Search

This study investigated the effect of the hydrogen charging time on the hydrogen embrittlement of hot-rolled and accelerated-cooling treated API X70 steel by using the electrochemical hydrogen charging method. Tensile and V-notch Charpy impact test were completed for the specimens of hydrogen charged for 0, 2, 4, and 10 h, and then microstructural observation were performed. The tensile and yield strength tended to decrease slightly and the total elongation started to decrease rapidly up to 2 h charging time and then these gradually decreased with the hydrogen charging time. The post-uniform elongation increased slightly after the holding time of 2 h due to the occurrence of two-step stress reduction phenomenon and its mechanism has suggested. The effect of the hydrogen embrittlement on impact absorption energy according to the hydrogen charging time were also investigated. The fracture surface of the hydrogen charged ones are generally composed of cleavage fracture surfaces. It was demonstrated that the external cracks were formed on the outside of tensile tested specimen and the external shape of the fracture portion was fractured without large elongation at hydrogen charged specimens.

The manufacturing process of large scaled Al 7050 alloy is difficult for the occurrence of solidification crack during casting. The aims of this study are the evaluations of microstructure and mechanical properties of extruded Al 7050 billet and ring forged one with large scale. Large scaled Al 7050 billet was casted by direct-chill casting process. The extruded and ring forged specimens were prepared from the casted ingot after residual stress relief and homogenization heat treatment, respectively. Microstructures, hardness and tensile test of the surface, middle and center part of each specimen were performed at room temperature. Sheared and elongated type grains were observed at the edge parts of surface and center area and its aspect ratios of grains were low and similar as 0.21 while that of middle area was closed to 0.92 value in ring forged Al 7050 alloy. The mechanical properties of extruded Al 7050 alloy were superior than those of ring forged one. The hardness values of surface and center part were slightly higher than that of middle part in ring forged Al 7050 alloy.

Caused corrosion by hydrogen on stainless steel using nondestructive technique is one of issues to be clarified in nuclear fusion industry. In this study, an ultrasonic wave was used to evaluate the degree of corrosion by hydrogen charging of stainless steel. The mechanical properties of hydrogen charged material including tensile strength and strain were discussed, and the change of surface of specimen according to the hydrogen charging quantities was observed. The relationship between fractography and ultrasonic wave characteristics on hydrogen charged material discussed. In addition, acoustic emission technique was applied to clarify the dynamic behavior such as dislocation, deformation and crack in material by loading. AE parameters of event, energy, amplitude and frequency were analyzed according to the degree of load, and optical AE parameter was derived to evaluate the degree of the damage of hydrogen charged stainless steel.

The aim of the present study is to identify the properties of intermediate phases formed on the bonding interface of hot pressed Cu/Al clad materials by transmission electron microscopy and nano-indentation analyses. Cu/Al clad materials were fabricated by hot pressing under 200 MPa at 250 °C for 1 h and then heat treated at 400 °C for 1 h. Nano-indentation measurement was conducted to evaluate the nanohardness and modulus of the intermediate phases formed between the Cu/Al interfaces. A 3-tier diffusion layer was observed at the Cu/Al interfaces. Knoop microhardness values at the bonding interface were 7 to 11 times that of the Cu and Al matrix metals. The intermediate phases formed at the bonding interface were Al4Cu9, AlCu, and Al2Cu. A mapping analysis confirmed that the Al and Cu particles moved via mutual diffusion toward the intermediate phases formed at the bonding interface. The nanohardness values of η2-AlCu and γ1-Al4Cu9 were 4 to 7 times that of the Cu and Al matrix metals. Nanohardness and Knoop microhardness measurement curves exhibited similar tendencies. The rigidity values of the respective intermediate phases can be arranged in descending order as follows: γ1-Al4Cu9 > η2-AlCu > θ-Al2Cu.

A stainless steel material is used as components for storing hydrogen gas and liquid hydrogen, or for transportation raw material and oil in storage container. Brittle fracture associated with hydrogen is observed for stainless steel and these phenomena of hydrogen embrittlement were very important for wide-ranging application of stainless steel. Many researchers have studied the hydrogen embrittlement from the mechanical and metallographic point of views. The aim of this study is to identify the material degradation by hydrogen embrittlement for 316L stainless steel using nondestructive evaluation. That is, the relationship between the mechanical properties of 316L stainless steel by hydrogen charging and nondestructive technique of acoustic emission technique and an ultrasonic wave is to be clarified. The relationship between fractography and ultrasonic wave characteristics on hydrogen charged material for 0hr and 24hr was discussed. SEM and optical microscope were used to inspect the fracture surface of hydrogen charged material. The fracture surface of the charged specimen became brittle, especially on the surface nearby. AE parameters of event, count, energy, amplitude and frequency were analyzed according to the degree of the damage of hydrogen charged stainless steel.

