High residual stresses are known to exist in the ceramic part near the ceramic-metal joint. However, in carrying out their measurement, we sometimes find it very difficult to get a tendency in stress distribution. One of the reasons for the difficulty seems likely to be the presence of residual stresses produced when ceramic material is sintered. These initial stresses are considered to affect the residual stresses caused by brazing. In this study we measured both residual stresses before and after brazing and then examined if the measured stress values are Proper as such. For this purpose, we compared the result of computer simulation, that of a 4-point bending test, and the measured stress values with one another. As a result, we found out the following. (1) Over 180 MPa of residual stress was measured in the surface layer of the as-sintered silicon nitride. The area of the stress concentration was as small as below 1.0 mm in diameter. (2) The stress distribution obtained by subtracting the initial stresses before brazing from the residual stresses measured after brazing agreed with the simulation result qualitatively. (3) The tensile residual stress measured with a micro X-ray beam was about 270 MPa at maximum at a point 0.2 mm away from the interface. The strength of the silicon nitride decreased by 335 MPa due to brazing. (4) The cracking position roughly agreed with the point where the maximum principal stress was measured. The direction of cracking also agreed with the normal to the direction of the maximum principal stress.
Brazeability and the reaction between base metal containing magnesium and non-corrosive flux have been investigated in relations to the magnesium content in base metal, brazing temperature and holding time. The flux used was KAIF4-K2A1F5⋅H20 system non-corroxive flux. Brazeability was evaluated by the fillet formation test on tee type specimen consisted of vertical member of brazing sheet and horizontal member of base metal. Brazing was conducted in high purity argon gas atmosphere and maintained at 873 K for 300 s. The increase in magnesium content in base metal drastically lowered the fillet formability, moreover, the flux penetrated into magnesium containing base metal preferentially along grain boundaries. The flux reacted with magnesium in base metal and formed compounds of KMgF3 and MgF2. The poor brazeability of the alloys with magnesium is attributable to the reaction between flux and magnesium that consumes the amount of supplied flux resulted in the lower efficacy of flux. The penetration depth of flux into base metal depended on the holding time and temperature, espcially the depth was remarkably affected by the spread area of flux, i.e., the amount of supplied flux per unit area. The wide spreading at higher temperature reduced the penetration, whereas the small spread area at lower temperature enhanced the penetration depth. Accordingly, the plots between the penetration depth and the square root of holding time showed parabolic relations that indicates the consumption of flux. The consumption of flux resulted in the combination of oxygen with compounds.
In this paper we studied the loci and the velocities of scattering spatters in shielded metal arc welding with high titanium oxide type electrode. We examined only spatters that flew off in the right-angle direction to the weld line and passed through the slit of 4 mm by 75 mm. The loci of the spatters were photographed when they scattered in the air, and their velocities were calculated using their times of photographing. And we simulated the loci and velocities of the spatters. The experimental data and calculated values were compared. In the experiment we examined 110 spatters, and their particle diameters range from 0.1 to 1 mm. The spatters flew around on the surface of base metal within a 500 mm radius circle. They flew in the air for less than about 0.5 seconds. And the highest velocity was 6 m/sec. The Reynolds numbers of the spatters were less than 7. They were given by Re=d×V/ν (d is the diameter of a spatter, V is the velocity of the spatter, ν is coefficient of kinematic velocity). And the coefficient of kinematic viscosity of the air was calculated using the temperature. The temperature was determined by the arithmetic mean of the temperature of spatters (given they were 1637 K) and the temperature of the air (293 K). To simulate the loci and the velocities of the spatters, the equation of motion was set up under a certain condition. The condition is that the temperatures of the scattering spatters are constant and their drag coefficients (Cd) are given by the Stokes equation for a sphere (Cd=24/Re). The calculated value by this equation matches well the experimental results, though the former was a little larger than the latter in almost all the cases.
