Electro-magnetic flow pressure in the mercury pool was tested in various containers and conditions. The total pressure P along the center line was measured by the Pitot tube at the distance z from electrode tip. Obtained results showed that P increased proportionally to (I/D)2 at the fixed z, and P/(I/D)2=a-bz, a and b are dependent on the test container, especially current flow pattern. Low temperature fusible metal (Wood's metal) was melted by the soldering iron of various shape of copper rod, through which heat and current were applied on the metal. The width/depth ratio of penetration was nearly 2 at zero current, while it increased considerably with increase in time and (I/D)2 values. Cause of axial force acting on the pendent drop in welding was considered. It is the dynamic pressure due to electro-magnetic pressure difference in diverging currentfield.
Cast iron is one of difficult material to weld. After welding of cast iron material, the heat-affected zone has higher hardness, martensite structure and high cracking susceptibility for high carbon contents. The base metal used in this study was the nodular graphite cast iron bar (JIS type FCD 600) and the material of the thermal spray was the self-fluxine alloy (S.F.A.). In this paper, the principal objective of the experimental study was to obtain the basic data for investigation of the mechanical and metallurgical properties. The experimental findings may be summarized as follows : (1) The maximum tensile strength reached about 480 MPa of which is about 80% of the tensile strength of the base metal. (2) The Vickers hardness distribution near the heat-affected zone was about Hv400. (3) The micro structure near the heat-affected zone does not indicate transformation to white pig iron because of lower cooling rate. The structure around graphite is ferrite. (4) The tensile fracture surface shows a dimple fracture pattern at 1223 K peak temperature.
A numerical model for a deep penetration laser welding is developed. It consists of the quasisteady-state three dimensional heat flow model and the three dimensional keyhole surface model. In the model analysis, the recoil pressure due to vaporization is taken into account for the keyhole process and a line heat source of finite depth is proposed to estimate the heat input from the keyhole. Numerical results show that the vaporization of base metal affects the keyhole surface geometry and the depth of it affects molten pool profile remarkably. The calculated molten pool profiles are also compared with the experimental profiles and it is confirmed that this model is useful for the prediction of laser welded pool profile qualitatively.
It is said that the aluminum alloys with the content of magnesium more than approximately 0.5 mass% is difficult to be brazed and soldered. In this study, we attempted to solder the aluminum alloys, such as A5052 and A5056, which contain magnesium more than 2.5 mass% with the aid of ultrasonic vibration. The joining was performed in the air using no flux and a zinc plate as a filler metal. Those alloys were able to be soldered at the temperarures between the eutectic point in Al-Zn binary system and the melting point of zinc. The tensile strength of a joint decreased with increasing the applying time of ultrasonic vibration over 1 sec and the vibration amplitude over approximately 50 km. The Mg amount segregated to a faying surface and the tensile strength of a joint decreased with increasing the heating rate to the joining temperature.
A laminated and diffusion welded turbine vane with fine cooling passages was designed and manufactured using 18Cr-8Ni stainless steel wafers. The turbine vane produced, was assessed using coolant flow analysis. In order to improve the joint quality, investigations were carried out using conventional diffusion welding to join the stainless steel wafers and camparisons made with diffusion welding followed by hot isostatic pressure (HIP) treatment. The tensile strength of the diffusion welds increased as the welding pressure was raised. However, the use of higher welding pressure brings about large deformation at the joint. As a result it is difficult to use conventional diffusion welding to produce good quality joints without deformation of the cooling passages at the joint region. When the welding area ratio at the joint interface is approximately 50% only isolated voids remain at the joint. Therefore, the use of HIP treatment is able to remove residual voids from the joint interface without macro deformation of the turbine vane. The use of HIP treatment allows joints to be produced with greater than 50% welded area ratio and with only 0.5% change in total length. This study has shown that by applying HIP treatment after preliminary diffusion welding it is possible to produce joints with no residual voids and with a minimum change in component shape.
The swell-out phenomenon will occur at seal welding of a receptacle such as tubing which has some inner gas volume. This study has been conducted to make clear this phenomenon experimentally and to develop its preventative technology at the seal welding of Zircaloy-2 tubing. The swell-out ocurred at inside of welded metal when the pressure difference between inside and outside reached a critical value by increase of inside pressure, and the swell-out was developed toward outside as the pressure increased. We have developed a welding technology to effectively prevent the swell-out above.