This study was carried out to observe and measure the microstructure, distance between dendrite arms, aspect ratio, and Knoop hardness change of extruded material formed by the hydro co-extrusion of Al3003/Al4004 clad material manufactured by the duo-casting method. The specimen of duo-casted Al3003/Al4004 clad materials was circle shaped, it was composed of Al3003 (outside) and Al4004 (inside) materials. The manufacturing conditions of the hydro co-extruded specimen were 423 K temperature and 6.5 ratio of extrusion. At the interface of the duo-casted Al3003/Al4004 clad material, a non-junction at the interface and non-metallic inclusions of Si- and Mn-based oxides were observed. Al3003 exhibits equiaxed crystals, Al4004 has a casted structure with dendrites before extrusion, showed slight deformation during extrusion, and then finally exhibited completely deformed structures after extrusion. In the cast material, the distance between dendrite arms increased, and the aspect ratio of dendrites tended to decrease from the surface to the center. However, in the case of the extruded material, neither Al3003 nor Al4004 changed significantly from the surface to the inside. As extrusion progressed, the Knoop hardness value at the interface of Al3003/Al4004 increased rapidly compared with those of Al3003 and Al4004 matrixes.

Embrittlement of material by hydrogen charging should be cleared for safety of storage vessel of hydrogen and components deal with hydrogen. A stainless steel is generally used as materials for hydrogen transportation and storage, and it has a big advantage of corrosion resistance due to nickel component in material. In this study, microscopic damage behavior of stainless steel according to the hydrogen charging time using nondestructive evaluation was studied. The surface of stainless steel became more brittle as the hydrogen charging time increased. The parameters of nondestructive evaluation were also changed with the embrittlement of stainless steel surface by hydrogen charging. Ultrasonic test, which is the most generalized nondestructive technique, was applied to evaluate the relationship between the ultrasonic wave and mechanical properties of stainless steel by hydrogen charging. The attenuation coefficient of ultrasonic wave was increased with hydrogen charging time because of surface embrittlement of stainless steel. In addition, acoustic emission test was also used to study the dynamic behavior of stainless steel experienced hydrogen charging. AE event at the hydrogen charged specimen was obviously decreased at the plastic zone of stress-strain curves, while the number of event for the specimen of hydrogen free was dramatically generated when compared with the specimens underwent hydrogen charging.

The effects of hydrogen charging on the mechanical properties of 304 stainless steels were investigated in conjunction with the detailed examinations of their fracture modes. The dependence of the absorbed impact energy and the surface hardness of the 304 stainless steels on the hydrogen charging time was characterized. The tensile properties of the 304 stainless steels by the variation of cross-head speed were also evaluated at the room temperature. The hydrogen charging was performed by an electrolysis method for all specimens of the 304 stainless steels. The mechanical properties of the 304 stainless steels exhibited the sensitivity of embrittlement due to a hydrogen charging. The correlation between mechanical properties and fracture surfaces was discussed.

This paper dealt with the interfacial bonding properties of Cu/Al clad materials by the variation of aging treatment times. Cu/Al clad materials were fabricated by a hot-pressing process. A subsequent heat treatment was also performed for the interfacial strengthening of Cu/Al clad materials. The characterization of Cu/Al clad materials was evaluated by means of OM, SEM, EDX and Knoop hardness test. Several diffusional layers were created at the interfacial region of Cu/Al clad materials, due to the chemical reaction of Cu and Al elements. The thicknesses of interfacial diffusion layers for Cu/Al clad materials increased with the increase of aging treatment time, accompanying the variation of intermetallic compounds. The hardness strengthening of diffusion layers by the increase of aging treatment time was also affected by the formation of η2 phase at the bonding interfacial region.

