The research presented here is aimed at clarifying some basic heat transport mechanisms in argon-helium gas tungsten arcs. Two factors that are of great importance in the heat balance of the arc and still lack understanding are the radiative power loss and the anode fall voltage. In this research, Langmuir probe experiments were performed to estimate the anode voltage drop. The radiative power production of the arc was measured using a commercial radiation power meter. From the results of the Langmuir probe experiments it was found that the anode voltage drop and the electron temperature at 1.5 mm above the anode are fairly constant up until helium contents of 75%. Only when pure helium is used as a shielding gas, the anode voltage drop rises considerably. As the radiative power production of a plasma is directly linked to its electron density, the electron density profiles were measured using a new method based on IR radiation first proposed by Ohji and Eager. The radiative power of the arc decreases considerably when introducing helium into an argon arc. The radiative power in pure helium arcs is one order of magnitude smaller than in pure argon arcs. When inserting a high pass filter with a 600 nm cut-off wavelength, the measured power in helium arcs is even more drastically reduced compared to that in pure argon arcs. Furthermore, the maximum electron densities found in arcs containing helium are too low compared to theoretical values calculated from the Saha equation.
An analytic model estimating the natural frequency of a weld pool is derived using energy method. The model is applied to the complex weld geometries, penetration conditions and oscillation modes. In addition to partial and full penetration, transition penetration is introduced and analyzed as the intermediate state between partial and full penetration conditions. Results show that the predicted natural frequency of the weld pool is affected by oscillation modes and geometric parameters such as the eccentricity and sidewall slope of the weld pool as well as material properties and pool dimensions.
It has been considered that the anode of TIG arc is a disc of a certain diameter, and the arc is always stable and stand still, and that the weld dimension is determined by a set of welding conditions indifferent to the steel composition. This conviction was upset by the finding that minor element such as O and/or S influences penetration greatly. Okada observed that the metal composition influences anode pattern and penetration. Aim of this experiment is to clarify the precise shape and behavior of He arc anode, by means of electric potential measurement of base metal and arc atmosphere, developed by Okada, and video observation. Anode pattern changes according to arc length, current and S% of steel, and its movement coincided well with potential curve. Discussions were given on the effect of various factors on the anode behavior and convections in the weld pool.
As reported in the previous papers, the high current AC-MIG welding process has been successfully applied to butt welding of sheared plates in a steel pipe mill. The author has improved the AC-MIG process to a further high efficient one that employs two electrodes in tandem providing one molten weld pool. An attempt has been made to apply this improved process to seam welding of UO pipes for the frigid zone use together with a SAW process. It has been found that the new process gives deep penetration exceeding 5 mm in the root pass and sufficiently melts grooves to provide wide weld beads so that 1 m/miri welding velocity two times higher than that by the previous processes can be obtained even under highly varying groove width conditions.
The previous papers have reported that the high current AC-MIG welding process is superior to the conventional DC-MIG process in the welding efficiency as well as the welded joint performance. The authors have employed the AC-MIG process to weld heavy steel plates of a 980 MPa tensile strength level. The weld metal with very low hydrogen content was obtained by the new process, resulting in lowering preheat temperature in high strength steel welding. Second, the AC-MIG process made welding arc climb during an electrode negative polarity. This phenomenon is preferable in narrow gap welding. Furthermore, AC-MIG weld metal contained low oxygen and thus, high toughness resulted. As a result, a narrow gap AC-MIG process was developed to provide high efficiency in processing and metallurgically high quality welds in welding of 980 MPa high strength steels for pressure shafts in hydropower stations. The welding wire with chemical compositions satisfying the suitable strength and toughness was produced. Also, the appropriate welding parameters were determined for the narrow gap welding of pressure shafts.
Penetration form and welding of practical joint of SUS 304 in traveling DC TIG arc welding are investigated. Welding bead with large penetration ratio (penetration depth/bead width) can be obtained in low speed welding. In particular, since the anode-spot is fixed at the center of the molten pool in He-DC TIG, deep penetration with narrow bead width is effectively formed. Transition current, in which bead width of face side has the minimum value under penetration bead (uranami bead) formation, increases in Ar arcs as the thickness of the base metal increases. Step movement welding method, in which stationary arc is struck after traveling in a short distance, is effective to obtain stable uranami bead in the plate thickness above 6 mm. Moreover, when flux-cored wire is applied to this method, stability of uranami bead formation is more improved.
