Oxygen plasma arc cutting characteristics and cut surface quality factors are discussed in this paper. It has been carried out to cut the SS400 workpieces with various plate thicknesses. Such measurements as top and bottom kerf widths, bevel angle, straightness, dross attached level and cut surface roughness are used to evaluate the cut surface quality. A new classification method of the dross attached level, by which the dross attached level is classified into three kinds of states, is put forward. Influence of cutting conditions on cut shape and cut surface state is investigated in detail. With the increase of cutting speed and the decrease of arc current, kerf width decreases, bevel angle increases, while straightness varies within a variation range of about 0.2 mm for the thicknesses of 3.2 to 8.0 mm. And compared with top kerf width, bottom kerf width more rapidly decreases. Moreover, with the increase of cutting speed, the cut surface roughness exhibits a slight drop regardless of arc current, and under the present conditions the smoother cuts of Rz less than about 40μm are obtained. It is proved that the dross attached state bears relation to not only cutting heat input, but also arc current and plate thickness. There are two dross attached areas, respectively, occurring under low and high cutting heat inputs. The heat input range obtaining the dross free cut varies with plate thickness. The dross free area gets wider when cutting current increases. Furthermore, it has been made clear that kerf width and bevel angle are approximately in linear proportion to the logarithm of cutting heat input for a given thickness, respectively. A vertical cut can be available under high cutting heat input.
Two Nd:YAG laser beams were condensed separately and combined at surface of workpiece in order to increase weld penetration depth. Welding characteristics were evaluated by penetration depth and penetration shape in bead-on-plate tests. Transition from penetration with one bottom to penetration with two bottoms occurs as function of welding condition. Penetration with two bottoms might be a sufficient evidence in favor of keyhole bottom separation. A close study of keyhole bottom separation is necessary to understand the increase of weld penetration by multiple laser beams combined. This paper is intended as an investigation on factors of keyhole bottom separation. The authors found that factors of keyhole bottom separation are angle of incidence of laser beams, laser power density, heat input, distance between two laser beams on a surface of workpiece, and welding position. Keyhole bottom separation occurs under conditions determined by high power density of one laser beam and high total heat input, such as 1500 W/mm2 and 104J/cm, respectively, at angle of incidence of 30° in welding using two CW laser beams in combination.
The intermetallic compound coating made by a laser and plasma hybrid spraying has been studied. The laser plasmahybrid spraying system (LPHS) was constructed with a 5 kW CO2, laser and a low pressure plasma spraying equipment. In this system, the plasma sprayed layer was rapidly remelted and solidified by the CO2 laser irradiation. It is possible to synthesize intermetallic compound coatings from the simply mixed powder using this system. To improve the cavitation erosion resistant of Ti-alloy, a NiTi coating on the Ti-alloy is investigated. The NiTi intermetallic compound is known as an erosion resistance material. In a case of only plasma spraying process, Ti and Ni particle were separated mutually in the coatings, but by the laser plasma hybrid spraying, Ni-Ti intermetallic compound was formed in the coating. And the coating was joined metallurgically with substrate and contained few defects. The ratio of phases, such as NiTi, NiTi2 and Ni3Ti was varied with the laser irradiation conditions and powder mixed ratio. To evaluate the erosion resistance of coatings, vibratory cavitation erosion was evaluated. The cavitation erosion resistance of the coatings was about 70 times as much as Ti-6Al-4V substrate.
The objective of this study is to clarify the effects of materials hardness, thermal conductivity and faying surface roughness on the bonding strength of the dissimilar-metal joint performed with ultrasonic welding process. The employed combinations between the dissimilar metals were of aluminum-copper and aluminum-austenitic stainless steel (SUS304). The following results were obtained in this study. The strength of the joint between aluminum and copper with high thermal conductivity was decreased with increasing the surface roughness of the metal having higher hardness, the copper in this case, and with increasing the thickness of the surface oxide film of the metals. When SUS304 with low thermal conductivity is welded to aluminum, a reliable joint can be achieved despite the condition of the faying surface. This is attributed that the oxide film on the aluminum surface is easy to be broken because the considerable increase in the temperature at the welding interface due to the low thermal conductivity of SUS304 makes the aluminum more plastically deformable.
