The mechanism of adhesion of the plasma jet-sprayed Ni, Cr, Mo, Ta and W coatings to the Al and mild steel substrates is in vestigated. The compositions of the boundary layer between the coating and the substrate are made clear by application of the X-ray diffraction analysis. Moreover, in order to appreciate in detail the adhesive mechanism and the composition of the boundary layer, an experiment on the behavior of bonding between the substrate and Ni drop heated by the levitation melting process is also carried out. Main results of the experiment are summarized as follows: (1) The substrate surface is melted by the spraying particles, and a boundary layer is formed between the coating and the substrate. (2) The layer consists of an intermetallic compound formed by each element of the coating and the substrate. (3) The layer is important for the sprayed coating to improve the adhesion to the substrate. (4) The mechanism of adhesion of the sprayed coating deposited to the substrate surface and the composition of the boundary layer are made clear from the results of the experiment by the levitation melting process.
In this report we studied the effect of stress pulsation on resistance to stress corrosion cracking of AISI304 stainless steel in the boiling soultion of 42 % MgCl2 under partial pulsating sine wave load. The experimental time to failure of stress corrosion cracking test was compared with the estimated time to failure calculated according to the static linear damage law, in which the time to failure was given as the accumulation of only static damage. The in fluence of the variation of stress amplitude on the life is larger for the case in which the mean stress is low than for the case of the mean stress being high. Moreover, when the stress amplitude is comparatively small (within about 4 kg/mm2), the estimated time to failure teq calculated according to the static linear damage law almost coincides with the experimental value and so the static linear damage law is applicable. When the minimum stress σmin in the sine wave load is larger than the threshold stress of static stress corrosion cracking, the time to failure can be estimated by the time to failure of the static stress corrosion cracking test at the stress σmin and the stress variation ratio. The threshold stress of streess corrosion cracking which is important from the viewpoint of design is also varied by the change of stress amplitude. When the threshold stress under the pulsating stress is expressed by the equivalent static stress, it almost coincides with the threshold stress under static stress.
In previous reports, the fundamental mechanism of penetration, and the influence of some welding conditions and elecrtical conductivity of fused flux on the penetration of base metal are described. In this paper, the melting speed of wire is discussed from the experimental data. The experimental results are as follows. Under the constant welding voltage, the welding current and the steeping length of wire increases as the wire feed speed is increased (See Fig. 1 and 3). When the welding voltage is increased, the wire feed speed should be decreased to maintain the constant welding current, and the steeping length of wire decreases (Fig. 2). For flux III, which has good electrical conductivitiy only at higher temperature compared to flux II, the wire feed speed is increased compared to the flux II under the given welding voltage and current and the wire steeping of the former is a little deeper than that of the latter. The reason is that the heat energy in a molten slag pool of flux III concentrates remarkably at wire tip which is already mentioned in previous report (See report 3). The input energy to the wire is estimated from the melting speed assuming the temperature of molten wire to be 1700°C, and the energy is expressed in the form of equivalent voltage. The resistance drop along the wire is also estimated approximately. These are calculated as shown in Fig. 7. The difference of above two voltages gives the equivalent voltage in heating effect of slag on the wire. From Fig. 7 the equivalent voltage is about 2.3V for flux I (Vt=18V), 6.8V for flux II (Vt=36V) and 8.1V for flux III (Vt=36V). It is interesting that the values remain almost constant independently of the current, When the slag depth is increased, both the wire melting speed and the equivalent voltage increase. This is due to the increase of steeping surface area of wire in spite of the falling down slag temperature. When the root gap is decreased wire melting speed decreases under the given welding voltage, current and slag depth. We presume that the reason is due to both falling down of the average temperature of slag pool increase of welding speed and the low heat of slag at the upper zone due to difficulty of convection.
