This paper is concerned with a theoretical analysis of the structure of a transferred arcjet. Integral methods are used to analyze the basic magnetohydrodynamic (MHD) equations for a steady axisymmetric transferred arcjet. By introducing the loss area concept, the basic equations are converted into simple algebraical equations that describe the loss area functions in terms of the plasma properties and operating conditions of the plasma torch. These loss area functions (Displacement Area, Momentum Loss Area, Energy Loss Area) are expected to be useful in gaining a better understanding of the structure of the transferred arcjet and in predicting the cutting perfomance of the transferred arcjet when used for precision plasma cutting of ferrous and nonferrous metals.

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Qualitative analysis to high temperature tensile strength, creep strength and creep ductility of type 308 stainless steel weld metal was performed by using obtained available experimental data. As a result, the effects of interstitial solid solution elements, substitutional solid solution elements, carbide precipitation hardening elements, welding heat input and plate thickness on these properties were made clear.
From the result of qualitative analysis, the formulas of tensile strength and creep strength at 550°C for type 308 stainless steel weld metal were established by multiple regression analysis.
Finally, two types of weld metal, 0.06 mass%C-0.02 mass%N-0.7 mass%Mo and 0.02 mass%C-0.08 mass%N-3 ferrite number, were proposed as the most suitable type 308 stainless steel weld metal for fast breeder reactor by considering the results of qualitative analysis, multiple regression analysis and microstructure observation.

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This paper reports the effect of neutron irradiation on strength of high manganese steel which is a candidate for nuclear fusion reactor components. Cryogenic temperature strengths of two kinds of high manganese steel, A-T (18Mn-6.8Cr-4.7Si) and B-T (22Mn-6.4Cr-4.4Si-0.18N), and their electron beam welded joints were investigated under various irradiated conditions.
Results obtained are summarized as follows.
(1) At cryogenic temperature, high manganese steel A-T exhibited a faint serration, B-T showed a clear serration.
(2) Ultimate tensile strength and 0.2% proof stress of base metal and electron beam welded joint of A-T and B-T increased with increasing of neutron fluence.
(3) Elongation of base metal and electron beam welded joint of A-T and B-T decreased with increasing of neutron fluence.

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Tensile and shearing tests were carried out on four kinds of explosively clad steels in order to examine these strength and ductility at various test temperatures. Four kinds of explosively clad steels are C1100/SUS304, SUS304/SM41B, SUS316/SM41B and TP28/SM41B.
Results obtained are as follows.
(1) Strength of the explosively clad steel, C1100/SUS304, at 700 K is obviously small compared to strength at 293 K. It has excellent strength and ductility at 4.2 K.
(2) Strength and ductility of the explosively clad steels, SUS304/SM41B and SUS316/SM41B at 700 K are sufficient. When the temperature becomes to 4.2 K, these strength is reduced and ductility decreases rapidly.
(3) The explosively clad steel, TP28/SM41B, has a high tensile strength at 700 K or 4.2 K and has a low shearing strength at same temperature.

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This study has been carried out to explain the effect of sintering temperature on life time of cathode for air plasma cutting.
Zr-Y₂O₃, Hf-Y₂O₃ and Ru-Y₂O₃ systems were studied and compared. It was concluded that; in the cases of Zr-Y₂O₃ and Hf-Y₂O₃ electrodes, the sintering temperature was a little effect on the electrode consumption. Also, the erosion resistance during discharge was not improved by adding Y₂O₃.
On the other hand, in Ru-Y₂O₃ electrode, the erosion resistance during discharge was remarkably improved by adding Y₂O₃. Its different property is related to the high density of sintered body which is sintered at comparatively high temperature, 2373 K.

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This paper describes physical properties of sintered Ru-Y₂O₃ system for cathode material in oxidizing atmosphere ; thermal properties (thermal diffusivity, specific heat and thermal conductivity) and electrical resistivity. And explain the relationship between its physical properties and electrode consumption.
The thermal properties are measured by laser flash method and the electrical resistivity are measured by four terminal method at room temperature.
80Ru-20Y₂O₃ electrode which has superior erosion resistance showed high thermal and electric conductivity comparing with those of Zr and Hf.

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The purpose of this study is to investigate the effect of twist angle on tensile strength of diffusionwelded joints by using molybdenum single crystals with (121) and (025) surfaces. Relation between the twist angle and strength is tried to explain with the coincidence site lattice model and a theoretical model calculation. The results are as follows:
Single crystals could be welded without recrystallization. Tensile strength of the joints depended on the twist angles. The joints with twist angles up to 10 degree were as strong as the base metal. In case of the twist angles above 10 degree, there were peaks in tensile strength of the joints around the certain twist angles where a number of common lattice points were formed at welding interface. From the calculation, it was shown that the binding energy between the crystals decreased with decreasing the number of common lattice points. Twist angle widths of peaks in tensile strength were estimated with the Brandon's equation.

