This paper discussed the posibility of selection of optimum welding condition by adopting the estimating equation for welding consisting of some welding behaviours to responce surface method using a 12 mm diameter SUS304 stainless steel. First, by analysing the relation between the welding behaviour and the tensile strength of welded joint using multiple regression analysis, an estimating equation for welding capable to estimate non-destructively was obtained. Next, by setting up the joining evaluation value obtained by the estimating equation for welding as a dependent variable and the welding condition as an independent variable, the optimum welding condition was selected using the responce surface method, namely, the posibility of selection of optimum welding condition without tensile strength was confirmed. The optimum welding condition obtained was the friction pressure P1=30 MPa, the upset pressure P2=170 MPa, the friction time t1=3.5 s and the rotating speed N=2425 rpm, and the joint efficiency was 102% with a satisfaction.
The effects of spary conditions on the properties of HVOF Cr3C2-25%NiCr coatings are investigated using parameters of oxygen flow, fuel gas flow and spray distance based on orthogonal regression experimental design method. The propane gas is used as a fuel gas. The properties of the coatings are characterized by adhesive strength, hardness, abrasive wear and erosion tests. The abrasive wear is estimated using dry-sand rubber wheel tester. The relationships between the properties of the coatings are examined. The results show clearly that the properties of HVOF Cr3C2-25%NiCr coatings are greatly influenced by gas flows of both oxygen and propane during HVOF. The regression formulas with 2nd power between the properties and spray parameters are established. It is found that the optimized coating with good abrasive wear and erosion resistances can be obtained with adequate gas flows of both oxygen and propane. The examination of experimental results showed that there is no evident relation between hardness and wear resistance for HVOF Cr3C2-25%NiCr coatings. On the other hand, it is found that there exist evidently the correlation between coating abrasive wear and erosion wear at low impact angle.
The bonding a copper pipe to an aluminum one was carried out by using eutectic reaction occurred at the faying interface when the copper pipe was inserted into the aluminum one. In order to understand the appropriate bonding conditions, the fracture and removing behavior of the oxide films on the pipe surfaces were investigated in detail. The following results were obtained. The strength and the bonded area of the joint are increased with increasing inserting rate and decreasing bonding temperature. Scraping the copper pipe edge by the solid-state edge of the aluminum one promotes the fracture and removing of the oxide film on the copper pipe surface and leads to the increase of bonding area and strength. At first the oxide film on the copper surface is consisted of copper oxide, however, the retained oxide film in the bonded layer is changed to oxide consisting of about 70% or more aluminum oxide. By making the oxide film on the copper surface thicken before inserting, that is more easily removed and less remained in the bonded layer.
With respect to the blowholes to be formed by the vaporized zinc gas coming into a molten pool through the gap of seams in the consumable electrode type pulsed arc welding of galvanized carbon steel sheets, the means to decrease the number of them by inducing the flow of molten metal along the bottom face of the molten pool has been examined and studied. As the result of the vibration of mother metals by 1 mm while welding so as to produce the back and forth flow of molten metal at the bottom face by the longitudinal vibration of molten pool, the significant reduction of blowholes has been achieved. The optimum frequency of vibration seems to be about scores of frequency (Hz) which can be supposed to be the self vibration frequency to be determined depending on the size of molten pool, physical properties of type of molten metal, etc. In order to obtain the same effect as the above by the control of electric current, by minimizing the variation of arc length, the process to alternately repeat the pulse electric current wave groups of both high peak in a short time and low peak in a long time to periodically change arc force at the same time has been studied. It has been found that the molten pool can be vibrated in a longitudinal direction also by the control of arc force and it has also been found that the generation of blowholes can significantly be reduced by this vibration. The vibration of molten pool is effective for the promotion of removal of not only the blowholes to be caused by generation of zinc gas but also those of supersaturation type by the nitrogen to be formed on the metal surface in the progress of their solidification.
Shear test has been carried out with same solders as those used in the previous paper in order to investigate the relation between thermal fatigue life of flip chip joints and shear properties of several solders. Shear strength decreased as the temperature changed from 23°C to 100°C in almost solders. However, in the case of pure indium, shear strength decreased little by changing the temperature. Indium and indium based solders such as In-48Sn and In-3Ag showed an excellent ductility under the conditions employed in this study. Fractography demonstrated that the fracture was mainly caused by the creep deformation. It is found that the lower the creep strength of solders, the longer their thermal fatigue life. The fact that parameter γ/τ (steady state shear rate/steady state shear stress) at 23°C is proportional to the thermal fatigue life strongly suggests that the latter can be predicted from the former.