If an arc length in high speed pulsed MAG welding is too long, undercuts and/or humping are generated and if it is too short, spatters are generated. As for the contradictory problem above, by refining the droplets from a wire and maintaining one droplet transfer per pulse at the same time, the short-circuiting in a short arc could be avoided and then, the prevention of spatters and high speed & high efficient welding became compatible with each other. As the basic means to refine droplets, the increase of two factors such as an electromagnetic pinch force to be applied to droplets and deformability of droplets with the same degree of an electromagnetic pinch force was examined. As the result of setting the simple rectangular wave pulse of high peak current in a short time using an inverter type pulsed power source under the constant diameter of a wire in order to increase an electromagnetic pinch force, one droplet transfer per pulse became possible upon condition that the volume of droplets decreases by about 30% than that in case of using the conventional power source with the secondary side chopping transistor. Furthermore, for the sake of increasing the deformability of droplets, the chemical compositions of the wire possible to transfer one droplet per pulse on condition that the volume of droplets decreases by 20% were found among those of various prototype-wires. Moreover, the droplets above showed the same surface tension as that of the conventional droplets and lower coefficient of viscosity. By the combination of pulsed current wave form and the improvement of wire physical properties, it is possible to decrease the volume of droplets to about a half of that of the conventional droplets. As the results, the increase of welding speed limit by more than 20% for no generation of both spatters and weld defects was shown and the achievement above was immediately applied to the actual mass-production line.
In a previous report, different temperature distributions in Ar-H2 mixed gas tungsten arc had been evaluated from an argon atom line (Ar I), hydrogen atom line (H I) and ionized argon line (Ar II) intensities by emission spectroscopic measurements. In order to find a solution to these inconsistent results, a new spectroscopic method (named as Ar I-H I correlation method) was developed in which the temperature was estimated from the correlation between Ar I and H I intensities in the assumption of a local thermodynamic equilibrium (LTE) and heterogeneous of plasma gas composition. The temperature distribution by the Ar I-H I correlation method showed good agreement with that by the Ar I-Ar II correlation method reported in another paper. From this fact, it was shown that the consistent temperature distribution was led using Ar I, Ar II and H I line intensities. Furthermore, electron density distributions were determined without the assumption of LTE by both Stark broadening method of hydrogen atom line Hβ and method of infrared plasma diagnostics, and showed good agreement with electron density distributions calculated using Saha relations from the local plasma gas composition and temperature obtained by Ar I-H I correlation method. All of the results led to the conclusion that the performed spectroscopic analysis of argon-hydrogen gas arc plasma, under the assumption of LTE, was valid and effective, and that the hydrogen gas concentrated near the cathode and the temperatures in the whole plasma region was remarkably lower than the temperatures in a pure argon gas arc.
Cladding techniques have been used in many areas. Recently laser cladding techniques have been developed and applied to the automobile parts fabrication and to the repair of pipes inside installed in the Nuclear Power Plants. As for the laser cladding, there are the following three methods of supplying the cladding material ; (1) Wire feed, (2) Powder feed and (3) Preplaced powder. The third method was selected for having higher flexibility in selecting the chemical composition of cladding material and cladding position. The investigation was carried out to produce a NiCrAlY cladding layer. Cladding parameters such as laser power, traveling speed, diameter of powder and cladding atmosphere were changed systematically to select the best condition for a single bead with a low power (1200 W) CO2 laser. A SUS304 plate with a 12 mm thickness was used as a substrate, and mixed powders were bedded with a 1 mm thickness with an organic binder. The dilution ratio and the cross sectional area of the cladded layer were measured and the best cladding conditions were selected on the basis of these data. To get a large cladded area a weaving method and a half lapping method were tried based on the best cladding conditions for the single bead. The results obtained are as follows ; 1. The NiCrAIY laser cladded layer with good characteristic can be obtained by mixing commercial powders of Ni-Cr, Al and Y-Ni and a commercial organic binder. 2. With the weaving method, a broad area can be cladded with a low power (1200w) CO2 laser. 3. The uniform distribution of chemical composition throughout the cladded layer thickness can be obtained. 4. An atmospheric chamber replaced inside with Ar can make the layer's contour better. 5. Fine powder was preferred from the points of view of the dilution ratio and the cross sectional area of cladded layer. 6. Carbon content of the cladded layer was not so high although the organic binder was used as the binder, and this shows the high possibility of this method to prepare corrosion resistant cladded layer.
