The relationship between the morphology of Au, Cu and Ag metal targets and the formation of droplets on the metal thin films was investigated using the Pulsed Laser Deposition (PLD). The metal thin films were made from the metal targets by irradiating KrF excimer laser at various laser fluences from 2. 5 J/cm2 to 10 J/cm2 in a vacuum chamber. The surface morphology of the target after laser irradiation was observed by a Scanning Electron Microscope (SEM). It was found that spouting holes occurred on the surface of the Cu target after laser irradiation at the laser fluence of 10 J/cm2. Droplets of about 1 (m in diameter were found around the spouting holes. Oxygen, Phosphor and Sulphur were detected at the spouting holes from Energy Dispersive X-Ray (EDX) analyses. However, at the laser fluence of 2. 5 J/cm2 spouting holes were not found. The observation on the surface of metal thin film indicates that particles of about 1 μm in diameter fly out away from the target and then reach on the surface of substrate with high velocity as droplets. The same phenomenon was observed when Ag and Au targets were used. In the case where a high purity of Cu (111) single crystal target was used, it was obvious that the surface morphology of the target after laser irradiation would be good enough at the central zone subjected to the laser irradiation of higher laser energy than at the circumference zone.
In recent years, applications of solid-state lasers with frequency conversion techniques such as SHG, THG and FHG to precision microfabrication progress rapidly. When nonlinear optical crystal used for frequency conversion absorbs laser beam, temperature of the crystal rises, and the frequency-conversion efficiency decreases. In this study, KH2PO4, that is potassium dihydrogen phosphate (KDP), whose physical properties are well known was supposed as a nonlinear optical crystal for SHG. Temperature dependence of frequency-conversion efficiency was examined theoretically by solving the coupling problem composed of heat conduction equation and complex amplitude equations, which are derived considering the absorption of laser in the crystal. The temperature change of the crystal induced by Nd:YAG laser absorption, the local change of refractive indices, and the consequential variation of SHG frequency-conversion efficiency were analyzed for single and repetitive pulses. As a result, the temperature dependence of frequency-conversion became clear quantitatively. Remarkable inverse-conversion of SHG also appears for the repeated laser irradiation with high power density.
As a feasible welding method in space, the authors have proposed the Space GHTA (Gas Hollow Tungsten Arc) welding method in the previous papers. The Space GHTA welding using the high frequency power source may have an electro-magnetic noise problems of computer equipments placed on the ISS. In this report, the Space GHTA welding experiment using the DC high voltage power source was carried out in the ISS orbital pressure 10—5 Pa. The results are summarized as follows, 1) It is made clear that there is a shifting phenomenon in which a glow or an arc is formed after the spark at starting phenomenon of the Space GHTA welding in high vacuum condition, and the feature of those starting phenomenon are demonstrated. 2) The arc ignition unit of GHTA by DC high voltage power source can be used in the ISS orbital pressure. 3) The arc formation ratio increases with increasing the stating voltage, but the starting current has no effect on the arc formation ratio. 4) The arc formation ratio increases in order of arc operating gas Ne, Ar and Kr under the same starting conditions.
Manual TIG arc welding method is a difficult operation for skill working, because it is necessary to operate adjusting heat source and adding filler rod in getting on well with molten condition of the base metal. Accordingly, a semi-automatic TIG welding method becomes valid for a settlement to this problem. Because, in this process, suitable welding procedures and welding conditions are unknown, so in this paper,these matter are investigated. Main results are as follows ; 1) Suitable wire feeding conditions are obtained to adjust continuous transfer of wire molten metal. In this case, the favorable wire feeding position is at the tip end of molten pool. 2) Wire feeding angle has a impact to the formation of penetration bead in one-side welding. In overhead position welding, the fine convex penetration bead can be formed with about 45 degree of wire feeding angle. 3) The semi-automatic TIG welding system in which a wire feeding nozzle is separated from welding torch is favorable, because it is capable of changing wire feeding position and intermitting of welding operation.
First, five items are mentioned as the main problems that have complicated the workability of hot wire TIG welding. In this paper, it is shown that two fundamental items in the problems have been examined and their countermeasures have been established. Regarding the problem of magnetic arc blow by the wire current, it is effective to use a pulsed current for wire heating. It is possible to reduce the influence of magnetic arc blow by keeping a sufficient non-pulse period of the wire current because the arc is not blown during the non-pulse period. Regarding the problem of arcing from the hot wire, a countermeasure in which the wire current is not supplied when the wire tip is detached from the base metal has been established. From the wire voltage during the non-pulse period of the wire current, it can be easily detected whether the wire tip is separated from the base metal. The application of these developed technologies makes it practical to perform semi-automatic TIG welding with a hot wire torch and an arc torch in each hand.
