Metal transfer modes in GMA welding process are different from welding variables: current, voltage, shielding gas, electrode wire and etc. Essentially they are influenced by physical properties of molten metal and electro-magnetic force. Then we numerically investigated the time-change of liquid transfer process using calculation model developed. The numerical result agreed very well with experimental result of water drop transfer from cylindrical nozzle. Numerical analysis shows that liquid transfer modes depend on the pressure balance at the tip of drop. When the dynamic pressure induced by liquid flow is lower than capillary pressure due to surface tension, globular transfer occurs. In contrast, when the dynamic pressure of liquid flow is higher, spray transfer occurs. In the case that the electrical current flows in the liquid, electro-magnetic force significantly influences on the transfer mode and the drop detachment. As for liquid flow-out from the nozzle of 1.2 mm in diameter, calculated results with use of physical properties of molten mild steel show that electro-magnetic force induced by higher current than 250 A changes the transfer mode from globular to spray. Whereas in real GMAW with pure argon gas shielding the transfer mode changes at around 230 A. The behavior of drop detachment is varied by both spatial distribution and time-change of the electro-magnetic force.
The effect of dilution on microstructure and toughness of dissimilar weld metal of super-austenitic stainless steel using nickel base alloy filler wire was investigated. As the dilution increased, the kind of inclusion was changed from Nb(C,N) to Laves phase and the amount of Laves phase increased because of higher phase stability at dendrite boundaries by solidification segregation. Consequently, the toughness of dissimilar weld metal was lower than that of deposited metal.
The effect of dilution on pitting corrosion resistance of dissimilar weld metal of super-austenitic stainless steel using nickel base alloy filler wire was investigated. As the dilution increased, Cr and Mo concentration at dendrite cores became lower because of solidification segregation and the amount of inclusions at dendrite boundaries increased. Consequently, the pitting corrosion resistance of large diluted dissimilar weld metal was deteriorated.
The FSW of an oxide dispersion strengthened platinum alloy using an Ir-based alloy tool was performed. When the welding temperature during FSW was lower than the annealing temperature, abnormal grain growth was seen in the joint after annealing. On the other hand, the microstructure of the joint after annealing maintained finer grains when the welding temperature was higher than the annealing temperature. When the finer grain was maintained, the hardness of the joint after annealing was the same as before annealing and the tensile specimens fractured at the base metal part at room temperature. However, the tensile specimens fractured at stir zone with a large deformation during the high temperature tensile test at 1500°C.
TIG and MIG welding are most popular gas shielded arc welding processes used on many industrial fields. MIG welding is high efficiency process compared to TIG welding, however it is needed to improve the quality about spatter and weld metal toughness for advanced GMA process. Although pure Ar shielding gas is desirable for weld metal toughness, MIG arc is unstable in pure Ar shielded condition due to the irregularly behavior of cathode spot on plate surface and suitable welding execution is difficult. We found that MIG arc becomes stable even though in pure Ar shielded condition by simple hybridization of TIG and MIG. Therefore, this process has high possibility as new type of high quality and high efficiency welding process. In this study, we investigated the influence of hybridization condition such as TIG-MIG current balance, distance between the both arcs and torch angles on stabilization of the process and confirmed the suitable range of the condition. The main results are as follows: (1) TIG current is needed to be larger than MIG current for stabilization of MIG arc. (2) According to increase of the distance between the both arcs, MIG arc shows high arc voltage and becomes unstable. (3) On the condition of small angle between the both torches, as thirty degree, MIG arc is deflected toward back by repulsion with TIG arc and bead shape becomes convex.
