions can be determined by experienced operators using dedicated software algorithms. This paper discusses the RTD Rotoscan system, which is the first worldwide AUT inspection system for new construction pipeline girth welds. The principles of AUT, the conventional RTD Rotoscan as well as the RTD phased array Rotoscan and its advantages in comparison with conventional (multi probe) AUT are discussed. Furthermore challenges regarding the use of AUT on Austenitic welding having a corrosion-resistant alloy layer are presented. This paper describes also latest improvements made on AUT during the last years in order to optimize inspection philosophy and minimize the system's "Uncertainties". In addition a brand new method, RTD IWEX, is briefly described that allows the detection and sizing of weld imperfections in 3D.

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