The structure of Si3N4/SUS304 joints using a Cu-Ti type active-metal brazing material is discussed. As a Cu-Ti brazing metal makes a small fillet on Si3N4/SUS304 bonding, the edge structure of the copper interlayer is very important for reducing residual stress. Cone-shaped Si3N4 was applied in the present study, with the aim of suppressing local stress generated by the unequal distribution of brazing metals. A suitable thickness for the copper interlayer, as well as specifications for taper and slit formation at the interlayer edge, were determined based on stress analysis and bonding strength evaluation. Those findings led to a great improvement in the tensile test results for the joint, and the tested design proved effective in a Si3N4/SUS304 joint, providing decreased residual stress and increased reliability in the bonded seal parts.
Friction welding of aluminum alloys to copper was carried out in order to examine the weldability with particular reference to the effect of the intermetallic formation at the weld interface. The maximum joint efficiencies of A1050, 5000 and 6000 series alloys to copper were more than 80 %, while those of 2000 series and A7075 alloys joints were less than 50 % and scattered widely. For joints of A2024 and 5000 series alloys which contain rather high magnesium content, intermetallic compounds of Al-Cu-Mg system were formed at the weld interface in addition to that of Al-Cu system. In the other joints, only intermetallic compounds of Al-Cu system were formed. A mixing layer, in which pieces of copper and intermetallic compounds were incorporated into aluminum alloy, was formed near the weld interface. The mixing was very intense, in the joints with low efficiency, namely joints of A2011, A2024 and A7075 to copper, and these joints were fractured in this mixing layer and at the weld interface. On the other hand, the joints with high efficiency, namely joints of A5052 and A6061 to copper, had thin and even mixing layer. The mixing layers observed in the joints of A1050, A2017, A5056 and A6063 to copper were thinner than those of the other joints.
Laser welding is increasingly employed as an effective method to join small areas of parts with small distortions. Distortions of micrometer or sub-micrometer level generated after joining automobile parts are treated over laser welding, which is a process with small distortions. In this study, a general-purpose method, which decreases distortions without special processes before/after welding, is discussed. Consideration based on fundamental experiments and theoretical analyses is presented in order to understand a deformation behavior during a welding process, and to employ a technology into actual production lines. This paper deals with experimental methods and theoretical analyses about bending deformations in joining cylindrical parts by circumferential welding. Transition of bending deformations is discussed in order to control a residual deformation. A new method to control a distortion from results of the distortion behavior analysis is proposed to be employed into a production line.
It has been greatly interested that the development of a new high strength steel with grain refinement. Fine grain steel has the same component and the weldability as a mild steel, whereas conventional high strength steel has a low weldability due to its alloying elements. It is found the occurrence of softening caused by coarsening in the heat-affected-zone (HAZ) of weld parts of the fine grain steels and mechanical design of weld parts including weld HAZ softening becomes much important. In this paper, the production of an ultra-fine grain steel (NFG steel) produced by high reduction and high cooling rate is firstly introduced. Mechanical properties of the weld part is examined by considering the characteristics of tensile strength under the theory of the strength of the undermatched joints. The effects of the mechanical and geometrical heterogeneity on tensile strength of the HAZ softening joint are studied by using the large-deformation finite-element analysis. It is found that a design of the HAZ softening joint is possible considering welding conditions and tensile strength of the joint mostly overreach that of the base metal.
It has well known that mechanical and geometrical heterogeneity are naturally contained in weld parts. Development of the production on fine grained steel that has high strength by refining the grain size has recently become active, but the fine grain size is coarsened and its heat-affected-zone (HAZ) is softened by weld heat input. The heterogeneity in welds is affected by the steel compositions and the welding conditions. It is important for actual use and design to know tensile strength of HAZ softening joint with consideration to heterogeneous effect. The predicting equation of tensile strength of the HAZ softening joint with fine grained steel is proposed in this paper. The effects of mechanical and geometrical heterogeneity are considered in the equation, and it is found that the equation precisely predicts tensile strength of the HAZ softening joint.