The objective of this study is to evaluate the elastic wave's characteristic on the crack in the weld of stainless steel materials using guided wave and acoustic emission, nondestructive tests. The stainless steel is expected as candidate of structural piping material under high temperature condition in nuclear fusion instrument, and a tungsten inert gas (TIG) weld technique was applied for making its jointing. The defect size of 20 mm was induced in the weld material. The guided wave, one of elastic waves, can propagate through very long pipe, and easily change to lots of modes by the defects in the structure. By analyzing the relationship between the mode conversion and the defects we can evaluate existing of the defects in weld material. In present study Nd-YAG laser was used to excite the guided wave by non-contact method, and AE technique was also used to clarify the mode conversion of guided wave by defect because lots of AE parameters of energy, count and amplitude can give more chances for analysis of mode conversion. The optimal AE parameters for the evaluation of the defects in weld zone using laser guided wave were derived.

During the use of API X70 steel as a pipeline structural material for the transportation of natural gas, hydrogen embrittlement can occur due to the hydrogen contained in natural gas. The aim of this study is to investigate the effects of the hydrogen content under high-pressure hydrogen gas conditions on the hydrogen embrittlement of air-cooled API X70 steel. The air-cooled API X70 steel was manufactured by hot rolling and was then air-cooled to room temperature. Tensile test specimens were held for 0 h, 1000 h, and 2000 h within a pressure vessel filled with 100% hydrogen gas at a gas pressure of 10 MPa, with the tensile tests then performed at room temperature. The microstructure of the API X70 steel consists of coarse polygonal ferrite, coarse pearlite, and fine acicular ferrite. The yield and tensile strength increased and elongation decreased considerably after a holding time of 2000 h compared to those of 0 h and 1000 h within the pressure vessel. The morphology of the fracture surface changed from ductile to brittle upon hydrogen gas charging. Secondary cracks were observed in both of the hydrogen-gas-charged specimens. No external cracks were formed on the surface of the tensile-tested specimen with a 0 h holding time; however, many external cracks were observed on the specimen surface subjected to hydrogen gas charging.

The effects of hydro co-extrusion on the microstructure changes of aluminum hybrid duo-cast Al 3003/Al 4004 clad materials were studied. The specimen of duo-cast Al 3003/Al 4004 clad materials was in circle shape, and was composed of Al 3003(outside) and Al 4004(inside) materials. The specimen was extruded by the hydro co-extrusion equipment. The manufacturing conditions of the specimen were 423 K in temperature and 5 in extrusion ratio. The dimensions of the specimen were 80 mm in diameter of the Al 4004 material and 35 mm in thickness of the Al 3003 material before the hydro co-extrusion process, and 30 mm in diameter and about 5 mm in thickness after the extrusion process, respectively. The microstructure and the hardness for two specimens were investigated. The hardness value of cross section in the duo-cast Al 3003/Al 4004 clad materials before the extrusion process was increased in form of the parabola toward the center. However, after the extrusion process, it was almost constant in the portion of Al 4004 material. Lots of big voids above 1 mm in diameter in the specimen existed in the interfacing region of Al 3003 and Al 4004 materials before the extrusion process. These big voids disappeared after the process of hydro co-extrusion.

The objective of this research is to study the effect of various hydrogen charging quantities in austenitic stainless steel using nondestructive technique. The hydrogen charging equipment was designed to make charging the steel, and the specimens were charged for 2, 4, 10 and 24 hours in the equipment. An acoustic emission (AE) technique, nondestructive test, was used to evaluate the dynamic behavior of the hydrogen charged austenitic stainless steel specimen. The tensile load was applied the charged specimen with the attached AE sensor, and elastic waves caused plastic deformation and cracking in the specimen by external tensile loading were caught at the AE sensor and analyzed by the AE parameters such as count, energy, duration time, event and amplitude. In addition, ultrasonic wave was also used to evaluate the degree of hydrogen charging. The velocity and the attenuation ratio of the ultrasonic wave on the specimen with different hydrogen charging conditions were measured. The velocity was not changed but the attenuation ratio was linearly increased with the hydrogen charging time. The relationship between the results of nondestructive test including AE test and ultrasonic test and fractographic analysis by using SEM was discussed.