This paper gives a method to experimentally determine the dynamic characteristics of arc sensor in GMA welding in dip transfer mode. The method mainly involves a vibration device to excite sinusoidal wave forms of torch height and data processing by means of FIR digital low-pass filter as well as digital fourier transformation (DFT). Experimental results show that the sensitivities of arc sensor are quite greater than that in DC open arc welding. The response of welding current to the variation in torch height gets to reach the highest level at around 3 Hz in our experiments. Although the response continues to hold higher level when the frequency exceeds about 5-6 Hz, the SN ratio becomes poorer than that at 3 Hz. The response of welding current shows a delayed phase relative to the variation in torch height. Contrary to this, the response of welding voltage has an advanced phase relative to the variation in torch height, and the response becomes higher and higher with the increase of the variation frequency of torch height, but it's SN ratio is quite poorer than that of the response of welding current. To clarify the effects of shielding gases on the arc sensor, experiments were made by using different mixed gases of Ar and CO2. It is found that contrary to these in open arc welding, the responses in short-circuit arc welding using pure Ar are higher than that using mixed gases of Ar and CO2. Simulation analysis was also made based on an arc sensor's model proposed by authors for the short-circuit arc welding. The results displayed that the theoretical and experimental results are quite similar in qualitatively but did not yet achieve agreement quantitatively. The theorectical results also show that not only the average short-circuit frequency, but also the change rate of the short-circuit frequency induced by the variation in arc length have great effect on the sensitivities of the arc sensor.
Solidification behaviors of austenitic stainless steel weld metals near fusion boundaries were studied, in which the epitaxial growth and the selection of primary phase were of main interest. In the AF solidification mode, planar austenite grows epitaxially from austenite grains in the base metal. Subsequently ferrite forms at dendrite boundaries of the primary austenite after the austenite changes from planar to dendritic. In the FA solidification mode, planar austenite grows epitaxially from austenite grains in the base metal as a result of competition between ferrite nucleation and austenite growth. Then ferrite nucleation is followed because of the enrichment of Cr in the liquid, and continues to grow eventually as the primary phase. The ferrite has the K-S relationship with the planar austenite. In the stage of primary ferrite solidification, austenite sodilifies as the second phase at dendrite boundaries, and has the same crystallographic orientation as the original planar austenite. In the sample which solidifies as FA mode with the lowest Cr/Ni ratio, it is possible for austenite to solidify even as the primary phase because of the fluctuations of solutes in the liquid and the change of undercooling due to local change in temperature gradient in the liquid.
In Fe-Cr-Ni stainless steel weld metals which solidify as ferritic single phase, austenite first precipitates at ferrite grain boundaries on cooling. Then continuous intergranular austenite is formed by the coalescence of globular austenite along grain boundaries. The austenite has the K-S relationship with ferrite of both side, selecting different combinations of close-packed plane and direction for each ferrite. Subsequently, Widmanstatten austenite, which has the same cystallographic characteris-tics of the intergranular austenite, grow into the ferrite grain. In duplex stainless steel weld metals containing nitrogen, intragranular austenite precipitates after the formation of intergranular austenite. Diffusion of nitrogen primarily controls the precipitation of both inter- and intragranular austenite. With increasing Cr and Ni contents, the precipitation of the intragranular austenite increase due to the increase in microsegregation during solidification.