Deformation behavior and ductile crack initiation in HAZ softening joints by fine grained steel are studied in this paper. Not only deformation but also fracture of heterogeneous material are affected by plastic constraint due to strength mismatch, and are different from those of homogeneous material. Large-deformation finite-element analysis is done in a tensile round-bar specimen with base metal, weld metal and HAZ softening zone, and ductile crack initiation is discussed. Necking initially generates in HAZ for all HAZ softening joints, and HAZ necking usually continues before fracture. There are some cases that the location of necking after proceeding deformation finally shifts from HAZ to weld metal or base metal when the joint is fabricated by high-strength steel with high plastic constraint condition. However, the locations of final necking and fracture initiation do not always correspond. This is because the location of ductile crack initiation is determined from the relation between stress triaxiality and equivalent plastic strain, and they are independent of necking deformation. It is found that the effects of mechanical and geometrical mismatch on tensile strength of HAZ softening joint depend on the behavior of deformation and fracture.
The purpose of this study is to investigate whether experimental results of static fracture strength of lap joint made by laser welding can be predicted by numerical analysis or not. First, numerical analytical method was devised for estimating the experimental result of the relationship between load and displacement of shear test. Next, experimental result of static fracture strength was predicted by using the concept of critical equivalent plastic strain, that the lap joint is fractured when maximum equivalent plastic strain reaches a critical value. The static fracture strength of lap joint was predicted by the concept of critical plastic strain when fracture occurs in the base metal. However, when lap joint was broken by shear fracture in the joint part, shear strength of lap joint could not be predicted by the concept. The shear strength of lap joint could be predicted from the shear strength of weld metal.
Mechanical properties of laser welded ultra-fine grained high strength steel were examined using a 20 kW CO2 laser facility. The welded joints showed good tensile strength as all pieces were broken at the base metal. In CTOD test the critical CTOD value was the lowest at the weld metal. To prevent the fracture path deviation (FPD) in Charpy impact test, we used three-weld test assembly. The results confirmed that reduction in carbon quantity improved the weld metal toughness.
As reported before, there are many dislocations in the martensite matrix due to the mechanism of transformation itself. The actual structure of pipes includes the tensile prestrained part of the outside layer and it has become clear that the outside layer with prestrained HT780 has remarkable deformation behavior even without uniform elongation. The initial amount of uniform elongation must be important in preventing the disappearance of that characteristic after prestraining. Accordingly, in this report several methods of developing steels with higher initial uniform elongation are investigated. 1) By using finer microstructure (γ grain size is more than 9.4), clear uniform elongation is shown even after 3 % prestraining. However, the effect of grain size on the configuration of stress-strain curve is smaller than the effect of ferrite structure. This is presumed to be because one prior γ grain is composed of so many substructures that function as grains, i.e. ; packet or lath. However, from the point of view of the ability of piling-up dislocation, γ grain boundary is superior to the others because γ grain boundary has more differences of crystallographic orientation. 2) By increasing carbon content (more than 0.26 %), uniform elongation can be enhanced through precipitating carbides in laths. However, ordinary HT780 steels for structures where welding is carried out with not more than 0.17 % carbon shows a constant value of uniform elongation. In this carbon range, uniform elongation is controlled only by tempering temperature and independent of chemical composition. According to observation of microstructure, there are few carbide precipitates in laths but many precipitates in the boundary between laths. Therefore, the increase of carbon content does not effectively contribute to enhance the ability of work hardening.
This paper deals with a cutting deformation produced by continuous parallel cutting lines as the basic cutting line for studying the deformation of the unicursal cutting which is applied in the cutting field. Former researches about the cutting deformation had been carried out by cutting one straight line, therefore a basic research on the deformation of plate made in the cutting field exits hardly. The expeiment was done by laser cutting. The cutting deformation was generated by inherent strain, then the distributions of inherent strain were measured by the sequential removal of layers method. It is shown by experimental data of the inherent strain distribution that main factor of cutting deformation is the plate width during cutting process. The predictive equation of cutting deformation made by continuous two parallel cutting lines was proposed using parameter of the average temperature rise.
Electrical Sialon ceramics having TiN were joined with SKS3 metal by using a Ag-Cu-Ti active brazing metal layer having a thickness of 100 μm or 400 μm at 1113 K for 300 s in a vacuum. Residual stress distribution in the ceramics and metal sides was measured by X-ray stress analysis. High residual stress over several hundred MPa was detected in a region up to about 10 mm from the brazed interface in the metal side of brazed joint sample. To reduce the residual stress by plastic deformation of the brazing metal layer, stress relaxation methods such as heat treatment after joining and use of insert metal were applied. These methods were effective to relax the residual stress of σy in the ceramics side (σy : residual stress in vertical direction to the brazed interface). Four-point bending strength of the brazed joint specimen was well related to the peak value of σy in the ceramic side and the average value of σx in the metal side of the brazed joint sample (σx : residual stress in parallel direction to the brazed interface). In the case of high strength brazed joint specimen, the four-point bending strength showed 85 % of the strength of Electrical Sialon at room temperature. The strength decreased with increasing the temperature.
