Features of microseconds arc discharge with gap spacing of micrometers, between a cathode of thin tungsten wire with sharpened tip and an anode of stainless steel plate, have been experimentally investigated. The experimental setup, which consists of a micro-arc torch, precise positioning mechanisms actuated by piezoelectric devices and pulse motors, and a power supply for discharge, was constructed. Time-resolution of micro-discharge appearance was observed through microscope with high-speed shutter CCD camera. It is shown that gap length is dominant factor of not only electrical breakdown voltage but also size and/or form of melting spot at anode surface by micro-arc.
JIS A6061P T651 (Al-Mg-Si alloy) was electron-beam-welded without filler metal and with Al-Si filler metal. Composition of crack, segregation and eutectic melting in welds was examined to clear mechanism of weld crack formation. Si content and its distribution in weld metal were investigated to find out effective Si content for prevention of weld crack. Obtained conclusion are summarized as follows : (1) Al, Si and Mg are recognized in the boundary of dendrite of weld metal and in eutectic melting of HAZ from result of qualitative analysis of EPMA. It is presumed that these elements form Al-Mg2Si eutectic alloy when filler metal is not used. On the other hand, it is also presumed that these ones form Al-Mg2Si-Si eutectic alloy in boundary of dendrite of weld metal and Al-Mg2Si eutectic alloy in eutectic melting when filler metal is used. (2) It is furthermore presumed that solidification crack of weld metal occurrs due to formation of Al-Mg-Si eutectic alloy and that liquation crack in HAZ occurrs due to formation of eutectic alloy of Al and Mg2Si in base metal. Crack is hard to occur because Al-Mg-Si eutectic alloy in weld metal fully fills in crack when this eutectic alloy of lower melting point exists in larger amount. (3) When depth of penetration exceeds height of filler metal, Si content of weld metal decreases suddenly in root area. And its standard deviation increases with its meanvalue increase. However, standard deviation decreases as the ratio of penetration depth to filler metal height approaches one. (4) Crack dose not occur when Si content of surface weld layer exceeds 1.6% and content of root weld layer exceeds 2.7%. As far as liquation crack in HAZ is concerned, it decreases with increase of Si content of weld metal. It also disappears when Si content of weld metal exceeds 4.8%.
In the present work, a three-dimensional numerical model for MAG (Metal Active Gas) welding of thin plate is developed. In MAG welding, metal is deposited into the molten pool from the electrode wire, and the metal plays an important role in determining weld bead profiles. In the model, the thermal energy enters the plates through two mechanisms, i.e., direct heating from arc plasma and indirect heating by melting wire. The transient temperature distribution on base metal is numerically analyzed in order to estimate the molten pool size by using a finite difference model based on heat flow equation, and the theoretical configuration of molten pool is calculated, taking account of the balance of gravity, surface tension and arc pressure. By using these models, the transient MAG welding process is numerically analyzed. The numerical results are in good agreement with the experimental results for bead-on-plate-MAG welds on mild steel plate. Accordingly, it is concluded that the model, proposed in the present work, is useful for prediction of MAG weld bead formations.
In the first report, stabilizing effects of a CO2 laser on a TIG arc behavior were discussed from the point of the arc voltage and of the interaction between the arc and the laser plume. In this report, the CO2 laser beam was scanned by a beam oscillator, and the shapes of melted parts of the base metal were investigated. Furthermore, the behavior of a TIG arc with a scanning CO2 laser beam was investigated by high speed video-pictures. The main experimental conditions were as follows. The TIG arc current, the laser output, the scanning frequency and the scanning width of a laser beam, the traveling speed of a SUS304 base metal and the distance between the base metal and a tungsten electrode were 100 A (DCEN), 2 kw, 25 Hz, 8 mm, 20 mm/s and 15 mm, respectively. As a result, the arc could be controlled by the scanning laser beam, and wide and shallow beads were made using this method under the suitable conditions. Therefore, it was found that the arc with scanning laser beam is excellent as heat source for surface treatment. On the other hand, the arc voltage and the range of its change decreased according as the scanning frequency increased from 5 Hz to 20 Hz. According to the observation using high speed video-pictures, the arc went straight forwards from the electrode and bent toward the scanning laser plume, and the bending point of the arc became increasingly far from the tip of the electrode when the scanning frequency increased. It would be considered that the arc voltage was affected by the bending point of the arc column because of the arc stiffness.