In this study, the effect of oxide film on the strength of the dissimilar-metal joint performed with ultrasonic welding process was investigated. Furthermore, we examined the fracturing behavior of the thick oxide film, which was anodized on the aluminum surface, during ultrasonic welding between aluminum and copper or SUS304, and presumed the joining process. The obtained results are as follows. In the joining of aluminum-copper, the strength of the joint decreases with increasing in thickness of the oxide film on the copper surface. However, the increase in the thickness of the oxide film on the aluminum surface has no effect on the strength of the joints of aluminum-copper or aluminum-SUS304. At the welding interface of aluminum-copper, the aluminum oxide film is partially broken and the welded area is gradually increased as welding time increases. In the case of aluminum-SUS304, the aluminum oxide film is broken over the whole area of the interface at the initial stage of welding, and the welded area and the joint strength increase abruptly.
A freely falling experiment, in which a metal droplet fell freely and impinged on a flat substrate, was conducted as a simulation of the thermal spray process. The effect of substrate temperature on the flattening and solidification of the droplet was mainly investigated in this study. The transition of the splat pattern was recognized in the experiment, that is, the splat morphology of Ni and Cu droplet on the room temperature substrate was splash-type, while that on the high temperature substrate was disk-type. The cross section microstructure of the splat on the room temperature substrate was composed of an isotropic coarse grain, while that on the high temperature substrate was quite fine columnar structure. As the mean interparticle spacing in the splat changed transitionally with the substrate temperature, the solidification rate in the splat on the high temperature substrate was higher than that on the room temperature substrate. The unique porous microstructure and flowing pattern were observed in the bottom surface of the splat on the room temperature substrate while the flat microstructure without pore was recognized in that on the high temperature substrate. The difference of the solidification rate between these two kinds of splats seems to be attributed to the interface microstructure between splat and substrate. From the results obtained in this study, it can be concluded that the quite rapid solidification occured at the interface between splat and substrate when the droplet impinged on the cold substrate surface.
The role of electrochemical reaction between solder and base metal in soldering flux has been investigated in relation to wetting. The effect of silver addition to Sn-Zn lead-free solder on the wettability of copper base metal was studied by electrochemical measurement in soldering flux.The research includes the electrode potential measurement, anodic and cathodic polarization, and contact polarization between solder and base metal in soldering fluxes. The difference of electrode potential between solder and base metal in soldering flux plays an important role to remove oxide film by contact polarization. It is concluded that the electrode potential of Sn-based lead-free solders should be lower than copper to obtain good wettability, because the anodic dissolution of tin by contacting the copper base metal enhanced the wettability by removal of tin oxide which is one of the stable oxide among base metal and solder. Sn-Zn solder has extremely low electrode potential than copper base metal, which accelerates the preferential anodic dissolution of zinc resulting in the no dissolution of tin. To suppress the preferential dissolution of zinc is important to improve the wettability of Sn-Zn solder, therefore, the reduction of potential difference between base metal and solder is effective. The addition of silver to Sn-Zn solder and the use of brass base metal was found to be effective by reducing the potential difference between base metal and solder which suppress the anodic dissolution of zinc.
Recently, we have shown that the splat morphology of most metallic materials thermally sprayed strongly depend on the substrate temperature and usually the change occur drastically near the transition temperature ; Tt. In the present study, the effects of substrate material, powder material and PVD coating material on the flattening of the plasma sprayed ceramic particles were investigated. Commercially available several kinds of powders, that is, Al2O3, TiO2 and YSZ, were plasma sprayedand collected on the mirror polished substrate surface. The substrate materials are AISI304stainless steel, brass and glass, and those were held at a designated temperature before spraying. To investigate the effect of wetting on the flattening of the particle, Au, Ti and Al coated substrates by PVD were also prepared. The splat morphology collected on the room temperature substrate was splash type. As the substratetemperature increased, the central solidification area of the splash splat gradually enlarged, and finally the splat morphology changed to the disk type over Tt range. This transitionis maybe caused by both the improvement of wettability at splat/substrate interface and suppression of rapid solidification with the substrate temperature increasing. The different transition behavior was observed on the common substrate material with each PVD coating. It is well known that the standard formation free energy of oxide can be closely related to the static wetting of melt material on the substrate. If this relation can be applicable to thedynamic wetting like thermal sprayed particles on the substrate, it can be estimated from the results obtained that the better wetting promotes the occurence of the disk splat. The observationresults of the bottom surface microstructures of the splats supported well this hypothesis. Consequently, it was clarified that the wetting played an important role on the flattening behavior of the plasma sprayed ceramic particles.