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The demixing in gas tungsten arc plasma was investigated by measuring of the helium concentra-tion at a water-cooled copper anode using a mass spectrometer in argon-helium mixed gas shielding arc. It was expected from a study on arc pressure that helium gas, which is lighter than argon gas, is efficiently absorbed near the electrode tip by the plasma stream.
In this measurement, a small amount of plasma gas was sampled through a hole (ID: 0.5 mm) in the anode plate by using a setup similar to that of a leak test for a vacuum chamber using mass spectrometer. The helium concentration of the gas was determined from a ratio of the helium spectrum peak value to that of argon in argon-helium arc.
From measured concentration distribution of helium at the anode, it was found that helium concentrated in the arc center at the anode surface and it was suggested that argon concentrated at the arc periphery in argon-helium arc.
Furthermore, it was shown that blow holes were formed in argon-helium arcs upon introduction of nitrogen. Blow hole formation occurred at lower nitrogen content when argon content in the shielding gas was high. These results could be understood from mass spectroscopic measurements which showed that helium gas concentrated at the core in helium-nitrogen arcs as well as in argon-helium arcs, but both nitrogen and argon distributed uniformly throughout the arc in argon-nitrogen arcs.

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This paper describes the use of high-C welding materials for rail welding, which provide rail weld metal with improved wear resistance. The high-C weld metal prevents liquation cracking at rail HAZ caused by the significant difference in the melting points between weld metal and HAZ when using conventional low carbon low alloy electrodes.
Fundamental studies have been made on how to manufacture electrodes with carbon up to 1% and how to avoid solidification cracking likely to occur in high carbon weld metal.
The results of this study are as follows :
1) The high-C electrodes have been successfully manufactured
2) The microstructure of high-C weld metal is of fine lamellar pearlite which is known to be highly wear-resistant.
3) The liquation cracking at HAZ can be avoided by the use of weld metal with carbon higher than 0.4%.
4) The occurrence of weld metal solidification cracking is facilitated in high-C weld metal. This cracking can be prevented by a control of molten pool configuration through appropriate manipulation of electrodes.

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This paper describes the use of high-C welding materials for enclosed-arc welding of high strength rail. Experiments have been done to improve the facility of manipulation of the high-C electrodes to find the optimum welding procedures and to find weld joint performances of high-C welds.
The experimental results are as follows :
1) It is necessary to keep the flux weight ratio to core electrode between 22 and 23%, the ratio of CaO/ CaF₂ in flux around 1.6, and carbon content in weld metal less than 0.5% so that welders can preferably manipulate electrodes to remove molten slag swiftly out of molten weld pool.
2) The welding conditions and the pass sequences specific to the high-C welding have been found so that sound welds free from solidification cracks in weld metal and liquation cracks in HAZ can be obtained.

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To prevent weld defects likely to occur in DC-MIG welding and to avoid arc-instability due to elec tromagnetic blow in DC-MIG welding, an AC-MIG welding has been developed which uses high voltage pulse from a pulse generator sympathized with industrial frequency.
This process enables to avoid the weld-defects caused by lower arc pressure exerting on the molten pool. Furthermore, this process can provide weld metal of a low oxygen content with high toughness.

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A pulse generator with a L-C-R circuit sympathized with the industrial frequency has been developed to facilitate the arc re-ignition in the high-current AC-MIG welding process.
Weld-defects can be avoided in this process because of lower arc pressure exerting on molten pools than in conventional DC-MIG. Furthermore, this process provides low oxygen weld metal with high toughness. Further improvement had been desired in the reliability of a Pulse Generator in order that this process can be used in practice.
It has been clarified that the most important parts in the pulse generator is thyristors as switches in the L-C-R circuit which need a considerable allowance against high pulse current and voltage.

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The Ni-Ti type shape memory alloy has been applied in many fields, though the welding process for it is not so sufficiently studied. The development of various welding processes must bring this alloy to the wider use in more fields.
So far, the study on the electron beam welding, the laser welding, the resistance welding and the friction welding of this alloy has been reported. However, few studies on the brazing would be found.
This paper describes the brazing of Ni-Ti type shape memory alloy using Ag-based filler metals.
A newly developed flux consisting of AgCl-KF-LiCI succeeded in wetting this alloy surface by the Ag-based filler metal. The addition of approximately 2 mass % Ni in an Ag-based filler metal showed the considerable increase in tensile shear strength of the brazed joint compared with a conventional Ag-based one.