Aluminum clad steel (ACS) is an excellent layered composite material. An intensive investigation into roll-bonded ACS was carried out to identify the intermetallic compound (IMC) formed at the interface between the aluminum (Al) and the steel. A series of analyzing methods was applied to the IMC layer formed at the interface during annealing at 540 °C for 16 h. An electron probe micro-analyzer (EPMA) measured a value of 28.5 atomic percent for the Fe in the IMC layer, which coincided with the Fe2Al5 phase. An analysis of the X-ray diffraction pattern for the IMC layer in the ACS materials showed a very strong peak for the (002) plane of Fe2Al5. Vickers microhardness testing of the IMC layer revealed a very high value (1,110 Hv). The results of EPMA, XRD and microhardness values verified that the IMC layer in the sample that had been annealed at 540 °C for 16 h was the Fe2Al5 phase.

A TIG welded 316 stainless steel materials will have a large impact on the design and the maintenance of invessel components including pipes used in a nuclear power plant, and it is important to clear the dynamic behavior in the weld part of stainless steel. Therefore, nondestructive techniques of acoustic emission (AE) and ultrasonic wave were applied to investigate the damage behavior of welded stainless steel. The velocity and attenuation ratio of the ultrasonic wave at each zone were measured, and a 10 MHz sensor was used. We investigated the relationship between dynamic behavior and AE parameters analysis and derived the optimum parameters to evaluate the damage degree of the specimen. By measuring the velocity and the attenuation of an ultrasonic wave propagating each zone of the welded stainless steel, the relation of the ultrasonic wave and metal structure at the base metal, heat affected zone (HAZ) metal and weld metal is also discussed. The generating tendency of cumulated counts is similar to that of the load curve. The attenuation ratios from the ultrasonic test results were 0.2 dB/mm at the base zone, and 0.52 dB/mm and 0.61 dB/mm at the HAZ zone and weld zone, respectively.

Cu/Al bar clad material was fabricated by a drawing process and a subsequent heat treatment. During these processes, intermetallic compounds have been formed at the interface of Cu/Al and have affected its bonding property. Microstructures of Cu/Al interfaces were observed by OM, SEM and EDX Analyser in order to investigate the bonding properties of the material. According to the microstructure a series of diffusion layers were observed at the interface and the thicknesses of diffusion layers have increased with aging time as a result of the diffusion bonding. The interfaces were composed of 3-ply diffusion layers and their compositions were changed with aging time at 400 °C. These compositional compounds were revealed to be η2, (θ+η2), (α+θ) intermetallic phases. It is evident from V-notch impact tests that the growth of the brittle diffusion layers with the increasing aging time directly influenced delamination distance between the Cu sleeve and the Al core. It is suggested that the proper holding time at 400 °C for aging as post heat treatment of a drawn Cu/Al bar clad material would be within 1 h.

In this study, a Hydro Co-Extrusion Process of Al-Mn/Al-Si hybrid alloys prepared by electromagnetic duo-casting was investigated. Sleeve of the duo-casted billets is 3003 Al-Mn alloy and core is 4004 Al-Si alloy. It is expected hydrostatic stress during the HCE process enhances formability of materials and minimize any defects in extruded billets due to different material properties between two Al alloys. The duo-casted billet was extruded at temperature of 423K and with extrusion ratio of 5. Finally, the effect of the HCE on microstructure of the billet was investigated by an optical microscope.

This paper dealt with a liquid phase sintering process for the fabrication of carbon fiber reinforced SiC matrix composites (Cf/SiC), using a ultra-fine SiC particles and oxide additive materials. Especially, the thermal shock properties of Cf/SiC composites were investigated at the elevated temperatures. The characterization of monolithic SiC materials by the variation of starting SiC particle size was also examined. Monolithic SiC materials possessed an excellent density higher than about 3.0 mg/m3 and a good flexural strength of about 700 MPa, regardless of starting SiC particle size. Cf/SiC composites also represented a dense morphology in the intra-fiber bundle region, even if there were some amount of pores. However, the flexural strength of Cf/SiC composites greatly decreased at the thermal shock temperature of 400 °C.

The effect of He-injection on irradiation-induced segregation of aging treated Fe–12%Cr–15%Mn austenitic steels, which are candidate materials as the reduced radio-activation of structure material for nuclear and/or fusion reactors was investigated by using the 1250 kV high voltage electron microscope (HVEM) connected with an ion accelerator. The Fe–Mn–Cr steel has been irradiated at 573 K by three irradiation modes of single electron-beam irradiation, electron-beam irradiation after He-injection and electron/He+-ion dual-beam irradiation in a HVEM. Irradiation-induced segregation analyses were carried out by an energy dispersive X-ray analyzer (EDX) in a 200 kV FE-TEM with beam diameter of about 0.5 nm. Dislocation loops with strain contrast were formed during irradiation and the loop numbers density increased rapidly with irradiation dose for He-pre-injected specimens. Voids were not observed after irradiations with three irradiation modes up to 5.4 dpa at 573 K. Irradiation-induced segregations of Cr and Mn near grain boundary were observed in each irradiation condition, but the amounts of Mn segregation decreased in the cases of electron/He+-ion dual-beam irradiation compared with single electron-beam and electron-beam irradiation after He-injection conditions.