Cemented carbides (WC-Co) that consist of tungsten carbides and cobalt have been utilized preferentially for cutting tools. However, since cemented carbides are made of rare metal, establishment of the technology for reuse and recycling are earnestly desired. If cylindrical shanks that the cutting edges are cut off can be combined with each other, it is possible to reuse those shanks as new cutting tools. Till today, joining method generally used for shanks is brazing. But, the joining strength of brazed joints tends to be rather weak for being used as cutting tools. In our previous study, cemented carbides were successfully joined by the diffusion bonding. The strength of joints by the direct diffusion bonding at bonding temperature 1200°C was almost equal to the strength of base material. However, since there are some cases of using cemented carbides with polycrystalline diamond for bonding, the temperature of 1200°C can be too high. In this study, on the assumption that the strength of the diffusion bonding was higher than that of the brazing, to lower the bonding temperature, a feasibility for applying the diffusion bonding between cemented carbides using Ni or Co as interlayer was fundamentally verified. The strength of joints with interlayer by the diffusion bonding at the bonding temperature 1100 - 1000°C was stable and equal to the strength of brazed joints. Co interlayer was more effective than Ni interlayer. And the feasibility of the diffusion bonding with interlayer was clarified.
Intergranular cracking due to liquid zinc embrittlement has sometimes occurred in heat affected zone (HAZ) of dissimilar welded joints of austenitic stainless steels with galvanized or zinc-plated carbon steels. In order to make clear the governing factors of cracking due to liquid zinc embrittlement in the heat affected zone of austenitic steels, the effect of chromium and nickel contents in the alloys on the intergranular zinc penetration was investigated in this study. From the results of the self-restraint U-type hot cracking test for zinc-coated austenitic alloys, the cracking susceptibility drastically changed at the certain value of the chromium/nickel contents. Especially, compared liquid zinc penetration behavior into grain boundaries between type304 stainless steel and Fe-36%Ni alloy, the zinc penetration was recognized only at grain boundaries in the stainless steel. On the other hand, the grain boundary energy in type304 stainless steel at elevated temperatures was about two times higher than that in Fe-36%Ni alloy. >From these results, it was concluded that the difference in susceptibility to intergranular cracking caused by liquid zinc embrittlement among alloys with various chromium and nickel contents was attributed to the change in grain boundary energy in these austenitic steels.
The objective of this study is to ensure the safety of nuclear reactors. A number of accidents occurred from the welded zones at pipe penetration points of the reactor vessel or in coolant pipes have been reported at sites around the world. One of the main causes of such leaks is welding residual stress. It is therefore very important to know the welding residual stress in order to maintain the safety of the plants, estimate plant life cycle and design an effective maintenance plan. Welded joints in nuclear reactors have complex shapes, and the welding residual stresses have complex three-dimensional distributions. In this study, the mock-up is idealized and manufactured for the welded joint at the pipe penetration part of actual reactor vessel. The inherent strain method is applied to measure the welding residual stress of the joint accurately. The inherent strain method is an analytical method which solves an inverse problem using a least squares method. For more accurate estimation, the robust estimation is applied to the inherent strain method. As one of the robust estimation methods, the least squares method with cut is used. The data of the measured strains are selected, based on the residuals. First, all data are used in the analysis. Some data which have large residuals are cut, and the next analysis is performed, using the rest of the data. Such calculation is repeated until a convergence condition is satisfied. A concrete procedure of the calculation is proposed. The welding residual stress of the joint is analyzed by such robust estimation method. As a result, high-accurate estimation is achieved. The significance of the result is discussed in detail.
In a gas metal arc (GMA) welding process, a consumable wire is fed as an anode electrode of the arc, and then a wire extension and an arc length change simultaneously. Arc phenomena depend on the wire extension and the arc length. Therefore, understanding of dynamic characteristics of GMA welding is important. In the present model of GMA welding with a constant voltage characteristic, the wire extension and the arc length change by a balance of a wire feed rate and a calculated wire melting rate. We simulate dynamic characteristic of GMA welding when a setting voltage and a wire feed rate change, and clarify effects of the variation of the wire extension and the arc length on an arc phenomena. A self-adjusting arc welding is presented by our numerical simulation.