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A5083/SUS304 is known as a very difficult combination to weld by an explosive welding technique. This combination is tried to be explosively welded using thin SUS304 intermediate plate. The formation of thick interfacial zone at welded interface disturbs the bonding between the interface and the microstructure of this interfacial zone is composed of Al and Fe₄Al₁₃. Separation is generated at SUS304/interfacial zone or inside the interfacial zone. The position of the separation fabricated by explosive welding is different with it fabricated by the other method which uses heat treatment. Since the thick interfacial zone is formed by excess energy at the interface, to insert thin SUS304 plate is effective as to decrease the energy dissipated by the collision between plates. Moderate collision velocity is also required for good bonding to generate the metal jet. Welding window is constructed by the parameters of kinetic energy loss by collision (ΔKE) and collision velocity (V_p), and the weldable range of this combination is V_p =350-670m/s and ΔKE=1×10⁵-5.5×10⁵J/m².

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Behavior of TIG arc spot welds of Al alloy A5083 thin plate during cooling and solidification process was investigated by the following methods.
Temperature of welds was measured during heating and cooling process by using very slender thermocouples. Weld specimen was broken at any time during cooling and solidification process by using a high speed breaking apparatus.
Afterwards, morphological macro- and micro-structures of fracture surface were observed using electron microscope.
The results obtained are as follows:
1) There developed a liquefied grain boundary, which is called a brittle zone, and a partial liquefied grain boundary, which is called low ductility zone, in HAZ when some time passed after arc stop.
2) Solidification end was determined by confirming disappearance of liquid phase on fracture surface. As a result, it was found that the temperature of solidification end of weld metal was considerably lower (440-425°C) than solidus temperature (579°C) of base metal.
3) CCSP diagram was obtained from fractography analysis by determining solidification end, which was difficult to determine from analysis of cooling and solidification curve.

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The mechanism of the grain refining observed in the zirconium containing ferritic stainless steel overlay weld metal has been investigated.
The grain size in the overlay weld metal manufactured with the filler metal containing chromium ranging from 19% to 30% with no addition of zirconium was almost same regardless of the chromium content.
The grain refining in the overlay weld was remarkably promoted by the increase of the zirconium content in 19Cr-2Mo steel filler metal.
Most intergranular and intragranular zirconium carbide in the overlay weld metal precipitated during cooling in welding thermal cycle. Increasing in zirconium content provided the increase of intergranular carbides and made the grain boundary jigzag manner, which suggested that the zirconium carbides act as the obstacle against the grain boundary migration.
On the basis of these results, it was suggested that the precipitation of intergranular zirconium carbide was a main factor of the grain refining.
The theoretical model has made clear that the grain refining in the overlay weld by the addition of zirconium was attributed to the retardation of grain growth during the weld thermal cycle, which was caused by pinning effect of zirconium carbide against the grain boundary movement.

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Effect of aging treatment on hardening characteristics in HAZ of Ti-15V-3Cr-3Sn-3Al titanium alloy was investigated by means of transmission electron microscopy and X-ray diffraction technique.
As the aged Ti-15V-3Cr-3Sn-3Al alloy was welded by using DCRP-TIG welding procedure, the decrease of the hardness occurred in the heat-affected zone, because of the solution of α phase. The hardness in the HAZ was considerably higher than that of the base metal, as the welded sample was aged at 773 K after welding.
Maximum hardness after aging treatment increased with increasing solution treatment temperature. The precipitation of α phase occurred, as the specimens were aged at 573, 673, 773 K after solution treatment. The precipitation amount of α phase increased with increasing solution temperature at any aging temperature.
The high solution treatment temperature also caused homogeneous precipitation and fine precipitation of α phase during aging by means of transmission electron microscopy.
Consequently, the high hardness was due to the fine precipitation of α phase.