A numerical study of time-dependent penetration processes in stainless steel with convective forces by stationary gas tungsten arc is described. The numerical solution technique based on finite-difference method was adopted in the development of mathematical models for investigating heat transfer problem in the weld pool. The computational model consists of the transport equations and considers driving forces of fluid flow ; electromagnetic force, surface tension force, and plasma stream shear stress. Surface tension data depending on temperature and sulfur concentration were given in the calculation. It is shown that both of the penetration shape and the surface temperature distribution are affected by convective flow in the weld pool.
Visual sensing and measurement are utilized widely in the various production processes. In this visual sensing, high accurate micro sensing in the macro processing area is required. Wide field of vision is required for the visual sensing in a macro area. On the other hands, short pixel length in a pictured image is required for high accurate visual sensing. These two requirements are opposite for visual sensing by TV camera. In general, visual sensing by the plural TV cameras or movement of a TV camera is engaged for the visual sensing of the separated regions. But, these methods have significant problems in a calibration process of the optical parameters and their calibration accuracy. If the two separated region of the object works for measurement can be pictured on a same image plane of a TV camera, high accurate micro sensing in a macro view area can be realized and the calibration process will be done simply. In this research, we propose an imaging method with separated fields of vision by using a prism, and make clear the relation. between the optical parameters and the fields of vision. The distance between the pictured fields of vision is fixed by a vertical angle and a refractive index of a prism and the distance between a pictured object and a lens of a TV camera.
Welded structures are composed of a large amount of the horizontal fillet joint whereby high speed fillet welding significantly influences on improvement of productivity. The "Tandem Arc MAG Process" here referred to is a newly developed process which realizes high speed horizontal fillet welding without any undercut by means of holding a stagnant molten metal formed between two electrodes. The authors have prepared the model of a molten metal pool, and researched relations among the displacement of molten metal and solidification point along a toe of weld metal. This research has been accompanied by studies on a distance between electrodes where stagnant molten metal is stably maintained as well as on current distribution to the leading and trailing electrodes. At the same time, a welding wire has been developed, that has excellent blowhole resistance in high speed welding. As a result, high quality welds have been obtained in a welding speed about 3 times as high as that of the conventional process. The system is being applied to field work and proved that a process capability is improved to a great extent, thus the system is contributing greatly to productivity.
The diffusion-bondability of A6061 aluminum alloy to SUS316 stainless steel has been improved by using surface-activated pre-coating technique for SUS316 stainless steel. The surface-activated treatment for SUS316 was carried out by series of steps as alkaline cleaning → electrolytic cleaning HCl activating → metal-striking prior to diffusion bonding. Diffusion bonding of A6061/SUS316 was conducted at 758 K-823 K for 0.6 ks-7.2 ks applying 9.8 MPa in vacuum. ESCA analyses revealed that the surface oxide film could be removed by surface-activated pre-coating treatment and that striking insert metals would act as a barrier to reoxidation of SUS316. The tensile strength of A6061/SUS316 joints using Ag, Cu and Ni striking insert metals was risen up to about 100 MPa bonded at 758 K for 0.6 ks indicating nil joint strength in direct-bonding situation. The reaction layer growth in A6061/Ag striking/SUS316 joint was followed by the parabolic growth law, and the incubation time for reaction layer growth using Ag striking insert metal was shortened compared with direct-bonding situation.
In order to join an aluminum pipe to an iron pipe in air, we inserted the zinc-plated iron pipe into the aluminum, and heated them to given temperatures. The optimum joining conditions were determined, and the properties of a joint and the joining process were metallurgically examined. The results obtained are summarised as follows. An aluminum pipe could be joined successfully to an iron pipe in air by zinc-plating on the faying surface of the iron pipe. The strength and the bonded area of the joint increased with the bonding temperature and inserting rate of the pipe. Al-Zn eutectic liquid, which formed by the reaction between Al and δ phase (FeZn8), acted mainly as filler metal in this joining system. As the joining temperature was higher, the amount of eutectic liquid formed at the interface increased, resulting in the increase of bonded area. As the inserting rate increased, the joining process finished within shorter time and the supply of Zn from δ phase continued till the last stage of the joining. Consequently, sufficient eutectic liquid for joining was formed and the joined area increased.