In TIG welding of Zircaloy-2 tubing in an atmosphere in which the air partial pressure PAIR decreases with time as high purity inert gases are introduced into a chamber after evacuation to various pressure, the arc voltages were measured and the properties of welds were examined. The arc voltage increase as the PAIR in the welding atmosphere decreases. The nitrogen content [N] in the welded metal varies at each circumferentially devided zone, and a linear relation between the √PN2 and [N] was confirmed. The thickness of surface oxided layers after long time autoclave tests in water with high temperature and pressure are also measured and evaluated.
Research and development of grinding wheel bonded cBN·frfrit/Al2O3·frit (laped sintering) to outer surface of metal ring were conducted. Ag-Cu-Ti brazing was applied for bonding method in stead of conventional adhesive agent method. Main results obtAlned are as follows. (1) The relief of residual thermal stress and operating stress at joint are important. It was concluded by calculation of stress that use of Kovar for metal ring was effective for thermal stress relief at bonding and slit cutting to Kovar ring was effective for operating stress relief at rotating. (2) New grinding wheel fabricated with the above mentioned procedure rotated by peripheral speed 290 m/s at spin test. From this spin test result, it was confirmed that this wheel had excellent rotating characteristic compared with conventional wheel (adhesive agent method).
Detection process of the defect at the micro joints has been researched and developed based on that the temperature distribution of the joint surface is influenced by the degree of heat transfer coefficient at the interface by the laser irradiation with short duration. For micro-joints of QEP lead, etc. the defects can be shown to be detected theoretically and experimentally, and furthermore experimental results are confirmed by the computer simulation on thermal model of the joint.
The position and size of internal defect, optimal detection condition and minimum defect size on the inspection are investigated on the computer simulation on thermal model of the joint. The size and position of internal defect can be determined by the area of temperature above Tc on the joint surface, and then optimal detection condition (laser power, taking time of thermal image) are decided by the relation between temperature behavior of the joint under laser irradiation and characteristics of thermography. Furthermore, minimum defect size on the inspection is influenced by kinds, thickness of the lead and thermal transfer coefficient at the interface of the joint, and is nearly 50, urn in the case of the micro joint between cepper alloy lead with 150μm thickness and glass epoxy substrates (1.6 mm thickness).
Influence of the microstructure in the Heat-Affected Zone of plain carbon steels (S50C, S25C, S15C and SUYB steel) on stress relaxation behavior during the reheat treatment process were studied. The HAZ structure of plain carbon steels were made by the synthetic heat treatment. Two kinds of microstructures of the synthetic HAZ were prepared by Air Cooling (A.C) or Water Quenching (W.Q) treatment. Stress Relaxation tests were carrid out by means of three point bending method and constant-strain rate test on heating. The deformability of the synthetic HAZ structures at high temperature during the reheat treatment process were examined by constant-load test on heating. The relation between the precipitated behavior of carbides and the change of carbon concentration in the matrix of the synthetic HAZ were investigated during the reheat treatment process. The effect of this relationship on the stress relaxation behavior was discussed in terms of free from alloying elements of plain carbon steels. The results are summarized as follows. (1) Stress relaxation behavior during the reheat treatment process of 4 types of plain carbon steels were completely released. Influence of the microstructure in the synthetic HAZ on the stress relaxation behavior appeared in a manner of the delay of relaxation behavior of Ferritic-Pearlitic structures (A. C specimens) during the reheat treatment process. (2) The deformability of HAZ structure of carbon steels during the reheat treatment process were clearly low with A.C specimens of S50C steel as compared to another 3 types of plain carbon steels. These fractographs mode was a minor ductile fracture containing intergranular fracture surface. (3) The difference of stress relaxation behavior could be explained by the change of carbon concentration and carbide precipitated site in the matrix of both synthetic HAZ.
Formation of defects such as porous zone and crack in the reaction layer of Si3N4 to molybdenum joints was investigated using pressureless sintered (PLS-) and hot-pressed (HP-) Si3N4 with Cu-5%Cr, Cu-1%Nb and Cu-3%V insert metals.The obvious porous zone occurred in the reaction layer of PLS-Si3N4 to molybdenum joints when the reaction layer was relatively thick, while the porous zone did not occur in the reaction layer of HP-Si3N4 to molybdenum joints. The volume change with interfacial reaction between Si3N4 and the reaction layer was estimated from the analytical results of silicon content in the reaction layers. The volume after reaction was seemed to decrease to that before reaction in case that any insert metals were employed during bonding of PLS- and HP-Si3N4 to molybdenum. It was deduced that the porosity in Si3N4 substrate and the volume change before and after interfacial reaction were the important causes of the porous zone formation. The cracking in the reaction layer was appeared to be affected basically by the thermal stress generated during cooling process, and also to be promoted by the porous zone in the reaction layer which could be the stress concentration sources.