Vibration of molten puddle is achieved with the low frequency pulsed MIG welding process of new current waveform to switch over two preset unit pulse conditions alternately. In this paper, beneficial effect of reducing the blowholes which often cause problems in MIG welding of Al and its alloy was investigated by using above mentioned process under 99.9%Ar-0.1%H2 shielding gas atmosphere. It was made clear that switching frequency of unit pulse conditions in the range of fs=10-25 Hz had beneficial effect of reducing blowholes on various wire-base metal combinations, welding speed and flat, vertical-up and horizontal positions. Moreover, this process was effective in reducing the blowholes for Al cast alloy.
Austenitic stainless steel foils having thicknesses of 100μm and 50μm were seam welded to make an seam bond with an insert metal of a Ni base amorphous foil. The weldability has been investigated in comparison with seam welds without the insert metal. Main results obtained are as follows: (1) The seam bonds of 100μm thick stainless steel foil were obtained even if the insert metal was not used, however, the seam bonds of 50μm thick stainless steel foil were obtained only when the weldings were performed with the insert metal. (2) When the amorphous foil was used as the insert metal, the welding current range that seam bonds were obtained was wide in comparison with the seam welding without the insert metal. (3) The microstructures of the seam bonds with the insert metal were divided into three types by the solidification morphology of melted zone of the insert metal and the stainless steel foil. (4) The maximum peel load of the seam bonds without the insert metal largely fluctuated, however, that of the seam bonds with the insert metal hardly fluctuated. (5) When the peel test and the tensile shear test were carried out for the seam bonds, the fractures occurred in the stainless steel foils near the seam bonds.
Explosively welded Al/Cu clad is tried to be fabricated inserting Cu intermediate plate between Al driver and Cu base plates. In explosively welded Al/Cu clad using conventional method, generation of excess reacted interfacial zone caused the degradation of the bonding property. The use of Cu intermediate was effective as a mean of decreasing the energy dissipated by collision. The effect of kinetic energy lost by collision on the thickness of reacted interfacial zone and on the bonding strength were examined using small size experiments. Al/Cu electric transition joint with commercial size are tried to be fabricated by the use of Cu intermediate plate and the bonding property was fairly improved compared with it made by conventional method.
Properties of surfacing weld metals by MIG and TIG processes have been investigated using newly developed Al-Cu seamless type cored electrode wires of 1.2 mm in diameter. Three kinds of Al-Cu cored wires of 40, 45 and 70% Cu contents were tested on base plates of aluminum alloys of types A1050P (Al), A5083P (Mn-Mg-Al), A7075P (Cu-Mg-Zn-Al) and AC4B (Si-Cu-Zn, cast). The conclusions are as follows. Hardness values at room temperature of HV220-260 on A5083P and A7075P and HV200-220 on AC4B were obtained in the transverse cross sections of the bead weld made by MIG and TIG processes. The weld hardness increased in proportion to the Cu content in the weld metal on the A1050P base plate and hardness of HV300 was obtained in crack free condition with Cu content of 52%. Cracking in the weld metal occurred when the Cu content in the weld metal exceeded 54%. Hardness measurement at elevated temperatures up to 400°C revealed a moderate decrease in hardness, but a rapid decrease at over 200°C. Deposition rates of MIG and TIG processes are 30-40gr/min at 120-180A, 5gr/min at 100-140A, respectively. MIG process may be, recommended for weld surfacing, while TIG process for hardening of base metal. Results of wear resistance test, pin-on-disk test, of weld metals made with Al-40Cu and Al-70Cu cored wires indicated improved resistance with increased surfacing hardness.
The authors have developed a mathematical model of heat and mass transfer in the stationary TIG arc weld pool considering four possible forces which induce streaming. They are two kinds of body forces, i.e., Electro-magnetic and buoyancy forces, and two shear stresses, i.e., surface tension and aerodynamic drag force. However, every mathematical modeling is always made under the appropri ate assumption and boundary conditions as well as some simplification. Also, one encounters problems on the lack of physical properties of material, especially at elevated temperature. Therefore, it is essentially necessary to verify the model by experiments. The present authors have conducted various model experiments for the effects of electro-magnetic force and aerodynamic drag force to verify the validity of developed model. In this paper, it was revealed the experimental results of the individual effect of electromagnetic force on the convection using a mercury pool contained in a basin with current flow and velocity distribution of liquid was measured. Also, another model experiment was performed using a wood's metal surface and electric current was flown from the soldering iron to wood's metal and the resultant penetration shape was obserbed. In both model experiments, the coincidence of calculated and experimental model was experimentally verified.