The oxides at the diffusion-bonded interfaces of a pure aluminum and Al binary alloys (Al-Mg (0.6-2%), Al-Si (1%), Al-Mn (0.5%), Al-Zn (1%), Al-Cu (1%)) have been investigated by transmission electron microscopy in order to examine the effect of their morphologies on the bond strength of the joint interfaces. As the bonding temperature and Mg content were increased, the strength of the joint interfaces of the Al-Mg alloys increased to levels not less than that of the base metals, and the interfacial oxide altered from continuous amorphous films to dispersed crystalline particles of Al2MgO4, and MgO. For the pure aluminum and the alloys, other than those of the Al-Mg system, the strength of the joint interfaces was much lower than that of the base metals at all bonding temperatures employed, and the interfacial oxide remained as amorphous films. These results suggest that the amorphous oxide film prevents an increase in the strength of the diffusion-bonded interface of the Al alloy and that strengths comparable to those of the base metal can be obtained, when almost all amorphous films alter to crystalline particles. When the foils of the Al-Mg alloys were applied as an intermediate layer, the bond strength of the joints of the pure aluminum and the alloys, other than the Al-Mg alloys, was improved significantly, and the oxides at the bond interface became crystalline particles in the same way as those observed in the joints of the Al-Mg alloys. Considering that the morphological change of the interfacial oxide described above can be explained as a consequence of the reductive reaction with Mg, as reported in a previous paper, it can be concluded that the addition of an element having strong affinity to oxygen, like Mg, into the intermediate layer as well as the base metal can improve the bond strength of the joint interface by changing the morphology of the interfacial oxide from amorphous film to crystalline particle.
Mechanism of hot cracking, especially ductility-dip cracking in HAZ during repair welding was investigated using modified HP-type heat-resistant cast alloys. The change in hot ductility was evaluated with the reduction of area at 773 K by the Gleeble test. The hot ductility of each alloy was almost at the level of 20% in as-cast situation, while decreased with aging and fell down below about 8% after service exposure or long term aging at elevated temperature. Microscopic observation revealed that the brittle fracture occurred in service exposed alloys, and that cracks initiated and propagated preferentially through microconstituents. Hot ductility was decreased remarkably with increasing the amount of microconstituents on dendritic boundary, and with proceeding the phase transformation of microconstituents as NbC → η phase or M23C6→G phase. It was deduced that the hot ductility would be deteriorated by the stress concentration in microconstituents and/or the plastic constraint on dendritic grain due to the formation of continuous network of microconstituents surrounding the dendritic boundary. It follows that ductility-dip cracking susceptibility during repair welding was enhanced by the reduction of hot ductility.
The reaction between Br resins and Au4AI intermetallic compound layer at the Au-Al bond interface has been observed when the semiconductor device is used at high temperatures. Au4AI is annealed at 573 K for 2 hours with Br resin encapsulation, and microstructures and chemical compositions of the corroded layer have been investigated with TEM and EDX. In the corrosion layer, black island-shape phase with fcc structure and white amorphous phase have been found out. The former one was considered to be Au phase and the latter one amorphous phase of Al-Br-O system. The hardness of the corrosion layer and the Au4AI are 98 Hv and 192 Hv, respectively. Therefore, it can be considered that the formation of the Au phase and the Al-Br-O amorphous phase contribute to the reduction of the mechanical property during the annealing.
Degradation of weldability caused by helium, which is generated by nuclear transmutation in neutron irradiated material, is an important issue to be addressed in planning of proactive maintenance of light water reactor core internal components. In this work, the weldability of neutron-irradiated stainless steel and nickel-base alloy, which are major constituting materials for components, was practically evaluated. The weldability was first examined by TIG welding in relation to the weld heat input and helium content using various specimens (made of SUS304 and SUS316L) sampled from reactor internal components. The specimens were neutron irradiated in a boiling water reactor to fluences from 4 × 1024 to 1.4 × 1026 n/m2 (E>1 MeV), and resulting helium generation ranged from 0.1 to 103 appm. The weld defects were characterized by dye penetrant test and cross-sectional metallography. The weldability of neutron-irradiated stainless steel was shown to be better at lower weld heat input and lower helium content. To evaluate mechanical properties of welded joints, thick plates (20 mm) specimens of SUS304 and Alloy 600 were prepared and irradiated in Japan Material Test Reactor (JMTR). The helium content of the specimens was controlled to range from 0.11 to 1.34 appm selected to determine threshold helium content to weld successfully. The welded joints had multiple passes by TIG welding process at 10 and 20 kJ/cm heat input. The welded joints of thick plate were characterized by dye penetrant test, cross-sectional metallography, tensile test, side bend test and root bend test. It was shown that irradiated stainless steel containing below 0.14 appm of helium could be welded with conventional TIG welding process (heat input below 20 kJ/cm). Nickel-base alloy, which contained as much helium as stainless steel could be welded successfully, could also be welded with conventional TIG welding process. These results served as basis to evaluate the applicability of repair welding to actual reactor components.