This paper dealt with the thermal shock properties of SiCf/SiC composites reinforced with two dimensional SiC fabrics. SiCf/SiC composites were fabricated by a liquid phase sintering process, using a commercial nano-size SiC powder and oxide additive materials. An Al2O3–Y2O3–SiO2 powder mixture was used as a sintering additive for the consolidation of SiC matrix region. In this composite system, Tyranno SA SiC fabrics were also utilized as a reinforcing material. The thermal shock test for SiCf/SiC composites was carried out at the elevated temperature. Both mechanical strength and microstructure of SiCf/SiC composites were investigated by means of optical microscopy, SEM and three point bending test. SiCf/SiC composites represented a dense morphology with a porosity of about 8.2% and a flexural strength of about 160 MPs. The characterization of SiCf/SiC composites was greatly affected by the history of cyclic thermal shock. Especially, SiCf/SiC composites represented a reduction of flexural strength at the thermal shock temperature difference higher than 800 °C.

The abrasive wear patterns and the tensile properties of steel saw wires (120 μm in diameter) were investigated in order to develop highly reliable saw wires for the application to silicon (Si) ingot slicing. Saw wires that underwent heat treatment at different linear velocities during the patenting process were subjected to 2-body abrasive wear (2-BAW) and 3-body abrasive wear (3-BAW) tests. The 2-BAW and 3-BAW tests of the saw wires showed opposite trends in abrasive wear resistance. The wear loss resulting from the 2-BAW test was mainly determined by the tensile strength and microhardness of the steel saw wire samples, while the wear loss from the 3-BAW test was primarily determined by the elongation, or ductility, of the samples.

This paper dealt with the microstructure and mechanical properties of SiC based composites reinforced with different reinforcing materials. The composites were fabricated using reinforcing materials of carbon nanotubes (CNT) and Tyranno Lox-M SiC chopped fibers. The volume fraction of carbon nanotubes was also varied in this composite system. An Al2O3–Y2O3 powder mixture was used as a sintering additive in the consolidation of the SiC matrix. The characterization of the composites was investigated by means of SEM and three point bending tests. These composites showed a dense morphology of the matrix region, by the creation of a secondary phase. The composites reinforced with SiC chopped fibers possessed a flexural strength of about 400 MPa at room temperature. The flexural strength of the carbon nanotubes composites had a tendency to decrease with increased volume fraction of the reinforcing material.

The flexural strength of based composites reinforced with Nb sheets has been investigated, based on the detailed examination of their microstructure and fractured surface. Both sintered density and porosity of Nb/ composites were also examined. Nb/ composites were fabricated by different conditions such as temperature, applied pressure and its holding time, using a hot-press device. The volume fraction of Nb sheet in this composite system was fixed as 10%. The characterization of Nb/ composites were investigated by means of optical microscopy, scanning electron microscope and three point bending test. Nb/ composites represented a dense morphology at the interfacial region, accompanying the creation of two types of reaction layer by the chemical reaction of Nb and . Nb/ composites possessed an excellent density at the fabricating temperature of , corresponded to about 95% of theoretical density. The flexural strength of Nb/ romposites were greatly affected by the pressure holding time at the same fabricating temperature, owing to the large suppression of porosity in the microstructure. Especially, Nb/ composites represented a good flexural strength of about 310 MPa at the fabricating condition of , 30MPa and 60min, accompanying the pseudo-ductile fracture behavior by the deformation of Nb sheet and the interfacial delamination.

