In this study, to consider a method for the prevention of the cracks occuring in ceramics on the solid state diffusion bonding of ceramics and metals, the modeling is done and the thermal elasto-plastic analysis is carried out. From the results, the characteristics of residual deformation and stress produced by the solid state diffusion bonding and its production mechanism are elucidated. It is also found that the main mechanical factor of the cracks occuring in ceramics is bending moment acting upon the ceramics which is caused by the difference of shrinkage between ceramics and metals. Therefore, it is considered that the bending moment acting upon the ceramic should be as small as possible for prevention of the cracks occuring in ceramics. From this point of view, the validity of small bending moment acting upon the ceramic is concretely shown. Moreover, the mechanical significance of the test specimen for the evaluation of bonding strength of ceramics and metals is elucidated.
Hot isostatic pressing (HIP) of powders is a manufacturing process which forms high quality components from ceramic and metal powders under the condition at high temperature and high pressure. The most important problem for the HIP process is to get uniformly densified near-net-shape products. Because the sintering behavior during HIP depends on many process parameters, a simple and systematic method is greatly required to select the optimum process variables without trial and error procedures. In this paper, analytical formulation for an axially symmetrical model is presented to predict the sintering deformation behavior during hot isostatic pressing of cylindrical bodies. The governing equations consist of three parts: heat conduction equation, densification rate equation and shape change equation. Effects of particle radius, HIP temperature, pressure and initial density distribution are discussed on the results of computer simulation of alumina powders.
Melting process and spiking phenomenon have been investigated in electron beam welding. X-rays generated as a consequence of beam-metal interaction were measured at some specific sites of 3 mm in length along penetration using Xe-proportional counter simultaneously with taking highspeed photography of the molten metal flow to clarify a melting process. The results obtained were as follows. (1) Spiking phenomenon was most likely to occur when the electron beam .was focussed on the root portion of penetration. (2) Melting process and spiking phenomenon were dominated by the periodical flow of the molten metal. (3) Soon after the periodical ejection of the molten metal, the beam cavity was clear of the molten metal and the electron beam was free to drill the bottom causing the spike. (4) it is effective in monitoring spiking phenomenon to detect electrons emitted from interacting point using a probe biased 6V with respect to the specimen.
Liquid phase diffusion bonding in which a liquid phase is formed by the reaction diffusion between insert and base metals has been studied. Ag was adopted as the insert metal and Cu was used as the base metal for simplicity. The growth process of the liquid phase along the laying surface was investigated. Bonding tests were performed in a vacuum environment of the order of 10-4Pa at the bonding temperatures T=1053 to 1093K and at the bonding pressure P=3MPa. In the reaction diffusion acorss the interface full contacted by cold-pressure welding of Cu to Ag sheet, the width of the liquid layer is in proportion to the square root of the holding time. On the other hand, In the actual diffusion bonding, it is shown that there exists an apparent incubation period for the liquid-layer growth at the early stage of bonding. The liquid-spreading behaviour in the incubation period was examined. As a result, it is found that the liquid spreading process on the faying surface is achieved by three mechanisms, i.e., (1) the break-up of oxide film by the plastic flow and the reaction diffusion between insert and base metals, (2) the reaction diffusion across the exide film, and (3) the permeating operation between the faying surface and the liquid phase.
Three sorts of amorphous metal foil, Fe-Co-Si-B, Fe-Ni-Mo-B and Co-Fe-Ni-Mo-Si-B alloys, were spot-welded by using a stored energy spot welding machine, and examined the tensile shear strength of their single and multiple spot welds. The former two specimen foils showed insufficient joint strength and fracture occurred at the inside of the weld nugget. The third one showed higher joint strength than the former two and a crack formed at the periphery of the weld nugget and extended into base metal. Tensile shear strength of multiple spot welds increased with the increase in the number of weld nugget in their own ways. Multiple spot weld of the third foil showed good ductility in bending with tensile shear loading. X-ray diffraction patterns from the weld nuggets of the former two foils had some peaks indicating crystallization, while the pattern from the third one had only a broad peak. Both weld nugget thickness and electrode force had not the influence for the prevention of crystallization of the weld nugget in the range of this experimental conditions. Weldability of amorphous metal foil for stored energy spot welding was not affected by iron content in the foil, but mainly dominated by its chemical constituent.