In this research, diffusion bonding of the intermetallic compound TiAl containing Fe, V, B and SACM645 steel was investigated. Relationships between strength characteristics and bonding parameters were analyzed. Main results obtained are as follows, (1) Direct diffusion bonding of TiAl and SACM645 was possible, high strength joints were obtained by selecting short bonding time with the bonding temperature in the range of 1223-1283K. (2) In the bonding interface, two or three inter-layers were formed as diffusion process proceeded. Decarburized layer at the steel side, Fe-Al-Ti type layer and TiC layer at the TiAl side were formed. (3) High strength joints were obtained by suppressing the formation of TiC compound in the bonding interface and by controlling total width of inter-layers within 5μm.
In the CO2 gas shielded arc welding, spatters are scattered around and bonded to the surface of base metal, and it is still unclear what are the main factors of the difference of their bonding force. In this paper we examined the bonding force of spatters, which were bonded on the surface of base metal (SS400) in different conditions and temperatures in the CO2 gas shielded arc welding (using the solid wire of 1.2 mm in diameter). The conditions of the surface of base metal were as follows: (1) The surface has scale, (2) The scale of the surface was removed with the surface grinder (Rmax=0.6μm), (3) The ground surface was fumed, and (4) The scale of the surface was removed with the disc grinder (Rmax=7-16μm). The temperature of base metal was raised by the ceramic heating unit of 14 mm in diameter, which was set up at the back of base metal. The bonding force was measured through the shear force of the spatter. 400 spatters were examined on each surface. Most of the dimeters of the spatters were 0.4 to 1.4 mm. When the temperature of base metal was below about 450 K, spatters on the surface with scale was not hot enough to melt the base metal and could not bond there by melting the surface of base metal. Most of their shear stresses were below about 40 MPa, but as the temperature raised, the shear stress was increased up to nearly (300) MPa. The fume on the surface or the roughness of the surface did not affect the bonding force as directly as the scale on the surface. The temperature, however, affected the bonding force. When the temperature of base metal was below 450 K, the bonding force became a little smaller. When the spatter bonded on the surface, because of the heat transfer, the change of the microstructure and correspondingly hardening was found to occur. When the spatter and the heat-affected zones of base metal were examined, their Vickers hardnesses indicated a little higher value (some spatters had the value of 470 (Hv)) than the hardness of base metal (156-165 (Hv)), although it depended on the conditions of the surface and the temperature.
As for plants, higher operation temperature is required so as to attain higher efficiency. The plant construction material requires not only good mechanical property at higher temperature but also better oxidation resistantce. It has become difficult to satisfy these requirements simultaneously by a single bulk material. One of the countermeasures is surface treatment such as PTA (Plasma transferred arc weldinhg), CVD (Chemical vapor deposition), PVD (Physical vapor deposition) and so on. Among surface treatment laser cladding is one of the outstanding methods because its higher power density enables to clad refractory materials or even ceramics. However, there has been little work on the oxidation behavior of laser clad NiCrA1Y layer. Therefore the oxidation behavior of laser clad NiCrAlY layer formed with single layer so as to take account of the influence of dilution from the substrate. Influence of Al content and heat treatment were also investigated. The results obtained are as follows; (1) The oxide formed on the NiCr10A1Y and NiCr20AlY clad layers was mainly α-Al2O3 and the growth rate of the oxide obeys parabolic rate law. (2) The parabolic rate constant of the NiCr10AlY clad layer is approximately the same with that of the bulk material, but that of the NiCr20AlY clad layer is larger by 1-2 orders of magnitude. The difference in parablic rate constant is caused by the formation of unstable faster growing θ-Al2O3 on NiCr20AlY clad layer at the initial stage of the oxidation. (3) The heat treatment makes the distribution of aluminum in the clad layer more homogenious which enhances the nucleation of Al2O3 at the initial stage of the oxidation, resulting in the lower parabolic rate constant.
MoSi2 of which melting point was high and which had excellence oxidation-resistance at high temperature was studied. MoSi2 powder was deposited by low pressure plasma thermal spraying on the specimen with 50%Ni-50%Cr based coat after blasted on SS400 substrate. Then, residual stress generated in the specimen was determined. Compressive stress was produced in MoSi2 spray deposit. Tensile stress was produced in 50%Ni-50%Cr spray deposit except at the surface of SS400 substrate. A series of the experiments were done so as to elucidate the validity of the obtained residual stress distribution. Blasting on SS400 substrate, residual stress near the surface of the substrate was compressive and that of the inner part was tensile. After the blast treatment on SS400 substrate, depositing on the substrate with 50%Ni-50%Cr, residual stress in spray deposit was tensile. This was because SS400 substrate restricted the contraction of 50%Ni-50%Cr spray deposit which had large thermal shrinkage. Depositing MoSi2 after the blast treatment, compressive stress was generated in the. spray deposit. This was because the linear expansion coefficient of MoSi2 was extremely small comparing to that of the substrate nevertheless the temperature of the spray deposit was higher than that of SS400 substrate. As the result, the spray deposit restricted thermal shrinkage of SS400 substrate. Obtaining residual stress produced by the thermal spraying, the importance of measuring the elastic modulus of sprayed deposit was indicated.