A type 329Jl duplex stainless steel was welded by gas tungsten arc welding in argon-nitrogen gas mixture atmospheres. The tensile properties and microstructures of the weld metals were examined. The nitrogen content increased and the ferrite content decreased with an increase of the nitrogen partial pressure of atmosphere. The ferrite content decreased linearly with an increase of nitrogen content. The tensile strength and elongation of the weld metal made with argon atmosphere were remarkably lower than those of the base material, but they increased with the increase of nitrogen content and were close to those of the base material at about 0.4 mass% nitrogen content. The fractography indicated that only the base material and high-nitrogen weld metals showed dimple patterns clearly. The crack paths in tensile-tested base material and high-nitrogen weld metals were complicated while those in the other weld metals were relatively straight. The tensile properties of weld metal were affected by the ferrite content and chromium nitride.
This study was carried out in order to develop a satisfactory technique for joining TiAl intermetallic compounds. Ti-38 mass% Al binary cast alloys were bonded in a vacuum of 26 mPa using the solid state diffusion bonding method by varying the bonding conditions, viz. the bonding temperature varied from 1273 to 1473 K, the bonding pressure varied from 10 to 30 MPa and the bonding time varied from 0.96 to 3.84 ks. From metallurgical point of view, the diffusion bonding diagrams with bonding conditions were produced in order to obtain a sound joint without microvoids and oxides at the bonded interface. According to these diagrams, the joints for mechanical testing were produced at the temperature of 1473 K for 3.84 ks with 15 MPa. The joint tensile strength at room temperature was about 225 MPa and the joints fractured in the base metal zone. However, the joints at the testing temperatures of 1073 and 1273 K fractured at the bonded interface and the joint tensile strength was about 40 MPa lower than that of the base metal, because minimal bonded interface migration occurred. The joints recrystallized at the bonded zone were produced in order to promote the migration of the bonded interface and sequently improved the tensile property at 1273 K for the joint with the previous bonding conditions and with the post-bonding heat-treatments. The joint tensile strength at 1273 K with recrystallized grain size of around 130 μm was about 210 MPa and the joints fractured in the base metal zone departed from the bonded zone even at 1273 K.
Residual stress and angular distorsion are very important problems in welding design and fabrication. In the previous reports it was shown that the materials with a martensitic transformation at low temperature were effective to reduce the anguler distorsion and deformation in welding. In this report the effects of transformation on residual stresses were examined. The results are shown as follows; (1) Residual stresses are closely related to transformation (transformation expansion and superplasticitiy) in welding and compressive stresses were measured at the surface of weld metal for a few welding electrodes with the low transformation temperature. (2) The materials with the transformation at low temperature are effective to reduce the residual stress in welding. In this study, the residual stresses of the weld metal with the transformation temperature of 200-300°C showed the minimun value. (3) It is possible to reduce both the residual stress and anguler distorsion in welding at the same time by use of the welding material with transformation at low temperature.
Residual stresses and angular distorsions are very important probrems in welding design and fabrication. In the previous reports it was shown that the materials with a martensitic transformation at low temperature were effective to the reduce residual stress and anguler distorsion in welding. In this report the effects of transformation on prevention against crack in welding were examined by use of restraint thermal cycle test and constraint crack test. The results are shown as follows; (1) The materials with transformation at low temperature were effective to reduce residual stresses in stress concetration area and to prevent cracks in welding. (2) As the result of the stress consentration test (mild steel was broken in the midst of cooling by this test method), it was possible to prevent a crack or a failure at the stress concentration area by use of the materials with the transformation at low temperature. In this case, the transformation superplasticity was more effecive than transformation expansion to release the stress concentration. (3) The Ms temperature of the materials with the transformation at low temperature (there was no crack by use of these materials in this test) was less than 200°C. But a dilution from a base metal raised the transformation temperature and the free thermal contraction curve changed. Therefore in welding practices, the change of transformation temperature by the dilution from base metal is also important.
A distribution pattern of inherent strains in long bead-on-plate welds, which has 3 unknown parameters for each inherent strain component, is proposed. Based on the proposed distribution pattern of inherent strains, the measurements for three dimensional residual stresses can be done as followings. (1) 3 pieces of specimens T, Ly and Lz (named TLyLz Method) are cut from bead-on-plate weld and three dimensional inherent strain components are separated. (2) Measurements are performed on T, Ly and Lz specimens respectively to estimate the inherent strain zones and the unknown parameters for their distributions. (3) Three dimensional residual stresses are computed by using the inherent strains measured in step 2). When inherent strains distribute in all thickness of plate, the measurements are performed only on T specimen (named T Method), and the inherent strain zones and their distributions can be estimated. To verify TLyLz method and T method, numerical experiment and actual measurement are carried out respectively for mild steel and stainless steel bead-on-plate welds. The measured residual stresses by the new methods show very good accuracy compared with the values computed by thermal elastic-plastic analysis and those directly measured on the surface.