A new type of solid state welding has been developed. In this method named "Twist compression welding", surface oxide films are effectively broken and removed from the interface because a pair of specimens are mutually twisted under compression load, resulting in the direct contact between metal matrices. It is found that the method can successfully be applied to the joining of commercial purity aluminum JIS A 1050 almost independent of the surface roughness as well as of the oxide film thickness.
Mechanical properties of work hardened pure titanium joint brazed with Ti-Cu-Cr-Al filler metal were investigated. Test specimens were brazed with filler metal containing 29%Ti, 62.5%Cu, 6.5%Cr and 2%Al in a vacuum. Brazing temperature were 850°C, 900°C, 1, 000°C and 1, 100°C for 10sec. Tensile strength of butt joints were comparable to that of joints brazed with conventional Ti-Ni-Cu filler metal, and hardness at the joint was lower. The reaction of filler metal with base metal was modertely and damage of base metals were less. The addition of pressure to joint during brazing gave significant effect on joint strength.
Vacuum brazing is very useful for joining materials that are difficult to join by fusion welding and other techniques. A major problem associated with vacuum brazing, however, is how to select proper brazing alloys and joining procedures most suitable for a given joining task. The objective of this research was to solve some of this problem by devoloping a computer-aided system for selecting proper brazing materials and recommended procedures for a variety of joining tasks by utilizing: (a) Experience of vacuum brazing in own laboratory (b) Existing data available in published literature (c) Data on chemical reactions between elements of brazing alloys and materials to be joined The authors developed the algorithm to select proper brazing alloys based on these informations. Therefore, the developed system can show the candidate brazing alloys, even for unexperienced materials to be joined. The programs have been written in COMMON LISP, therfore software can be used with minimum modifications on any computer as long as COMMON LISP can be used. The developed system will be improved by the authors basis on the experience of using this system.
Three kinds of Fe-Cr-Ni ternary alloys were surface-melted by a CO2 laser and effects of rapid solidification on solidification modes and microstructures were investigated. It was found that characteristic rod-like eutectic structure formed in these alloys rapidly solidified by laser surface melting which could not be seen in conventional TIG weld metals. The rod-like eutectic structure almost formed in the limited compositional range with iron content of more than 57% in which primary ferrite solidification occurred in conventional TIG weld metals. It was also seen that the formation tendency of the rod-like eutectic structure first increased and then decreased with increasing laser traveling velocity. Austenite in the rod-like eutectic structure was a rod-like in shape and orientation relationship of ‹100› δ// ‹100› γ was confirmed between austenite and ferrite. STEM analysis revealed that element distributuin across austenite and ferrite was not so largely changed in the rod-like eutectic structure comparing with that in vermicular ferrite structure in the TIG weld metal.
By investigation of effects of rapid solidification by laser surface melting (LSM) on solidification modes and microstructures of stainless steels, it was found that characteristic massively solidified structure formed in laser surface melted specimens of a certain compositional range which could not be seen in conventional TIC weld metal. In the massively solidified structure it was seen that a certain orientation relationship between austenite and bulky ferrte did not exist. STEM analysis had revealed that no differences of compositions between austeinte and ferrite of this structure. The massively solidified structure only formed when cooling rate was reaching a certain critical value a limited compositional range. The critical cooling rate for massive solidification depended strongly on compositions of alloys and it was found that this critical cooling rate became larger with increasing the Creq/Nieq of alloys for the same iron content. From examination of mechanism of massive solidification, it was shown that massive solidification would be formed when maximum growth velocity of dendrite was slower than isotherm velocity and large supercooling took place in the liquid ahead of growing dendrite.