Mechanical properties and tensile deformation behavior have been investigated on Sn-Ag-Bi system lead-free solders. Tensile deformation behavior was evaluated by strain rate changing method to estimate the thermal fatigue properties of the alloys. Tensile tests were conducted on cast solders shaped into rod type tensile specimens at room temperature. Strain rate was changed repeatedly during the test to obtain strain rate sensitivity index (m). The addition of bismuth up to 5% to Sn-3.5Ag eutectic remarkably increases the tensile strength, however, it drastically lowers elongation, especially the elongation becomes lower than 10% after aging at 393 K for 605 ks. Further addition of bismuth up to 15% gave only a little effect on tensile strength and elongation. The solution hardening of bismuth in tin is the main reason of the high strength of bismuth added alloys, because the increment of the lattice constant of tin well coincided with the change in tensile strength. The plots of m vs. strain where m was measured showed linear relations, therefore, the m value at strain zero (m0) and the gradient of the line (k) were obtained by extrapolating the line to strain zero. The lower values of m0 and positive low values of k have been believed to have excellent thermal fatigue resistance. The m value was decreased by addition of bismuth, however, it increased k. After aging the alloys more than 5%Bi, the gradient k showed negative values, indicating the alloys became susceptible to cracking, therefore, these alloys are believed to have inferior resistance to thermal fatigue. The alloys with 2% Bi showed lower m0 and lower k than Sn-3.5Ag, therefore, the alloy is estimated to have superior or similar thermal fatigue properties to Sn-3.5Ag, however, the melting temperature range is rather high.
The effect of surface cleanness upon ultrasonic bondability was investigated, in order to obtain a reliable micro-bond with high strength and small deformation when bonding was done at low temperature and low energy conditions. Au, Cu and Al physical vapor deposition films on a Si wafer, which are materials with different oxidizing characteristics, were selected for bonding pads. At first, the bonding surfaces of the Au, Cu and Al films were treated for contamination by cleaning, and the surfaces were quantitatively analyzed by Auger electron spectroscopy. After that an Au wire was ultrasonic ball bonded onto each surface in air or pure N2 gas, and the fracture mode of the Au ball bond in a pull test and the bond strength of it in a shear test were investigated. Then ultrasonic bondability was evaluated from the ultrasonic power by which the pull strength of the Au ball bond rose above the Au wire strength, and from the probability of which the pull strength of it rose above the Au wire strength at a ultrasonic power. Additionally, the surface cleanness of Au, Cu and Al films was investigated for the films exposed to pure N2 gas or air after being cleaned by ion bombardment and the films with a contaminated surface obtained by immersion in water and acetone. Main results are as follows. (1) The ultrasonic ball bondability of an Au wire onto an Au film at 373K in air is improved by cleaning the Au film surface by ion bombardment before bonding, but it onto an Al film is not improved so much by cleaning the Al film surface. (2) The ultrasonic ball bondability of an Au wire onto Au and Al uncleaned films in pure N2 gas was better than it onto Au and Al films cleaned by ion bombardment before bonding in air. This means that the ambient gas influences the bondability much more than the cleanness of a bonding surface. (3) Therefore, it is important to clean a bonding surface and change an ambient gas to a pure and dry gas for obtaining a reliable bond in ultrasonic bonding of an Au wire onto an Au pad at low temperature and low energy conditions, and it is important to change an ambient gas to a pure and dry gas in the case of an Al pad.
Copper base alloys, containing 2.4mass%Fe and 0.1mass%Zn, etc, were soldered using Pb-63%mass%Sn and then heated at 100°C, 125°C and 150°C for 1000-2000h to grow intermetallic compounds at the solder/alloy interfase. Elemental analysis at the interfase was performed by using EPMA. The fractured interfase, where the solder was peeld off after the 30° bending test, was observed by optical microscopy, and the concentrated elements were analyzed by EPMA. The copper alloy containing Fe, Zn showed a higher intermetallic compound growth rate, thus larger decreasing in the peel strength at the soldered joint. Intermetallic compounds formed at the solder-copper alloy interface were found to be typically, at the solder side, η-cu6sn5, and, at the copper alloy side, ε-cu3sn in which Iron element was found to have been segregated.