GTA weld metals containing 0.58 mass%W, 1.01 mass%W, 1.47 mass%W and 1.68 mass%W have been prepared, and effects of W on the microstructure, precipitation behaviors, tensile strength and creep rupture strength of the weld metals were studied. X-ray diffraction analyses on extracted residues of the weld metals after PWHT at 1013 K for 2 h revealed the formation of M23C6 and MX type carbo-nitrides. Laves phase precipitated in the weld metals during creep rupture test or aging at 873 K. The addition of W enhanced the precipitation of Laves phase. The chemical analyses of extracted residues showed that the amount of dissolved W in matrix of weld metals after PWHT increased with W content in weld metals. The addition of W improved the tensile strength of weld metals at 293 K and 873 K. The results of chemical analysis suggested that this improvement in the tensile strength was attributable to the solid-solution hardening by W. The creep rupture strength of weld metals at 873 K and 973 K also improved by adding W to weld metals. However, there was little difference between the rupture life of 1.47 mass%W weld metal and that of 1.68 mass%W weld metal longer than roughly 5000 h - 10000 h at 873 K. These results suggest that there is an optimum W content that is most effective in to improving the creep rupture strength. Results of the chemical analyses of residues of aged weld metals suggested that the precipitation of Laves phase was enhanced by the stress or strain during the creep rupture test.
This study was carried out to know the laser weldability of Ni-base superalloy, Inconel 718. Inconel 718 whose thickness and grain size were 2 mm and 84 μm were prepared for a bead on plate test using CO2 laser welding with a power of 1 to 3 kW and with a traveling speed of 0.5 to 5 m/min. The testing plate was solution heat-treated at the temperature of 1340 K for 3.6 ks before welding. The shape of penetration depended on traveling speed and was typically classified into two types of Type C and Type N by specialized shape. Type C had low depth to width ratio like a champagne glass and Type N had high depth to width ratio like a nail head. Type C and Type N weld beads are seen at a side of low welding speed and at a high welding speed side, respectively and the critical welding speed between Type C and Type N is 1.5 m/min in the present study. Liquation cracks easily occurred at HAZ in the case of nail head like penetration. We used a radius of curvature of fusion boundary at neck zone of penetration to represent a feature of penetration. It can be seen that a critical radius of curvature exists by which whether cracks occur or not in HAZ can be judged. No weld cracks were found when the radius of curvature exceeded the critical value of ρcr. Furthermore, as a countermeasure welding cracks can be prevented by increasing the laser heat input over the valus of 100 kJ/m in the present study. According to observation of grain boundary liquation at HAZ, liquation crack was related to grain boundary liquation.
This study was carried out quantitatively to evaluate the hot cracking susceptibilities of various Ni-base superalloys and the effect of grain size on hot cracking susceptibility during laser welding. Ni-base superalloys used were Inconel 718, Inconel X-750, Inconel 617, Inconel 625, Nimonic 90 Waspaloy, Hastelloy X. The grain size of Inconel 718 varied from about 10 to 110 μm. In this study, the hot craking susceptibility was evaluated by a modified U-type hot cracking tester during CO2 laser welding. Samples were solution heat-treated before welding and welded with laser powers of 3 and 5 kW and with a traveling speed of 0.5 to 3 m/min. The hot cracking occurring in the weldment during the bead on plate test was reproduced on the U-type hot cracking test. Consequently, the liquation cracking susceptibilities of various Ni-base superalloys decreased in the order of Waspaloy, Inconel 617, Inconel 718, Hastelloy X, Inonel 625, Inconel X-750 and Nimonic 90. Liquation cracking susceptibility of Inconel 718 increased with an increase in grain size.
Production mechanism for out-of-plane deformation (longitudinal bending deformation and angular distortion) was investigated. The shape of longitudinal bending deformation was determined by the relative position of the neutral axis for the cross section of the object in fillet welding and the welding heat source. That is, when the neutral axis is above the welding heat source, the shape becomes a convex, and when the neutral axis is below the welding heat source, the shape becomes a concave. However, even if the position of the neutral axis, which was determined only from cross section of the object, and the position of the welding heat source coincided, the small longitudinal bending deformation was produced because the central position to expansion and shrinkage did not coincide with the neutral axis of the object. The magnitude of deformation was influenced by the web height and the distance from the neutral axis to the heat source. In angular distortion, the shape of the deformation was determined from the relative position of the neutral axis for the cross section of the flange and the welding heat source. The magnitude of deformation was influenced by the flange thickness, the welding sequence and the welding speed. The generality of the production mechanism for the out-of-plane deformation generated in the fillet welding was confirmed.