In austenitic stainless steel weld metals solidified as ferritic single phase, subsequent ferrite-to-austenite transformation could be massive when the postsolidification cooling is rapid as in GTA welding. On the other hand, this GTA weld metal shows acicular structure of ferrite and austenite at room temperature microstructure. The effect of massive transformation on the formation of acicular structure was investigated in this study using different thermal cycle patterns and quenching technique. Massive transformation occurs below the T0 temperature within the two-phase region of ferrite and austenite at a cooling rate of approximately 100K/sec. On cooling after the massive transformation, austenite continues to grow into retained ferrite epitaxially from massive austenite while ferrite precipitates again at twin boundaries within the massive austenite. This suggests that acicular structure of ferrite and austenite is formed even if the massive transformation occur. In this case, the grain refinement and rapid progress of structure formation are expected as compared with weld metals in which massive transformation does not occur.
One-pass submerged arc welding (SAW) with high heat-input is widely employed for the corner seam of box-shaped columns, however, an internal crack similar to lamellar tearing occasionally occurs along the center-thickness line of the flange plate. In this paper, microstructures, hydrogen concentrations and residual stresses at the cracking position have been investigated to clarify the mechanism of the cracking. In addition, appropriate countermeasures against the cracking in terms of the quality of plates and the conditions of welding have been studied, by application of the one-pass SAW experiment in the laboratory and the numerical analysis of hydrogen diffusion. The generation and the propagation of the cracking were closely related to the transit of hydrogen concentration at the cracking position, while the effect of residual stresses on the cracking was small. The dominant material factors of this cracking were elongated manganese sulfides (MnS) in the center segregation band, and martensite-austenite constituents (M-A) around MnS formed by intercritical heat affection of one-pass SAW. Moisture contained in the flux was the greatest source of hydrogen, so that drying of the flux was the most effective countermeasure in the welding conditions. As a groove for the one-pass SAW corner joint, a bevel groove was preferable to a V groove to prevent cracking. PWHT at 300°C for longer than 2 hours was also effective. As countermeasures in the production of steel plates, alleviating center segregation by soft reduction in continuous casting, shape control of sulfides by addition of Ca, and lowering Ceq by application of thermo-mechanical-control-process were effective.
The effects of base metal grain size on base metal dissolution and isothermal solidification of Ni-base superalloy, CMSX-2 were investigated employing MBF-80 insert metal. TLP-bonding of single crystal, coarse-grained and fine-grained CMSX-2 was carried out at 1373 K-1523 K for various holding times in vacuum. The dissolution phenomena of base metal were followed by Nernst-Brunner's theory in any base metal grain sizes. The saturation time for dissolution and the saturated dissolution width of base metal decreased in the order; single crystal, coarse-grained and fine-grained base metals. The eutectic width decreased linearly with the square root of holding time during the isothermal solidification process for single crystal, coarse-grained and fine-grained base metals. The completion time for isothermal solidification decreased in the order; single crystal, coarse-grained and fine-grained base metals. The difference of isothermal solidification rates produced when bonding the different base metals could be explained quantitatively by the effect of base metal grain boundaries on the apparent average diffusion coefficient of boron in CMSX-2.
Metallization method of AlN substrate by ion plating technique has been developed. Dual coating films of 5-10 μm thick nitrides (TiN, ZrN and CrN) and 10 μm thick copper were formed on the AlN substrate by ion plating. The functionally gradient films of TiN Ti were also deposited on the AlN substrate. The adherent strength of metallized films against AlN substrate was evaluated by the tensile test at room temperature. The morphologies of nitride films were quite sound and they were stuck AlN together well. Element analyses by EPMA and ESCA revealed that nitrides such as TiN, ZrN and CrN were hardly reacted with AlN substrate or Cu film. The adherent strength of TiN, ZrN, CrN coating film and the functionally gradient films indicated the average values of 50-60 MPa in any cases. The joint strength of TIN+Cu dual metallized AlN to copper soldered by Sn-38 mass%Pb solder was about 33 MPa.