In order to clarify the stress/strain distribution across the joint interface of friction weld between pure titanium (Ti) /pure aluminium (Al), the characteristics of the joint interface have been investigated in view of ultrasonic leaky surface acoustic (Rayleigh) wave velocity (VR) and hardness distributions across it. Especially, one of the first efforts is focused on whether a mechanical scanning acoustic microscope (SAM) can be utilized to measure the VR distribution across the interface or not. The effect of tensile/compressive strains on VR of Ti and Al substrates, the relation of crystal direction versus VR for single crystAl pure Al substrate, and VR distribution across as-welded and post-weld heat-treated Ti/Al friction joints have been investigated by using a SAM. As for Ti and Al substrates, all direction (isotropic) VR (AVR) decreased when the applied tensile strain increased in elastic deformation region, however, they increased as increasing applied strain in plastic one. Compressive strain slightly affected the change of AVR versus in both elastic and plastic deformation regions. Uni direction (anisotropic) VR (UVR) increased as increasing tensile and compressive strains for Ti substrate. While UVR of Al substrate decreased with increasing of tensile strain, it increased for compressive strain. There was clear relation between UVR and crystal direction of single crystal pure Al substrate, and the highest UVR was obtained at the direction parallel to the most close-packed crystal direction of fcc metal (). In case of as-welded Ti/Al friction joint, the scatter of AVR distribution was relatively high overall the measured region, and AVR of Al substrates adjacent to the joint interface was relatively high. It was thought that this high AVR was resulted from high plastic strain generated during friction weld operation. The scatter of AVR distribution was reduced and the high AVR was not observed when the joint was post-weld heat-treated. While axial direction UVR of Al substrate adjacent to the joint interface was extremely high in as-welded condition, that of radial direction was not high. Those of Ti side were not high in as-welded joint. The VR distributions were relatively similar characteristics to hardness and calculated stress/strain distributions.
The box section welded members were made by using low transformation temperature welding material without preheating and postweld heat treatment. The expansion of weld metal due to the transformation from austenite to marensite around room temperature induced the compressive residual stress of-159 MPa along the weld line. The fatigue strength at 2×106 cycles was improved about 1.3 times as large as that of a usual box section welded member. The blowholes of which size was up to 4.5 mm did not induce the fatigue crack in the compressive residual stress field.
Fatigue crack propagation (FCP) tests have been conducted using CT specimens cut from mash seam welded joints coupled with two different steels, cold rolled low carbon steel and high tensile strength steel. FCP rate for two different directions, paralled and normal to the weld, were determined. In both directions, the FCP rates for the welded joints were considerably lower than those for the unwelded base steel regardless of the coupling of steel and slightly decreased FCP rates were seen within the weld zone in the FCP direction normal to the weld. After allowing for crack closure, the welded joints showed almost the same FCP behaviour as the base steel, indicating that the higher apparent FCP resistance were mainly due to compressive residual stress resulting from the welding. The differences in FCP behaviour between mash seam and laser welded joints are discussed on the basis of material property changes.
This paper describes a procedure proposed for fracture toughness evaluation of pressure vessels in use. A small-size specimen of thickness B=2.5 to 5.0 mm with a couple of hard zones enclosing a notch is presented. Main attention is focused on how to create the hard zone in the small-size specimen. Preliminary FE-analysis indicates that the distance e from the hard zone to notch plane and the strength ratio Sr=σYH/σYB are major controlling factors of the near notch-tip constraint, where σYH and σYB are the yield stresses of the hard zone and base material, respectively. In order to obtain a sufficient plastic constraint, the e and Sr should be e<0.16B and Sr>2. The CO2 laser welding is effective to realize such constrained state of specimens. The laser welds are hard enough and a rectangular hard zone can be created under a selected welding condition. The peak temperature in the region sandwiched by the laser welds is less than 200°C, and the level of welding residual stress is at most ± 100 MPa. Accordingly, the influence of laser welding on the mechanical and metallurgical properties of the test region is very marginal. The fracture toughness test verifies the validity of the small-size specimen with the laser welds. The fracture toughness measured by the small-size specimen is almost identical with the toughness of the full-thick specimen of base metal.