The clad steels are often produced by hot roll bonding with an insert of nickel. The influences of inter-diffusion between nickel and carbon steel on the microstructure and properties at the bonding interface were studied by means of the hot compressive bonding test. The hard layer formed at the bonding interface of steel/nickel held at 923K after heated to 1523K for 10ks, where the high carbon martensite phase was observed. At the bonding interface, the nickel diffused into the carbon steel side and the ferrite transformation temperature in the nickel diffused steel was lower than that in the base metal. The formation mechanism of carbon concentrated layer at the bonding interface can be explained by the carbon diffusion which is driven by the ferrite transformation temperature difference between in the base metal and the nickel diffused region.
Effects of solution treatment temperature and sensitization time on stress corrosion cracking (SCC) have been studies on SUS316 stainless steel in high temperature pure water at 562K containing dissolved oxygen of 8 ppm using a slow strain rate testing (SSRT) technique at 4.17x10-6s-1 and 8.35×10-7s-1. The Strauss test (ASTM A262E) and the oxalic acid etching test (ASTM A262A) were used to determine the degree of sensitization and Huey test (ASTM A262C) and anodic polarization test were used to determine the influence of step solution treatment on segregation of impurities at grain boundary. The specimens which were solution-treated at 1373K, had more precipitates of M23C6 and Laves phases than those at 1573K. For the width of attacked grain boundaries, this trend was coincident. In high temperature water, intergranular corrosion occurred owing to Cr depletion resulting from the precipitation of M23C6 and Laves phase at grain boundaries of sensitized specimens and then IGSCC occurred at these attacked grain boundaries at low strain and load. IGSCC changed to TGSCC according to the increase of strain.
Effect of P content on stress corrosion cracking (SCC) has been studied for SUS304 stainless steel in high temperature water at 562K. SCC test was carried out using slow strain rate testing (SSRT) technique at 4.17×10-6s-1. For the solution-treated specimens with 0.008%P to 0.10%P, the corrosion rate by Huey test increased with increasing P content, and that correlated with segregation of P at the grain boundaries. But, intergranular stress corrosion cracking (IGSCC) hardly occured. The precipitation of M23C6 by sensitization treatment at 723K increased with increasing P content, Because it is considered that phosphorus was inserted in the M23C6, and carbides precipitated as M23(C, P)6. IGSCC in high temperature water increased with increasing P content, because of the increase of M23(C, P)6 at the grain boundary. The specimens sensitized after solution treatment at 1373K occured IGSCC more than that at 1573 K, because of the increase of M23(C, P)6 at the grain boundary.
Role of Niobium on stress corrosion cracking (SCC) of SUS347 stainless steel was investigated in high temperature water at 562K. SCC test was carried out using a slow strain rate testing technique (SSRT) in dissslved oxygen of 8 ppm. The precipitation behavior of NbC and M23C6 was evaluated by transmission electron microscopy and intergranular corrosion test. All the specimens were firstly stabilized at 1173K for 3.6ks, in order to precipitate more NbC in the specimen. The specimen was solutionized at 1273K to 1573K for 1.8ks, and then sensitized at 923K for 72ks. The solution-treated specimen up to 1273K occured general corrosion and had low pitting potential, and SCC in the high temperature water hardly occured, because of the presence of NbC. The amount of NbC decreased with increasing solution treatment temperature in the range of 1473 K to 1573K. M23C6 precipitated at the grain boundary, and intergranular corrosion occured by the sensitization treatment at 923K. The intergranular stress corrosion cracking (IGSCC) occured in the range above 1473K, because of the precipitation of M23C6 at the grain boundary.
Several cases of cracking failures in the HAZ of alloy 800H pipe have been experienced in equipment operating in the temperature range of 550-700°C. The influence of several heat treatments on the cracking sensitivity by cylindrical type restraint cracking test was investigated. And the mechanism of this crack formation was considered. Main results obtained in this research were as follows. (1) Intergranular oixidation and cracking were detected at the bottom of notched HAZ area of as-welded specimens in the temperature range of 600-650°C. The area of cracking coincided with the area of γ' phase precipitation. (2) By PWHT of solution heat treatment, HAZ cracking was not detected in the specimens aged for 3000 hours at 600°C, while only intergranular oxidation was detected. The sensitivity of this cracking can be reduced remarkably by the use of the PWHT of solution heat treatment that reduces the initial weld residual stress. (3) When the cohesive force between grain boundaries is severely reduced by intergranular oxidation and weld tensile residual stress acts upon grain boundaries, the intergranular cracking occurs.