In the previous report, an experimental study of the molding properties of fiber glass reinforced polyethylene was described. The present report explains the weldability of fiber glass reinforced polyethylene by ultrasonic welding. Fiber glass reinforced polyethylene used for experimental study had a low density polyethylene as the matrix, random mat of glass fiber as reinforcing agent. Ultrasonic welder used for this experiment was made by Seidenshiya-Denshi-Kogyo Co. Ltd., its frequency being 20 KHz and power 1000W. Ultrasonic welding seems to be made in the following way. Bonding surfaces of the to plastics were placed close to each other to the extent of bonding free among polymer being influencial by heat softening melt phenomena caused by ultrasonic vibration of plastics. That is to say, ultrasonic heating effect is considered to be initiated both by heat, due to internal strain caused by compressive vibration, and by crashing effect, due to heat only near the bonding surface caused by the strong stress of surface introduced by crashing between the little gap of bonding surface. We continued the experiment under the assumption that polyethlene bonding at the fiber glass reinforced polyethlene boundary surface proceed by heat from the inner parts of plastics caused by ultrasonic vibration and by heat of the surface, and that the caolscence is made in accordance with the progress of mutual diffusion of glass fiber caused by static load. The following summary can be made from the results of the present experiment. Ultrasonic welding produced good results when glass content was small. Good weld had nearly the same strength of fiber glass reinforced polyethylene base material, by the mutual diffusion of glass fiber.
Continuing study was made on the effect of alloying elements on brttle fracture characteristics of submerged-arc welded joint. Small amount of titanium is strongly effective improving the weld bond fracture characteristics. A favorable effect of titanium could be clearly recogrized in a static bend test of Vee-notched Charpy specimen, thus showing the strain rate dependency of this phenomenon. And the favorable effect of titanium was also recognized in lower nitrogen steel. Favorable effect of titanium is presumed to be due to the formation of titanium nitride, decrease of free nitrogen and increase of hardness in the weld heat-affected zone. This was also concluded from the results of chemical analyses of aluminium, titanium and nitrogen in acid-soluble and insoluble state and that of nitrogen as aluminium nitride in the duplicated weld heat-affected zone. A suitable composition of high tensile steel for high heat input welding is proposed based on the aobve experimental results.
Grain growth in weld-heat affected zone has a detrimental effect on the properties of welded joint. Therefore, the authors tried to investigate grain growth during weld thermal cycles systematically. In this report, it is intended to estimate grain growth during thermal cycles quantitatively using data of grain growth during isothermal heating. From the experiment of isothermal heating on the grain growth of commercial-purity nickel, deoxidized copper and commercial-purity aluminum, it was confirmed that equation (2) is suitable as the isothermal grain growth equation. The values of constants in this equation were obtained from the data of isothermal heating. To determine grain size during weld thermal cycles, the following method was adopted. Namely, weld thermal cycles were divided into small steps by Δt and the isothermal grain growth equation (2) was applied to each step. By piling up grain growth on these steps, grain size at temperature Ti during weld thermal cycle was represented by the equation (6) or (7). Weld thermal cycles were applied on commercial-purity nickel, deoxidized copper and commercial-purity aluminum. Grain size was measured on the specimens quenched from various temperatures during applied thermal cycles. Measured grain size was compared with the one calculated using the above mentioned method, i.e. the equation (6) or (7). Accorhing to the result, measured value fairly well corresponds with calculated value. Consequently, it is considered that, in the materials of commercial purity, grain size after any thermal cycle can be calculated using the above mentioned method. Therefore, this method is useful to estimate grain growth in weld-heat affected zone.
A few reports have been made on the influence of electromagnetic stirring on weld zone, from the point of minimization of crystal grain and acceleration of blowhole decrease, in the case of TIG and MIG welding for titanium alloy or aluminium alloy. But the application for Submerged-arc welding has not been experimented. Therefore, in the former report, the authors investigated, how the electromagnetic stirring made influence on its bead shape, penetration and solidification structure of D.C.submerged-arc welding of mild steel. From this study the authors made it clear that the shape of penetration showed very peculiar change and that the primary crystals of weld metal were minimized. In this cotinuous report, the authors investigted how electromagnetic stirring hardness distribution and notch toughness of Submerge-arcd weld zone changed. The authors measured the hardness distribution by micro-Vickers Hardness tester, and the notch toughness by V-notch Charpy impact test. From these studies the authors have found out the following results. 1) The hardness increases by electromagnetic stirring. 2) As to the notch toughness, the authors made the transition curves of absorbed energy and fracture phase from the impact test, and from them, obtained the transition temperature of both 15ft-lb and fracture phase. As the result it became clear that both of the transition temperatures moved to the lower temperature side by 20 degrees C. The author also made the micro observation of fracture phases of impact test pieces with electron microscope and considered the changes of shape of the destructive phase caused by electromagentic stirring.