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Laser speckles can be used to measure surface strains without contact because they deform with a specific relation to the deformation of the surface illuminated by a laser beam. If it can be applied to the measurement of dynamic strains at high temperature as encountered in welding processes, it is hoped to help clarify various problems such as high-temperauture cracking. However, several problems such as disturbances due to the intense emission from the welding arc, oxidation of measuring surface, and fluctuation of the surrounding atmosphere due to convection must be overcome.
In this study, several preliminary experiments were carried out in order to examine the applicability of the laser speckle method to welding:
1) Effects of several measurement parameters on the accuracy of the strain measurement.
2) Measurement of dynamic strains on the rear surface in TIG welding of stainless and mild steel.
It was found that a larger laser spot on the measuring surface gives better accuracy and stability in the measurement for the cost of spatial resolution. In the dynamic measurement, it was difficult to obtain reliable strain values when the strain rate was higher than 1×10^-3/sec. With strain rates below this value, reasonable agreements were obtained between the strain values measured by the laser speckle method and those by strain gauges. In the welding process, such a high strain rate occurs during the period right after the ignition of arc or when the arc is passing over the measuring point. It is concluded that it is necessary to speed up the sampling rate of the current speckle recording apparatus in order to widen the applicability of the method. Since some other noise factors such as out-of-plane displacement are also most vigorous during such periods, it will become necessary to take those factors into account too.

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The adhesion of plasma sprayed coating to substrate was inspected by ultrasonic testing method. As the probe, an immersion-type probe was used. Sprayed coatings were obtained by spraying NiCr alloy powder to SS41 mild steel plates by plasma jet spraying process.
Main results obtained are summarized as follows:
1) The adhesion of sprayed coating to substrate can be inspected by ultrasonic testing method, especially by detecting bottom echo, B_c.
2) Bottom echo increases with increasing adhesion strength of coating to substrate.
3) Some image displaying methods by computer graphics, by which location and shape of peeling of coating and adhesion distribution are able to be visualized, were constructed.
4) Some parameters to evaluate the adhesion of coating (S_eff/S₀, B_cav/B_b, B_cmax/B_b) were proposed. Although some correlations between these ultrasonic parameters and adhesion are recognized, they had relatively large dispersion.

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At cutting speed faster than 3 m/min surface roughness of kerf of thin steel plates cut with CW CO₂ laser (having power ripple) has a close relation to the fluctuation in intensity distribution at focal point.
Measurements were made to determine intensity distribution of focused laser beam and laser power ripple in terms of amplitude and frequency. The kerf width was found to be approximately equal to a critical beam diameter, at which power density correspond to 1-1.5×10⁵ W/cm², and is 1/30 to 1/40 of peak value of beam profile. A thermal conduction model was proposed to predict the surface roughness, in which the surface roughness is equal to the amplitude of change in the critical radius up to frequency of 1 kHz, and decreases at frequencies higher than 1 kHz. It was found that the surface roughness can be predicted by this model, when the intensity profile of the focused laser beam and laser power ripple are given.

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The thermal distribution of the bond including electrode tips during bonding process is shown experimentally and the role of bonding parameters such as electrode force, input power, and current duration is clarified in micro parallel gap bonding processes. Furthermore the formation of the bond is investigated experimentally at the bonding of copper alloy lead and thick film (Ag/Pd) with 20μm thickness on the 96% alumina substrate.
To obtain the bonds with high quality, it is very important to control both the thermal distribution of the bond and its stability.
Resulting from the each voltage value of bonding parts, it is clarified that heat generation mainly occurs at the part between electrode tips and copper alloy lead by joule's heating and the current mostly flows into Cu alloy lead through the electrode tip, and so the current from copper lead to thick film is very small. As the result, temperature rise of the bond is caused by heat conduction from the part at the interface of the eletrode tip and copper lead.
Tensile shear load of the bond is influenced by power input, current duration under constant electrode force. Maximum load of the bond can be obtained with a shorter current duration by increase of the power input and the substrate is fractured by thermal shock, but expulsion occurs at the interface of the electrode tips and copper lead by increasing with the current duration.

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The temperature and behaviour of Sn, Ag, and Cu at the interface of the bond are shown experimentally at bonding of the copper lead and Ag/Pd thick film on the 96% alumina substrate in the micro parallel gap bonding processes.
The temperature at the interface of the bond can be measured by measuring thermal electromotive force between the copper lead and thick film using probes at the instant of the bonding current reaching zero after switching off.
Increasing input power and current duration, the interface temperature at the bond is increased from 420 k to 830 k, and furthermore, its temperature increases rapidly with current duration and becomes more unstable with increasing power input.
The interface temperature increases with current duration under bonding condition of 300-500 W, 1-4.99 ms, and 23.3 N. Sn can diffuse very rapidly into Cu lead and thick film in the case of interface temperature being above melting point of tin. At same time, Ag and Cu are diffused to tin liquids, and so the intermetallic layers of Ag-Sn-Cu near the interface of the bond are formed. Furthermore it is observed that the fillet of Sn is made at edge of bond.

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