In this study, the influence of brazing process conditions on the Ni brazed joint (Ni-Cr-B) strength of SUS304 stainless steel has been investigated by the tensile test, microscopy, EPMA and SEM. The effects of the brazing clearance, the brazing temparature, and the holding time at brazing temperature are described. The tensile test results show that the Ni brazed joint strength of SUS304 is found to depend on the brazing clearance and the brazing temperature. The results obtained are as follows ; (1) The brazed joint strength depends on the brazing clearance and its maximum strength is obtained at the brazing clearance of 20μm. (2) In the metallographical analysis, it is observed that considerable amount of Ni rich fragments concentrate at the central line zone of the brazing layer. The mass of Ni element may correspond to the original brazing alloy. At the clearance more than 50 μm, the segregation (B-Cr) can be observed at the central line zone of the brazing layer. (3) The brazed joint strength depends on the brazing temperature and its minimum strength is obtained at the brazing process temperature 1380 K with the brazing temperature holding time of 600 sec. This temperature (1380 K) fosters the segregation (B-Cr) of the brazing alloy and the joint strength is related to its segregation size.
The effect of ambient gas and pressure on the penetration and plasma behavior for AISI 304 stainless steel in CW CO2 laser welding with 4 kW output power was investigated. The major results are summarized as follows ; (1) The penetration depth significantly increased by reducing the ambient pressure. At the same time, the quantity of the laser-induced plasma also decreased as the ambient pressure decreased. The plasma in He and N2 ambient completely disappeared under the pressure of less than 100 torr, resulting in the significant increase in the penetration depth. The penetration depth reached more than 12 mm under the pressure of less than 100 torr at the traveling speed of 25 cm/min, which was around twice as deep as that under the atmospheric pressure. It was mainly because the formation of plasma which blocked the laser beam entering to the workpiece was greatly suppressed under the low pressure. (2) The plasma generation was dependent upon the physical properties of gas element as well as the ambient pressure. The higher the ionization potential and heat conductivity of the gas element was, the larger the plasma became.
An experimental test of the new welding system, High Frequency Preheating plus Plasma (High Plasma), was carried out in the commercial line to make SUS304 welded tube of 60, 5 mm outside diameter, 3 mm wall thichness. A high frequency induction coil and an impeder assembly were set up in the preceding position of a plasma torch which is located between pairs of squeeze roll. An available speed of the High Plasma could be at least doubled by preheating at the temperature of 723 to 773 K (450 to 500°C), and also accompanied the satisfactory weld quality as well as small electric power consumption of High Frequency preheating.
Copper and some other materials were joined using the resistance heating apparatus by which heating and pressure could be applied simultaneously. The materials used were presoldered and the alloyed layer was formed on each of them by using Pb-Sn solder. Tensile test at the room temperature revealed that fracture of all specimens originated in copper material. The layers consisted mainly of Cu-Sn, Cu-Zn-Sn, Cu-Ni-Sn, Cu-Fe-Ni-Sn when copper, brass, nickel, and Fe-42Ni alloys were jointed with copper respectively.
The low frequency pulsed MIG welding process of new current waveform control to switch over unit pulse conditions (pulse current, pulse duration) in the fixed cycle was developed and its effect were investigated for aluminium and its alloy. By using this new welding process, the bead appearance having clear ripple pattern, such as TIG welding bead can be obtained and the gap tolerance of lap and butt welding joint can be expanded.
Photoluminescence spectroscopy of the plasma induced by the continuous CO2 laser was observed in the range of wavelength 190-400 nm. From the results of the spectrum analyses of the plasma, the plasma temperature was measured and its formation mechanism was discussed. It was found that the plasma consisted of rich emission lines of excited and ionized metallic elements. The intensity of atomic emission lines from the plasma was dependent upon the physical properties of the gas element such as ionization potential and heat conductivity. The plasma temperature estimated by a line intensity ratio method was 13000-14000 K irrespectively of the kind of shielding gas element. Critical power density of CO2 laser for maitaining the plasma was about 5×105 W/cm2.
In diffusion bonding of Ti alloy to stainless steel, brittle intermetallic compounds are formed at the bond interface, therefore strength of the joints obtained by a conventional technique were extremely low. In this research, possibility to obtain high strength joints preventing the formation of intermetallic rmmnnunds by diffusion bonding in a short time were examined experimentally. As the results of the experiments, it was clarified that high strength joints of Ti alloy to stainless steel were obtained by diffusion bonding in a short time (for example, 60 s at 1023 K) of the cleaned specimens by ion bombardment with fine surface roughness.