Anode spots configuration on the molten pool in the moving GTA was discussed from observation of slag bits behaviour with varying welding condition and base metal elements. The positions of slag bits on the pool are greatly influenced by surface flow on the pool caused by change of plasma stream direction with a little arc inclination and content level of minor elements in steels such as sulfur and oxygen. Especially, on condition that the surface flow is slow in the stationary state, the anode spot is greatly moved by a little fluctuation and irregular weld beads caused by the anode spot movement are liable to occur. On the other hand, effect of the size of anode region dispersed on the pool on melting the back of a thin steel plate was discussed. The anode region size is greatly influenced by arc length and arc force (shape of tungsten electrode tip) which spread the higher temperature region of plasma, and content level of the minor elements which is reported to change directions of metal flow on the pool surface. The ratios of radius of anode region to radius of the pool in a stationary arc with arc length of 3 mm are 0.73 under the condition of the lower content level and 45 deg. conical tip, 0.64 under the condition of the same content level and truncated conical tip, and 0.61 under the condition of the higher content level and 45 deg. conical tip.
In this report, the friction welding conditions for commercially pure titanium/pure aluminium joint were developed, and the effect of post-weld heat treatment (PWHT) on the mechanical and metallurgical properties of the complete friction welds was examined in basic research. The friction welding conditions range, which can produce the complete weld joints having more than 100% joint efficiency as joint tensile property and excellent bend ductility in the as-welded conditions, was clarified. PWHT temperatures including up to 873 K (600°C) for 36 ks (1 H) had no influence on joint mechanical properties, especially, joint tensile and bend ductility. However, they drastically decreased during PWHT at 873 K (600°C) for more than 72 ks (20 H). X-ray diffraction analysis and SEM observation confirmed that those reductions were due to the formation of large contents of Al3Ti intermetallic compound phase at the pure titanium/pure aluminium interface. The critical width of Al3Ti phase (at PWHT of 873K for 72 ks), which steeply reduced the mechanical properties, was around 10 μm. Several atomic percents of silicon concentrated in the Al3Ti phase.
Solidification crack susceptibility of GMA weld metal of Al-4.5%Zn-1.2%Mg A7N01 base metal has been successfully improved by combination of low frequency switching pulsed GMAW process and Zr added Al-7%Mg tentative wire. Close relationship between grain size of weld metal and crack susceptibility was observed and remarkable reduction in crack susceptibility was obtained in weld metal with fine equiaxed grains of 20 to 30 μm in diameter. This marked grain refinement can be obtained only by the combination of low frequency switching pulsed GMAW of 2.5 to 50 Hz and Zr added Al-7%Mg tentative wire. No considerable grain refinement was observed with Zr-free wire. Relationship between oscillation behavior of molten pool caused by current pulsation and grain refinement was discussed.
Brazing of AlN to metals was conducted at 1073-1293 K for 0-129.6 ks using active filler metals of Cu-22%Ti, Cu-10%Zr, Cu-15%Hf binary alloys and Ag-27%Cu-2%Ti ternary alloy. The reaction layer which was comprised of TiN, ZrN or HfN was formed at the bonding interface between AlN substrate and the brazing layer, and eutectic phases such as Cu-Cu4Ti were detected in the brazing layer when binary filler metals were used for AlN to copper joining. TiN was identified in the reaction layer of AlN-molybdenum joint brazed using ternary filler metal. The thermodynamic calculation suggested that TiN, ZrN and HfN were produced by the interfacial reaction between AlN and active metals in the melted binary filler metals.
The reaction layer growth in AlN-molybdenum joint during brazing operation was investigated at 1073-1173 K for 0-129.6 ks using Ag-Cu-Ti filler metal. The thickness of reaction layer formed at the bonding interface was increased with increasing the bonding temperature and holding time. It was elucidated that the reaction layer growth could be expressed by Johnson-Mehl type equation with time exponent 'n' of 1/2 which was derived from the parabolic growth law by considering the consumption effect of diffusing element in the reaction layer. The apparent activation energy for the reaction layer growth was 68.9 kJ/mol. It may be deduced that the bonding phenomena and mechanism of AlN to metals were similar to those of Si3N4 to metals using active brazing method.