Considerable reports concerned with stress and strain near a crack in the residual stress field have been published. In some of those reports, however, the redistribution of residual stress after a crack growth was not taken into account. In the present study, a butt welded plate with a through-thickness crack is dealt with. Uniform tensile load perpendicular to the crack which initiates after welding is applied to the plate. Stress, strain, plastic zone near a crack and crack opening displacement are examined by elasto-plastic finite element analysis as well as experiment. The residual stress is considered in the analysis. The residual stress and its redistribution after crack growth are measured by means of the ultrasonic stress measurement technique, because, from a practical point of view, the stress measurement needs to be nondestructive. The effect of residual stress on the deformation near a crack is revealed. The tensile residual stress around a crack tip contributes to the decrease of fracture strength at both low-applied-stress level and high-applied-stress level. On the other hand, the compressive residual stress around a crack tip contributes to the increase of fracture strength at high-applied-stress level.
In this study, local explosive treatment was used for the reduction of residual stress of weld joint and the effect of factor (type of explosive, quantity of explosive and the order of explosive treatment) on reduction of residual stress was investigated. When the surface and backface of weld joint were treated at the same time with 6 detonating cords, the tensile residual stress of weld metal and HAZ in weld joint decreased from 400 MPa-300 MPa in the case of as-welded condition to 200 MPa-100 MPa. Especially with dynamite, the residual stresses decreased to ±30 MPa.
The final purpose of our study is to discuss the selection of surface modification processes and/or materials from a viewpoint of blast erosion properties. In this study, an experimental investigation was carried out on the blast erosion resistance of thermal sprayed metal coatings. Eight different coatings of 18Cr-8Ni steel, 13Cr steel, Cu, Co base alloy and Cu-Ni alloy, which were produced by FLSP, EASP and PSP, were examined in comparison with substrate. materials. The effect of test conditions, such as blast angle, blast particle size and air pressure, on the erosion resistance were made clear. The better correlation between volume erosion rate and Vickers hardness after erosion could not be obtained from the experimental results. It appears that the volume erosion rate of coatings may be extremely affected by spraying conditions in the case of same materials. It was also confirmed by experiments that the volume erosion rate of 18Cr-8Ni steel coatings could be improved by heat treatment (600°C, lhr) for stress relief and phase stabilization.
This study has been carried out to develop new cathode materials for air-plasma cutting. The consumption of Re-Y2O3 and Ru-Y2O3 electrodes was compared with that of Elf and Zr electrodes which have been widely used. Electrodes of Re including 15 to 40% Y2O3 and Ru including 10 to 35% Y2O3 showed lower rates of consumption rather than those of Hf and Zr electrodes in case of continuous life time test. Furthermore, 85Ru-15Y2O3 electrode showed a superior erosion resistance in case of periodic operating test at 25 A compared with the other electrodes.
A reactive bonding method of Cu foil to sintered SiC ceramics using Cu-Mn liquid insert alloy was reported previously (Report 1). Solid-state and liquid-state reactions of Cu-Mn/SiC were investigated in this report at heating temperatures of 500-700°C for 1 min and 900°C for-60 min using EPMA, AES and XRD. Results obtained are summarized as follows. 1) Mn concentrates to the Cu-Mn/SiC interface at heating above 600°C (Cu-Mn is in solid state). Depth profile analysis with AES revealed that Mn reacts to SiC and releases the C, forming Mn-silicides such as Mn5Si3 and Mn5Si2. While the released C diffuses into the Mn layer. 2) Any reaction layer, except C rich layer, couldnt be observed at liquid Cu-Mn/SiC interface by heating even at a high temperature for long time (900°C, 60 min). But a phenomenon of separating and flouting into the liquid of sintered SiC grains was observed, which is considered to be caused by the preferential diffusion of Mn into grain-boundarys of sintered SiC.