Laser surface melting treatment was applied to the sensitized Type 308 stainless steel weld metal in order to improve its intergranular corrosion resistance in the sensitized Type 308 stainless steel weld metal. The treatment was performed by a CO2 laser generator with the maximum power of 2.5 kW. Argon was used for the shielding gas in the laser treatment. The degree of sensitization was examined by the EPR method. Prior to the laser treatment, the specimens were sensitized at 773 K for 30 ks in order to imitate the condition to cause low temperature sensitization in stainless steel weld metals. Experimental results indicated that the sensitized weld metal restored a complete corrosion resistance to intergranular corrosion by the laser treatment at the higher laser traveling velocity, whereas the improving effect was insufficient at the lower laser traveling velocity. Owing to the microstructural analysis by a SEM, serious corroded regions were found at the heat affected region of following pass in the laser treatment with lower laser traveling velocity. The microstructural analysis by a TEM revealed that chromium carbide which caused the deterioration of corrosion resistance precipitated at δ/y boundary in laser treated weld metal. These results indicated that chromium carbides precipitated in the HAZ of following laser treating pass with the low cooling rate, and resensitization occurred by the precipitation of chromium carbides during the laser treatment. Consequently, when laser treated region was heat-treated again aftr laser treatment, re-sensitization took place relatively early. These results suggest that, in the case of δ-ferrite existing in the laser treated region, the precipitation of chromium carbides during the thermal cycle of low cooling rate and the haet-treatment after the laser treatment was promoted by δ-ferrite.
Improvement in mechanical properties of transient liquid phase (TLP) bonded joints of HP alloy at the elevated temperature was investigated employing newly developed insert metal. TLP-bonding was carried out at 1403-1463 K for 600s in vacuum. The chemical compositions of insert metal were optimized by the mathematical programming method. The objective function which was introduced as an index of performance of insert metals involved the melting point of insert metal, the strength (hardness) and formability of microconstituents in the bonding layer as the evaluating factors. A composition of Ni-3% Cr-4% Si-3% B which optimized the objective function was determined. SEM observation revealed that the microstructure in bonding layer using the newly developed insert metal indicated a sound morphology without forming microconstituents such as Cr7 (C, B)3. The tensile properties of joint at 1273 K were comparable to those of base metal in the bonding temperature range of 1423-1463 K. The fractured of the joints bonded at 1423-1463 K occurred in the base metal substrate, while the joint bonded at 1403 K, which tensile properties were fairly deteriorated compared with the base metal, fractured at the bonding interface.
The effects of alloying elements on the morphology of interfacial oxides in the diffusion-bonded joint have been investigated mainly by TEM observations for Al binary alloys containing 0.06-2.0 at%Mg, 1.0 at%Si, 0.5 at%Mn, 1.0 at%Zn, and 1.0 at% Cu. At the joint interfaces of the Al binary alloys except for those of the Al-Mg system, continuous amorphous oxide films were observed at all bonding temperatures employed in this investigation. At the joint interfaces of the Al-Mg alloys, as described in a previous paper, the oxide at the joint interface altered gradually from amorphous films to crystalline particles 10-100 nm in size as the bonding temperature was increased. The difference in the behavior of interfacial oxide between the Al-Mg alloys and those of the other alloys can be explained thermodynamically by assuming that crystalline oxides were formed through reductive reactions of the superficial oxide film of Al by Mg. EDS analyses of the amorphous oxide film at joint interfaces of the alloys revealed that Mg atoms were concentrated in the amorphous oxide film of the Al-Mg alloys prior to the formation of the crystalline oxide particles, whereas no concentration of other alloying elements could be detected in the amorphous oxide film of the other alloys.