In this research work, the effect of area fraction of M-A constituent on charpy absorbed energy (vE) of both simulated-CGHAZ (Coarse-Grained HAZ for high heat input welding process) and ICCGHAZ (Intercritically-Reheated CGHAZ for multiple welding process) of either 780 or 980 MPa class HSLA steel has been studied. The M-A constituent is classified into two types such as massive M-A and elongated M-A depending on its form. The form of M-A changes from "elongated M-A" to "elongated M-A+massive M-A" and then to "elongated M-A+massive M-A+carbide" according to the increase of cooling time, Δt8/5. Furthermore, the size of M-A increases. It has been clarified that the vE of ICCGHAZ is rather lower than that of CGHAZ as the result of dual thermal cycle test at the temperature of 1073 K where the peak temperature of second thermal cycle, Tp2 exceeds Ac1 due to the formation of massive M-A of large size. However, the vE at both 873 K and 673 K where the peak temperature of third thermal cycle, Tp3 is lower than Ac1 is improved to be more than the vE at temperature of 1073 K which is equal to Tp3 in the triple thermal cycle test. Since these improvement of vE considerably corresponds with the decrease of area fraction of M-A, the M-A constituent is decomposed by the tempering effect of third thermal cycle so that the vE value of ICCGHAZ seems to have been improved. The increase of area fraction of total M-A in both single and multiple welding thermal cycle tests causes the increase of that of massive M-A seems to be the decisive factor for the deterioration of vE in both CGHAZ and ICCGHAZ of either 780 or 980 MPa class HSLA steel.
A stress relief method using ice plug for butt weld joint of piping is described. The method is as follows. Two ice plugs are formed inside piping, and isolate a section which include weld joint. An internal pressure of isolated section increases as ice plugs grow, and it gives tensile strain to pipe wall of the section. After the pressure reaches target level, the pressure is released and the residual stress decreases. The stress relief method is named by authors as Twin Ice Plug (TIP) method. This paper described details of this process, measuring of internal pressure from outside of piping, controlling internal pressure, and the effect of stress relief. The internal pressure of isolated section is estimated by the strain measured by strain gauge on outer surface of the section. A control of a pressure of the section is done by controlling supply rate of refrigerant (LN2) and heating pipe wall. The maximum internal pressure reached in this method is 40 MPa for 4BSch4O (O.D.=114.3 mm, t=6.0 mm) stainless pipe and 22.5 MPa for 6BSch4O (O.D.= 165.2 mm, t=7.1 mm). The residual stress of as GTA weld joint of stainless pipe is measured, its maximum value is more than +300 MPa. The effects of this method are confirmed by measuring residual stress of 4BSch40 6BSch40 joints that are treated by this method. The residual stress of inside surface decreases and changes to compression, and that of outside surface also decreases to under 100 MPa.
In order to make the test standard for thermal shock resistance of ceramic coatings, both fracture mechanisms of the coating and main factors for the fracture have to be clarified. In this study, cyclic thermal shock testings were carried out on the ZrO2/NiCrAlY plasma sprayed coatings, and unsteady thermal stress analyses by FEM were also conducted on these testings. The results obtained are summarized as follows. (1) ZrO2 coatings were suddenly spalled off completely during or just after the cooling process, after some cycles of thermal shock. (2) Fracture took place at the interface of ZrO2 sprayed particles about 10μm away from the ZrO2/NiCrAlY interface. (3) From the results of unsteady FEM analyses, large compressive stress was recognized in the ZrO2 coating during the cooling process. (4) From the results of both SEM observations and FEM analyses, it was revealed that the fracture of the coating was caused by unstable propagation of internal crack which was generated at the inside of the coating layer near the ZrO2/NiCrAIY interface.
Ultrasonic bonding of Cu composite wire with Au coating at room temperature has been investigat-ed for packaging technique of thin film device unaccepted heating. Cu composite wire used in this study consists of Cu core of 44μm in diameter and Au coating of 3pm in thickness. Two kinds of bonding pads are used. One is Au plating film of 5-6μm in thickness on Au/Cu/Cr thin film deposited by sputtering on Cu substrate. Another is Au PVD film of 0.4μm in thickness on Cu/Cr thin film deposited on Cu substrate. Specimen has been bonded under the conditions of various ultrasonic power, bonding load and bonding time. For evaluation of a bonded specimen, the wire deformation and the 90 pull strength have been measured, and fracture surface has been observed by SEM. Main results in this study are as follows; (1) Adhesion and rupture take place alternately and periodically during ultrasonic bonding of Cu composite wire with Au coating. Then the joint strength also increases and decreases according to those. This phenomena is more remarkable on the bonding condition of a lower load and an upper US power, and the periodic time is shorter on that of an upper load and US power. (2) If a wire deformation ratio of squeezing size to initial diameter of wire, is controlled in the range of 40 to 60 percent, the joint strength is obtained more than 0.3 N for Cu composite wire of 50μm in diameter.