This study aimed to manufacture the environmental correspondence materials with functions of water repellency and antimicrobial activity according to make a surface by the thermal spraying method. For the water repellency characteristic was found on the fluorine-carbon, and the antimicrobial activity was detected by using the CuCl2¤3Cu(OH)2 powders, the thermal spraying coatings were made by the compound wire where two kinds of the powders were added to the aluminum tube. The functions of water repellency and antimicrobial activity were investigated. The results of the experiment show that two kinds of the CuCl2¤3Cu(OH)2 powders were well dispersed and settled. The mean contact angle was 139° tested by the water droplet method, which shows no much different from the contact angle of the coatings made by only the fluorine-carbon filled wire. Furthermore, by adding the CuCl2¤3Cu(OH)2 powders, at the same time as the water repellency characteristic, the remarkable antimicrobial activity was also clarified form the results of the culture experiment basing on the JIS standardization.
Cast iron has been widely used for the parts of sliding wear such as cylinder bores of motor engines. High wear resistance of the cast iron is mainly due to the fine pearlite structure and the existence of graphite, which yield hardness and lubricity, respectively. These features are derived from the rich carbon content (3-4 %). However, under more severe sliding conditions such as those in high-power motor engines or exhaust-gas recycle (EGR) engines, cast iron without any treatment is not sufficient for wear resistance. In this study, the surface modification of cast iron by laser melting was carried out to obtain a higher wear-resistant surface. The surfaces of cast iron samples were melted by a pulsed Nd:YAG laser or a CW Nd:YAG laser. The thermal changing of the laser-processed substrates was analyzed numerically to estimate the cooling rate in solidification. It was showed analytically that cooling rate in solidification is varied by laser condition and that high cooling rate is obtained by pulsed laser. A fine martensite-ledeburite microstructure with hardness of about Hv 1000 was obtained by a pulsed laser. In the pulsed laser melting, not only the cooling rates, but also the differences of the peak temperatures in the cooling phase are important parameters that have effect on the formation of the chilled mirostructure.
The authors have studied on the laser surface modification of cast iron aimed at refining the wear resistance. It was already reported that cooling rate in solidification is varied by laser condition and that a fine martensite-ledeburite microstructure with hardness of about Hv 1000 was obtained by a pulsed laser. In this report, wear characteristics such as wear resistance and scuffing resistance were investigated by performing pin-on-plate sliding tests that demonstrate the friction between a piston ring and a cylinder bore. Surface-modified cast iron samples, especially irradiated by a pulsed laser properly, showed good wear resistance even under severe sliding conditions. The scuffing resistance depended on the countermaterial; CrN coated pins showed the higher scuffing resistance than hard Cr plated pins and nitrided pins.
The present paper describes the relationship between joining phenomena, i.e. the friction stage and the yield strength of substrates of dissimilar friction welding. The materials used were oxygen free copper (OFC), commercially pure titanium (P-Ti), commercially pure aluminum (A1050) and type 7075 aluminum alloy (A7075). The combinations of P-Ti/OFC, A1050/OFC and A7075/OFC were joined by using a conventional friction welding machine. The same friction welding condition was used for all combinations. Main conclusions are obtained as follows. (1) The friction process, i.e. joining behavior, friction torque curve and welded interface behavior was observed different for each joint. The welded interface of P-Ti/OFC joint sparked, and intensively flew from P-Ti substrate. The upsetting (deformation) occurred at only P-Ti side during the friction stage after initial peak torque. The upsetting also occurred at only A1050 and A7075 substrates for A1050/OFC and A7075/OFC joints, respectively. (2) The temperature of each joint during friction welding process was measured at centerline, half radius (1/2R) and periphery portions. The maximum temperature of P-Ti/OFC joint was much higher than those of both A1050/OFC and A7075/OFC joints. The maximum temperature of A1050/OFC joint was almost same as that of A7075/OFC joint after initial torque. (3) In P-Ti/OFC joint, wear and adhesion of surfaces started at periphery portion (outer surface) of OFC substrate, and they extended toward center portion (center axis). Then, the P-Ti substrate adhered to OFC substrates after the weld faying surface of P-Ti substrate became the wear state. In A1050/OFC joint, the wear and the adhesion started at whole surface of A1050 substrate. In A7075/OFC joint, wear and adhesion started at periphery portion of both A7075 and OFC substrates, and they extended toward center portion. (4) It is considered that the joining behavior, friction torque and welding temperature were affected by the relationship between the loaded friction pressure and the yield strength of substrates.