The low-pressure plasma spray coating process has been established in the field of gas turbines and is used for parts (turbine blades, duct segments, etc.) which are exposed to corrosive gases at high temperatures. Overlay coatings based on the MCrAlY alloy system (M is Ni, Co or Fe) are commonly employed as oxidation- and corrosion-resistant coatings. Mechanical properties, such as high-cycle fatigue lives, of CoCrAlY, NiCrAlY and CoNiCrAlY coated systems were investigated at high-temperature as compared with the uncoated substrate such as conventional IN738LC, unidirectional solidified CM247LC and single crystal CMSX-2. High-cycle fatigue properties of the MCrAlY coated superalloys at high-temperature (IN738LC : 1123 K, CM247LC, CMSX-2: 1173 K) showed inferior performance in comparison with the uncoated results. It was because that the high-cycle fatigue cracks initiated at interface defects, such as pores and grit residues, between the coating and the substrate in any cases. The high-cycle fatigue crack could be observed to grow into the MCrAlY coating, and then into the substrate. It seems to be impossible to evaluate the high-cycle fatigue lives of the MCrAlY coated superalloys at high-temperature by using the uncoated results.
Fatigue crack propagation rates of SB450 steel plate were measured at a stress ratio of 0. The fatigue crack propagated through the weld metal or the base metal at room temperature and 300°C in air. In order to perform the high temperature test, a special furnace was made. The furnace achieved the proper distrbution of temperature, which reduced the compressive thermal sterss near the center portion of specimen below 1 MPa. The low thermal stress condition avoided the enhancement of fatigue crack closure. Finally, the same fatigue crack propagation properties were obtained at room temperature and 300°C.
JJ1 type austenitic stainless steel is emerging as the preferred structural material for superconducting magnet casings to operate at liquid helium temperature (4K). In order to evaluate the cryogenic fracture toughness and the temperature rise of tangsten inertgas (TIG) weld in 200 mm thick forged JJ1 type austenitic stainless steel plate for fusion reactor magnets of the next generation, elastic-plastic fracture toughness (JIC) tests were performed with 1T compact tension specimens at 4K. Testing was conducted in accordance with ASTM standards E813-87 for determining JIC using the unloading compliance technique to monitor crack growth. Au/0.07% Fe -Chromel thermocouples were used to measure the temperature rise near the crack tip. The effects of specimen location and nitrogen content on JIC are examined. Specimens were subjected to scanning electron microscopy (SEM) after fracture testing. The effect of inclusion content on the elastic-plastic fracture toughness parameters (JQ, JIC) is also discussed using optical microscopy and energy dispersive X-ray spectrometer (EDX).
This report considers the low melting point Au-Sn microsoldering (bonding heat tool temp. 523 K and time is 5 sec.) which is applied to the 400 pin count and 0.2 mm lead pitch TCP (Tape Carrier Package) assembling. This method is performed by heat and press tool gang bonding of tin electroplated (6.5 μm thick) copper pattern on substrate and gold electroplated (1.0, μm thick) TCP outer lead with non flux in air. Au-Sn microsoldered layer has the high peel strength and has the high reliability in 423 K storage in air that is higher than Sn-37 mass%Pb microsoldering. And the organic glass-epoxy (FR-4) substrate is not damaged after the Au-Sn microsoldering.
In semiconductor devices the gold wire bonding to aluminium pads is a widely used bonding practice. The reliability of bond strength exerts a strong influence on that of IC or LSI. Voids formed in gold-aluminium intermetallic compounds are known to degrade the long-term reliability of gold wire bonds to aluminium pads. In this reliability, the annealing envirenment has great influence on the behavior of this voiding as well as the intermetallic formation. The influence of annealing condition for gold-aluminium bonds was investigated comparing with the encapsulated condition and decapped condition. Great differences were found between two conditions. In the case that initial shear strength is high, shear strength was high even after annealling in 200C-1000hr for decapped devices. However, in the case of encapsulated condition shear strength was degraded after annealling in 200C-100hr. In the case of encapsulated condition, intermetallic compounds was corroded by bromine included in resin. And this corroded compound degraded gold-aluminium bonding. On the other hand, in the case that initial shear strength is low, shear strength became low after annealling in 200C-100hr for both conditions. In conclusion, shear strength was degraded after annealling in 200C-100hr for encapsulated condition, irrelevant to bonding conditions.