The aim of the present study is to derive optimized post heat treatment temperatures to get a proper formability for Ti/STS409L/Ti clad materials. These clad materials were fabricated by cold rolling followed by a post heat treatment process for 10 minutes at temperatures ranging from 500℃ to 850℃. The microstructure of the interface was observed using a Scanning Electron Microscope(SEM) and an Energy Dispersive X-ray Analyser(EDX) in order to investigate the effects of post heat treatment on the bonding properties of the Ti/STS409L/Ti clad materials. Diffusion bonding was observed at the interfaces with a diffusion layer thickness increasing with the post heat treatment temperature. The diffusion layer was composed of a type of(e + ζ) intermetallic compound containing additional elements, namely, Fe, Ti and Ni. The micro Knoop hardness of the Ti/STS409L interfaces was found to increase with heat treatment up to 800℃ and then decrease for temperatures rising up to 850℃. The tensile strength was shown to decrease for heat treatment temperature increasing to 750℃ and then increase rapidly for temperature rising up to 850℃. A post heat treatment temperature range of 700~750℃ was found to optimize the formability of Ti/STS409L/Ti clad materials.

To investigate the effect of aging treatment on irradiation-induced segregation of high Mn-Cr steel, specimens for electron-beam irradiation were prepared from the high Mn-Cr austenitic steel which was solution treated at 1 373 K for 1 h and aging treated at 573 K for 1 000 h, respectively. The electron-beam irradiation was performed at 573 K up to doses of 5.4 dpa in a 1 250 kV HVEM and irradiation-induced segregation analyses were carried out by an EDX in a 200 kV FE-TEM. The results show that void formation is not observed in both solution treated and aging treated ones. The amount of Cr segregation at the grain boundary decreases in the aged one; however, that of Mn is not changed in solution treated one.

Shape memory alloy has been used to improve the tensile strength of composite by the occurrence of compressive residual stress in matrix using its shape memory effect. In order to fabricate shape memory alloy composite, TiNi alloy fiber and Al2024 sheets were used as reinforcing material and matrix, respectively. In this study, TiNi/Al2024 shape memory alloy composite was made by using hot press method. In order to investigate bonding condition between TiNi reinforcement and Al matrix, the micro-structure of interface was observed by using optical microscope and diffusion layer of interface was measured by using Electron Probe Micro Analyser. And the mechanical properties of composite with three parameters(volume fraction of fiber, cold rolling amount and test temperature) were obtained by tensile test. The most optimum bonding condition for fabrication the TiNi/Al2024 composite material was obtained as holding for 30min. under the pressure of 60MPa at 793K. The strength of composite material increased considerably with the volume fraction of fiber up to 7.0%. And the tensile strength of this composite increased with the reduction ratio and it also depends on the volume fraction of fiber.

The long-term corrosion strength properties for the carbon steels under pressurized water atmosphere have been investigated, in the conjunction with the detailed analysis of their microstructures. The corrosion test for carbon steels was carried out at the temperature of 200°C under a water pressure of 10 MPa. The corrosion test samples were maintained up to 50 weeks in the tube shaped reactor. The mechanical strength and the microstucture of carbon steels suffered from the long term corrosion test were evaluated by SEM, XRD and tensile test. The weight loss of carbon steel by the corrosion test was also examined. The tensile strength of carbon steels decreased with the increase of corrosion time under a pressurized water atmosphere, accompanying the creation of severe corrosion damages like stress corrosion crack.

The bimetals of home appliances are mainly manufactured by cladding process and these are almost consisted with Cu alloy and Ni alloy. But it is very difficult to clad these alloys, because the brittle oxide film formed easily on Cu alloy surface during cladding process. Clad rolling and heat treatment processes were applied for the development of bimetals by using the Ni alloy and the 3 types of Cu alloys. Optical microstructure, micro-hardness, specific resistance, and deflection and line profile of newly processed bimetals specimens were observed and measured in this paper. Inter-diffusion was observed between Cu and Ni element in the interface of heat treated Cu alloy and Ni alloy clad material. The C1220 and Invar36 clad material showed the best property of deflection among the 3 kind of clad materials.

Copper/aluminum/stainless steel (Cu/Al/STS) clad materials were made by rolling and heat treatment process. These specimens were evaluated the formability and bonding strength of Cu/Al/STS clad materials. Thin disc specimens for TEM observation were prepared from the interfaces of Cu/Al and Al/STS by using the Focused Ion Beam (FIB) utility. Brittle oxide film formed on copper surface during heat treatment at 673K~773K. Diffusion bonding was observed at the interface of Cu/Al. Reacted region was formed in the interface of Al/STS with width about 10nm, while in the case of Cu/Al was formed about 1,600nm width. It was also observed nanosized crevice in reacted region of Al/STS interfaces.