We study about effects of metal vapor on arc plasma and heat source properties in a gas metal arc (GMA) welding by a GMA model considering behavior of metal vapor. The metal vapor from a weld pool is swept away towards surrounding of arc plasma. On the other hand, the metal vapor from a wire is mixed into arc plasma, and then, arc center is dominated by metal vapor. The highest temperatures occur at the edge of the arc center. Because metal vapor have strong radiation, energy loss of radiation becomes large. In GMAW process, temperature of arc plasma is low because energy loss of radiation is large at the arc center.
It is recognized that the fatigue properties of weld joint is successfully enhanced by mitigating the stress concentration at weld toe with smotherning the profile, as well as managing the residual stress at the weld toe. To attain the desireble weld toe profile without deteriorating the productivity of manufacturing processes, the development of welding process consisting of the CO2 gas shielded arc welding as the leading electrode and plasma arc welding as trailing electrode was studied. Through the obsevations of welding arc and weld pool of the bead-on-plate welding experiments using high speed video, it was found that the polarities of the leading CO2 gas shielded arc welding and trailing plasma arc welding electrodes take an important role on the management of weld toe profile. When the leading CO2 gas shielded arc welding and the trailing plasma arc welding are both electrode negative (EN), the arcs of those attracted each other and the molten metal was dammed up between those arcs, promoting the sideward flow, which resulted in a wide and low profile of the weld bead with the obtuse adge of weld toe. Moreover, offsetting the trailing plasma arc welidng was effective on the smoothening the weld toe profile on the offset side, deliverately limiting the flow of molten metal on the offset side. The effect was verified with the lap-fillet welding of 3.2 mm thick 780N/mm2 grade steel sheet. The developed welding process, plasma-arc hybrid welding, exhibited the improved weld toe profile, in terms of the carvature radius and frank angle, and the fatigue strength approximately twice as much as that of conventional CO2 gas shielded arc welding.
SnO2 has been promised as a substitutional transparent film for ITO. In order to decrease the resistance of sputtered SnO2 electrode, effect of crystallinity on carrier mobility was investigated for the sputtered SnO2 films. In this research, electronic structure (especially band structure and charge density) of SnO2 with first-principles calculation on quantum theory was clarified. Thereby, the validity of doping and crystallinity in (110) to making low resistance was founded. Besides, application of the seed layer of CVD SnO2 thin film with high crystallinity lowered the resistance of SnO2 of sputtered film.
As a reflective film material, Ag has the highest reflectivity in the visual light range (400-800nm) and is used in many cases. However, Ag is a thermally active material and we have concerns about the decrease in reflectivity by aggregation. In this study we investigate an ultra high heat proof protective layer for a thin Ag reflective film. Conventionally, SiO2 thin film is used as a protective layer for Ag reflective film. But it is difficult to obtain heat proofing > 723K. In this research we consider a SnO2 protective layer which combines high heat proofing and high crystallinity. We formed a SnO2 protective layer on an Ag thin film under various conditions, and investigated its heat proofing characteristics. We succeeded in obtaining ultra-high heat proofing exceeding 723K using 5 nm protective layer. Furthermore, in trying to understand the mechanism of this outstanding high heat proofing reflective film system, it became clear that the crystallinity in high temperature diffusion plays a major role.
In this paper, metal transfer modes of mild steel wire of 1.2 mm in diameter, which were observed for welding variables of current, voltage and polarity in Gas shielded Metal Arc Welding process with four kinds of shielding gases (Ar, He, CO2 and mixture gas of Ar+20%CO2) are described. In electrode positive polarity, metal transfer transition from globular to spray occurs with use of shielding gas of Ar or Ar+20%CO2. But with shielding gas of He or CO2 only globular transfer was observed. In electrode negative polarity, mild steel wire added by a very small amount of Rare Earth Metal, which promotes electron emission at the cathode, makes globular to spray transition possible with shielding gas of CO2 or Ar+20%CO2. Other combinations of shielding gas and electrode wire result in globular transfer in the current range up to 400 A. In spray transfer mode, current density was estimated to be higher than 1×108 A/m2 at the surface of metal drop onto detachment.