In this study, a new method to control the welding distortion of fillet welds which is especially substantial in thin aluminum alloy was proposed. This is the method to effectively reduce the angular distortion during the welding process, which is conducted by TIG heating on the back surface of welding plate going ahead of MIG welding arc. The advantage of this method was experimentally demonstrated, because it was confirmed that the angular distortion could be completely reduced by this method in comparison with the TIG heating applied before and after welding. By using a thermo-elastic-plastic FEM, the main effect of the TIG heating preceding to MIG welding on the decrease of angular distortion was analyzed. Consequently, the large reduction of angular distortion by this method resulted from the two main effects. One effect is that the TIG heating on back surface provides reverse angular distortion by thermal strain. Another one is the preheating effect, which is provided as a result of pre-set temperature distribution of the plate in thickness direction by the TIG heating and the following MIG welding. Accordingly, the decrease of angular distortion sensitively depends on the condition of TIG heating, such as the distance from MIG to TIG torch, the TIG heat input and the width of TIG heat source. In order to maintain the reduction effect stably, keeping a distance to some extent between TIG and MIG torch is more effective. But, it is necessary to select appropriate TIG heat input.
Impact characteristics of diffusion bonded joints of spheroidal graphite cast irons are affected by the graphite particles precipitated on the bond interface during ferritizing. This process is performed to improve the bond impact characteristics after bonding. To improve the toughness of the joints, it is necessary to decrease the graphites. Generally speaking, the graphites precipitate on bond interface, ferrite grain boundaries and nodular graphites in the base metal during ferritizing. Therefore, it is considered that the graphites precipitated during ferritizing are decreased by increasing of the nodular graphites in the base metal. So, diffusion bondings of spheroidal graphite cast irons having four grades of nodule count were performed. Effects of the nodule count of the cast irons and an insert metal on the bond impact characteristics have been studied. Main results obtained are as follows; (1) When the cast irons had a nodule count of 180/mm2 and were bonded without an insert metal at 820°C for 1.8 ks, the ratio of the absorbed energy of the joints to that of the base metals (absorbed energy ratio) was less than 30%. On the other hand, when the cast irons had a nodule count of 249/mm2 or 313/mm2 and were bonded at 900°C for 1.8 ks, the absorbed energy ratios were more than 57% and these were nearly the ratios of the absorbed energy specified in JIS to that of the base metals. (2) When the cast irons had a nodule count more than 180/mm2 and were bonded with an insert metal of 10-μm thick Ni foil at 900°C and 950°C, their absorbed energy ratios were about 100%. (3) When the cast irons had a nodule count of 64/mm2 or 313/mm2 and were bonded at 820°C, their absorbed energy ratios increased with an increase of the thickness of Ni foil as an insert metal and that was reached to 100% when 50-μm thick Ni foil was used as an insert metal. (4) The area of graphite particles that precipitated on the bond interface during ferritizing decreased with an increase of the nodule count of the cast irons. This phenomenon became clear after using a simple model. Since graphite particles on the bond interface are precipitated by decomposition of pearlite during ferritizing, the more the nodule count of the cast irons, the less the graphites.
Fatigue property of the fillet lap joint using arc welding is lower than that of as-received material, which is affected by the various factors such as the stress concentration on the toe due to its own shape and the residual stress retained as tension in the vicinity of the toe. The TIG arc was applied to the local heat treatment in the vicinity of the welded joint parallel to the bead after the MAG welding for sheet steels. The effects of the distance from the bead and the speed of TIG torch on the residual stress perpendicular to the bead were investigated in case of the 310 to 590 MPa class hot rolled steel sheets. This heat treatment in the condition of the distance, 15 mm, and the torch speed, 150 cm/min., changed the residual stress perpendicular to the bead in the vicinity of the toe from tension to zero. As the result, the fatigue strength of the fillet lap joint in the out-of-plane bending mode for each material successfully increased and the improvement in the fatigue strength incresed with increase of the strength of material. The endurance limit for the specimen without residual stress was estimated using the modified Goodman's diagram. The mechanism of the improvement in the fatigue strength by this heat treatment is discussed in view of the release of the residual stress induced by the arc welding.
This report considers the low melting point Au-Sn microsoldering (utilizing the Au 10 mass %-Sn eutectic ; melting point/ 490 K, bonding heat tool temperature/523 K and bonding time/5 s) which is applied to the 400-600 pin count and 0.10-0.15 mm lead pitch connection with 0.018 mmt thin copper lead. This method is performed by heat and press tool gang bonding of tin electroplated (3.5, μ mthick) copper pattern on substrate and gold electroplated (0.5, μm thick) thin copper lead with non flux in air. Au-Sn microsoldered layer has the high peel strength and has the high reliability in 218 K×30 min-423 K×30 min temperature cycle test and 423 K storage test in air that is higher than 37 mass % Pb-Sn microsoldering. As a result of this reserch, it is determined that the low melting point Au-Sn microsoldering is an excellent method for thin copper lead micro connection to the copper pattern routed substrate and the board.