One of the tipical ways of conecting and tightning use a scrwe. A malfanction doesn't happen if an appropriate connection can be done. But, deterioration by the moisture and Pollution make the contact load of the connection spot in the direction of the decrease by the long use in the connection spot. In such a case, it knows that the occurrence of heat generation at the connection well. Generaly the heat is not know that a local heat generation with high temperature (about more than 1000°C) follows the fact the heat generation. We name the generation of heat phenomenon "a hot zone phenomenon", and we are studying it. A connection spot becomes high temperature in the long time while current is being supplied electric power once hot zone phenomenon occurs. These things cause the mis-operation of the machine and the cause of the trouble. In the worst case, A hot zone phenomenon causes a fire by the condition. it is the report that it is stuck independently and it has it about each of the various phenomena about the hot zone phenomenon. Independent phenomena are two of the electric character with the visual observation. It has it about the method to choose the combination of the connection part metal as the optimum. The combination of the metal is applicable to which circuit of the D.C. circuit, the A.C. circuit and the high frequency circuit as well. It will be able to be helped in this report's saving it from many electric accidents and the trouble.
The wear phenomenon occurs in most parts of the industrial machines by dynamic contacts between the parts and collisions with powder like a ash. The wear causes deterioration of the performance of the machines. The wear resistance materials have been developed by a thermal spraying, an overlaying, and various methods of the casting etc. In this study, composite materials consisting of alumina ceramics beads or hard metal beads and copper as a matrix were developed using HIP method. The influence of the HIP processing condition on bending strength and abrasive wear characteristics of the composites were examined. Main results obtained are as follows. (1) The separation of the alumina beads from the alumina-reinforced materials during grinding process was decreased largely when the composites were made of Ti-coated alumina beads treated by an attritor. (2) Though three point bending strength of the alumina-reinforced materials varied considerably, the maximum bending strength was greater than 200 MPa. (3) Cracks were initiated in the alumina beads of the alumina-reinforced materials during HIP processing. However, the cracks were decreased when the pressure of the HIP was lowered to 5 MPa. (4) The bending strength of the hard metal-reinforced materials varied from 360 to 580 MPa. It was higher value than that of the alumina-reinforced materials. (5) The abrasive volume loss of the composite with the Ti-coated alumina beads was about 1.8 times lower than that of the composite with the alumina beads without the attritor treating. The abrasive volume loss of the hard metal-reinforced materials was about twice lower than that of the alumina-reinforced materials. (6) The abrasive wear characteristics of the alumina-reinforced materials and the hard metal-reinforced materials were strongly superior to those of the copper.
In order to obtain the fundamental characteristics of the plume sound induced during Nd : YAG laser drilling, the relationship between the sound pressure level and laser oscillating method, laser processing conditions were investigated and the frequency spectrum analysis was also done. The sound pressure waveform and frequency spectrum relate to the oscillating method, that is to say, the frequency spectrum, which is induced by Q-switch laser, consists of continuous spectrum such as white sound and n×fQ (n: 1, 2, 3, …, fQ : Oscillating frequency of Q-switch laser), the one induced by CW laser, contains only the continuous spectrum. The sound pressure level was influenced by laser processing conditions. Further, it could be estimated that the relationship between the sound power (W) and the reaction force (FPl) could be expressed as W∝FPl2. Based on the results above, it can be expected that the useful informations about process monitoring can be obtained from the plume sound.
Deformations caused by cutting and edge welding have been measured in order to make clear an equation estimating the deforamation of cutting. The deformation was calculated from distributions of inherent strain obtained from the sequential removal of layers. Many reserachers believed that the deformation of cutting is estimated by the predictive equation for the deformation of edge welding. However, it is shown that deformation occured by cutting is smaller than one of edge welding in the same rise of average temperature. The difference in deformation is caused by thermal cycles in the vicinity of heat souce derived from the cutting process in which melting parts sprays into the air.