In order to investigate the effects of defect size at root region on fatigue strength of non-load-carrying cruciform fillet welded joints, finite element analysis, fatigue test and hardness test were carried out. Main results obtained are summarized as follows: (1) It was confirmed that a fillet welded joint had fatigue limit 1.4-2.5 times as large as that of a joint as welded by TIG treatment at fillet weld toe region even if it had defect perpendicular to the load direction (about 0.2-4 mm) at root region and suffered a root failure. And the fatigue strength seemed to be apt to decrease with an increasing root defect size. (2) The reason that fatigue strength in root failure at root where stress concentration factor is higher than that at toe is generally higher than fatigue strength in toe failure at toe where stress concentration factor is lower than that at root seems to lie in the difference of crack growth rate between the two regions. (3) As the stress concentration factor at the root of a complete penetrated fillet welded joint below 1.0 and even when the stress concentration factor at toe region was decreased by applying TIG treatment to toe region, it was about 1.5 at the best, it was likely that a fatigue failure of the joint occurred at toe region and the limit of improvement on the fatigue strength was about 1.6-2 times as large as that of a joint as welded. (4) From the results of FEM analyses, it is considered that if the root defect size can be limited to a value lower than 0.2 mm, the fatigue strength of the fillet joint can be improved to. 1.6-2 times that of a joint as welded without occurrence of a root failure by applying TIG treatment to toe region.
Discussion has been made on the influence of strain hardenability of structural steels on the resistance to brittle fracture initiation. Two high strength steels, YR90 steel and YR70 steel, with different strain hardening properties but with the same chemical composition were tested by 3-point bend CTOD method. The yield-to-tensile strength ratio, YR, for these steels are about 90% and 70%, respectively. The critical CTOD value of YR90 steel at the onset of cleavage fracture without appreciable crack growth was apparently lower than that of YR70 steel. This was addressed by 3-dimensional FE-analysis on the stress distribution in the vicinity of the crack tip. YR90 steel exhibits more elevated crack tip stress and larger extent of highly stressed region than YR70 steel, which leads to lower resistance to cleavage crack initiation. FE-analysis indicated that the near-crack tip stress intensity is controlled by the strain hardening exponent n rather than by the yield ratio YR. The larger the strain hardening exponent n, the more the near-tip stress increases. This implies that the material with a larger n should retain more redundant fracture toughness for assuring structural integrity.
This study was aimed at development of a fabrication process of Functionally Gradient Material (FGM), consisting of NiCr and YSZ, made by using Low Pressure Plasma Spraying. Our research showed that the density of coatings largely depended on the pressure, substrate position and particle size during spraying. And studies were carried out on the microstructure of FGM compared with NiCr and YSZ monotonunous coatings. In the case of a NiCr monotonous coating and YSZ monotonous coating, the microstructures of particles were of a columnear type. The direction of grain growth was perpendicular to the surface of the coating. On the other hand, in the case of FGM, the microstructure of NiCr was of an equiaxed type. In this case, the deposited and solidified NiCr particles were considered to be remelted again by the molten YSZ particles, which impinged on these NiCr particles and to solidify at a relatively slow rate. Additionally, investigation of the interface between Cu substrate and coating, and also between particles was carried out in an atomic scale. The results showed that the interface was formed by either a thin oxide amorpous composite layer or a coherently connected crystal plane boundary.
In recent years, resistance reflow-soldering method has been applied to the connection between solder-plated PCB (printed circuit board) and thin insulated wire to allow high-density assembling of high-perfomance electronics equipument. Extensive investigation of reflow conditions, and evaluation of strength and reliabilty of the microconnection are required because the wire is soldered without physically removing the insulation. (1) Quick heating and quick cooling, less than 0.3 s, is the key in realizing ideal microconnection, with the insulation thermally removed. (2) Realizing qiuck heating and cooling requires a tip contact pressure of 800N/cm2 (weight : 2N) and a proper amount of solder on the pad. The result of our evaluation of field sample boards indicates that the microconnections which were soldered by this soldering method did not age even after 10 years of field operation.