The dynamics of bridging transfer are theoretically and experimentally investigated. Timedependent deformation of the liquid metal bridge, which.is formed between the electrode and the pool by a contact of a pendent drop with the pool surface, is observed by high speed photography and simulated with aids of the numerical solution technique for the dynamics of a viscous incompressible fluid with a free surface (MAC method) based on Finite-Difference Method. It is shown that the liquid of the pendent drop is driven to flow into the pool by the capillary force and the electromagnetic pinch force acting on the conducting bridge.
Temperature distribution in edge cooled ZnSe lens was numerically analyzed during focusing high power CO2 laser beam where thermal conductivity K varies with temperature T, K=K(T). Simple analytical solutions at steady state were also derived for different laser modes assuming K is constant. Results obtained are summarized as follows ; 1) Assuming K=const, the accuracy of calculated temperature decreases with increasing steady temperature at the center, TSC, which becomes 1.5 times as high as the exact value at TSC=100 C. (2) Steady temperature gradient calculated with K=const is proportional to r in laser irradiation region for a circular uniform beam of radius a, and is given by a curve having a peak at r= 1.12a for Gaussian beam (a=1/e-radius), of whidh peak is 64% of that of the circular beam. (3) Simple equations to provide accurate steady temperature distribution and gradient were derived ; TK (r) =T (r) / (1-mTsc) and (dT/dr)K = (dT/dr) / (1-mTSC), where T (r), TSC and dT/dr are temperatures at r=r and r=0 and temperature gradient at steady state for K=const, respectively. (4) The temperature rise of ZnSe lens was measured during focusing CO2 laser beam by a fluoroptic thermometry, and was found to agree well with calculated values.
As shown in the previous papers, not only high deposition rate but also low oxygen weld metal without any defects could be obtained by the AC-MIG welding process. To clarify the effect of oxygen content on the mechanical properties, regression analysys of the weld metal toughness, thermal analysys of the transformation during welding and examination of the oxide inclusion have been conducted in this study. Main results are as follows. Good correlation between the vTrs, the oxygen content and the tensile strength was existed. And the vTrs became lower than -90°C at the optimized oxygen content of 150 ppm and the tensile strength of 65-70 Kgf/mm2. There was a suitable transformation temperature and its range for the toughness. This meant high toughness could be achieved by the homogeneous fine acicular ferrite structure transformed intra- and interganulary at a certain temperature simultaneously. Fine oxide particles contained Ti at higher oxygen content than 120 ppm, and fine acicular ferrites were nucleated.
In the previous papers , authors clarified that the crack generation time, the crack length and the crack propagation speed can be detected by the strain information obtained from a strain gauge bonded on the indentation surface, in the case of single spot-welded joint specimens of tensile-shear type. Thereupon, by developing further this technique, authors have tried to estimate or detect in process the crack generation time, the crack depth, the fatigue life, etc. in the multi-spot-welded structure, when the direction of the main load axis and/or the load type which act in each spot weld are unknown. For this purpose, authors developed a new type strain gauge (Authors call it "SA-gauge"). This SA-gauge has a special gauge pattern in which eight sectorial gauge elements are radially arranged at angle intervals of 45°, and can be bonded on the indentation surface of nearly 5 mm in diameter. In this paper, the specifications of SA-gauge and the basic experiment results obtained are described as the first step of a research for the prediction method of the fatigue strength and/or life of multi-spot-welded structure using SA-gauge. The specimen material used is mild steel sheet of 0.8 mm in thickness. The test specimens used are three types of single spot-welded joint specimen of tensileshear type, cross-tension type and L-tension type.
X-ray study was made on deformation layer of aluminum alloy A5083 of cutting surface using water jet. Distributions of plastic strain in the deformation layer of the specimen were estimated using integral breadths of X-ray diffraction intensity curves. Two methods were used. The first method is to obtain the intensity curves every time when the tnin layer of the specimen is chemically polished using 20% NaOH+80% water at 70°C. The other is to use the phenomenon that the penetration depth of X-ray depends on the diffraction planes. Almost the same distributions were obtained in both methods. Plastic strain in the deformation layer decreased exponentially. Plastic strain on the cutting surface increased slightly with increasing water pressure and cutting speed and was between 15 and 44%. The thickness of the deformation layer was between 0.15 and 0.19 mm.
Various methods of surface treatment have been performed for improving the properties of metals and alloys. Among these surface treatment, the flame sprayed coating technique is selected, since this technique is expected to be one of the effective methods for the surface treatment. The flame spraying used for this experiment has low cost equipment and easy maintenance, and can be adopted in various places and forms. In this paper, the fatigue strength of the high strength steel (HT 60) is examined by the sprayed specimens with four kinds of thermal spray materials (Zn, Al, ceramics and metallizing alloy). The results are as follows: 1) The surfaces of the turning and blasted specimens have a little higher hardness due to the work hardening effect. 2) The fatigue limit of the rotate-bending fatigue test is the same as that of the blasted specimen, and it has no relation to the blasted specimen and the kinds of spray material except the metallizing alloy material. 3) The microstructure of the base metal near the sprayed coating is the mixture of ferrite and pearlite. 4) The micrography of the fatigue fracture surface shows mainly dimple and quasi-striation pattern.
Effects of specimen sizes and loading types on an interfacial strength of bonded dissimilar materials were investigated. The energy release rate, g, was used for estimating the strength. Resin and steel were used for the dissimilar materials. The Implant type specimens were tested under both tension and torsion loading types. g-value was calculated by the finite element method (FEM). The larger the diameter of the specimen is, the lower tensile and/or torsional strengthes is, in each loading type. However, as g-value almost shows constant value in each loading type, g-value becomes useful parameter for estimating an interfacial strength of the joint bonded dissimilar materials.
Friction welded butt joints have come into wider use as structural members and machine elements such as propellor shaft and engine value of automobile structure, cutting tool, motor shaft and so forth. Friction welded butt joints have opposite aspects in their mechanical properties : Low absorbed energy in Charpy impact test and high joint efficiency under both monotonic tensile and fatigue load conditions. Furthermore, recent study on the fracture toughness of the joint revealed that the joint possessed sufficiently high toughness value for practical applications despite of its low Charpy impact energy. But, it is also clarified that the scatter of fatigue distribution of the joint is larger than that of the parent material. Therefore, it is an important problem to clarify main factors controlling the fatigue strength and fatigue life distribution from the viewpoint of reliability design engineering. And, the corrosion fatigue behavior of the joint is also an urgent problem to be solved, because some of the joint elements are practically used in corrosive environments. In order to clarify the corrosion fatigue behavior of the friction welded butt joint composed of similar carbon steel, JIS S25C/JIS S25C, a series of rotating bending fatigue tests was carried out in ordinary atmospheric environment and in artificial seawater. Results of the study indicated that the fatigue strength of the joint at 107 stress cycles in artificial seawater was almost the same as that of the base material, and the evaluation of fatigue life distribution on Weibull probability paper showed that, in artificial seawater, the scatter of fatigue life distribution for the joint is smaller that that for the base metal. Above mentioned corrosion fatigue characteristics of the joint can be discussed reasonably on the bases of the corrosion pits generated on the notch root area of the joint specimen.
In this paper, closure measurement of short fatigue crack by surface wave technique of ultrasonic testing is recommended. Surface wave could be good for measuring a closure of short crack, because surface wave has it's 75% energy within the region of 40% of it's wave-length from a surface. To detect a short fatigue crack and to measure the closure of short crack, both the surface wave method and the strain compliance method was used. Crack initiation was detected earlier by the surface wave method than the strain compliance method. The relation between crack growth rate da/dN and effective stress intensity factor range ΔAeff, obtained from the surface wave method showed a good agreement with those obtained from the strain compliance method.
Aluminum metal matrix composite welds have been produced by non-transferred plasma arc spraying of aluminum alloy powder containing SiC (Osprey powder). Almost no Al4C3 phase was observed in the sprayed deposit. However, the deposit contained excess soluble silicon because of pyrolysis of some SiC particulates. Heat treatment after spraying tends to improve the strength significantly, possibly by enhancing the bond between the substrate and the deposit and/or by improving the bonding between the particulates and the aluminum matrix, as well as by improving the deposit matrix itself. Hot isostatic pressing of the samples to eliminate porosity had only a small effect on the final strength of the joint.