The A raw C/C composite with a density of 1.40g/cm3 was used in order to investigate the high temperature erosion behavior and mechanical properties of liquid silicon infiltrated C/SiC composites. The microstructures of the as-received and infiltrated composites were examined with an optical (OM) and a scanning electron microscope (SEM). The volume fraction of residual silicon and porosity was measured by using an image analyzer. The flexural test for as-received as well as melt Si infiltrated C/C composites was performed to estimate the mechanical strength of the C/SiC composites. Severe fiber damage was occurred after infiltration. SiC was formed by reaction between carbon of fiber surface and molten Si . Flexural strength was decreased after melt Si infiltration and pull-out of fiber was observed at the fracture surface of as-received material.

The high temperature property of SiC/SiC composites fabricated by the melt infiltration (MI) process has been investigated. SiC/SiC composites reinforced with BN/SiC double coated Hi-Nicalon SiC fibers were fabricated by infiltrating molten silicon into a braiding fibric preform containing C and SiC particles. The mechanical properties of MI- SiC/SiC composites were carried out at the elevated temperatures using the three point bending test. The microstructure of MI- SiC/SiC composites was examined by means of SEM and EDS. The matrix region of MI- SiC/SiC composites represented the chemical fluctuation depending on the composition ratio of Si and C elements. The flexural strength of MI- SiC/SiC composites greatly decreased at the temperatures higher than 1100 °C, due to microstructural instabilities such as interfacial debonding and matrix oxidation.

The matrix and heat affected zone (HAZ) of welded SUS304 steel has been irradiated in an 1250 kV high voltage electron microscope at 673 K to 5.4 dpa (displacements per atom) to study the effect of electron irradiation on microstructure. In situ observation shows the voids formed by electron-beam irradiation coalescence which grew to larger sizes with irradiation dose. Values of void size, void number density and void swelling in HAZ were larger than those of the matrix, and these increased and saturated gradually with irradiation dose. Non-equilibrium segregation phenomenon involving Cr depletion and Ni enrichment at grain boundaries were also observed in both the HAZ and matrix of welded SUS304 steel.

This paper concerns the liquid phase sintering (LPS) process for the fabrication of SiC based ceramic materials and their characterization. The submicron SiC powder was also utilized for the improvement of LPS-SiC materials. A thermal exposure test was carried out to examine the high temperature stability of LPS-SiC materials. A mixture of Al 2 O 3 and Y 2 O 3 particles was used as an additive in the LPS process. LPS-SiC materials were fabricated by various sintering parameters such as sintering temperature, additive composition ratio (Al 2 O 3 /Y 2 O 3 ) and additive amount (Al 2 O 3 + Y 2 O 3 ). The strength of LPS-SiC materials was examined at room temperature using a three-point bending test. LPS-SiC materials fabricated at 1820 °C had a density of about 3.1 g/cm 3 and a flexural strength of about 780 MPa. However, the strength of LPS-SiC materials substantially decreased after the thermal exposure at 1400 °C for 10 h in the Ar atmosphere, due to the dramatic increase of weight loss by severe erosion.

The high Mn-Cr austenitic steel for structure material of nuclear and/or fusion reactors from the point of view of the reduced radio-activation has been irradiated by using three irradiation modes of electron-beam irradiation, electron-beam irradiation after He-injection and electron/He+-ion dual-beam irradiation in 1250kV high voltage electron microscope (HVEM) connected with an ion accelerators to study the effect of He-injection on irradiation damage. Irradiation-induced segregation analyses were carried out by an energy dispersive X-ray analyzer (EDX) in a 200kV FE-TEM with beam diameter of about 0.5nm. Void formation was not observed in each irradiation condition. Grain boundary migration was observed in the case of electron/He+-ion dual-beam irradiation. Irradiation-induced segregations of Cr and Mn at grain boundary were observed in each irradiation condition. The amounts of Cr and Mn segregation decreased in the cases of electron-beam irradiation after He-injection compared with other irradiation conditions.

Four kinds of raw C/C composites with a density between 1.25~1.66g/㎤ were used in order to investigate the effect of the initial porosity of C/C composites on mechanical properties of liquid silicon infiltrated C/SiC composites. The microstructure observation, image analysis and flexural strength test of the composites were performed. The density and microstructural changes with the variation of the initial porosity was discussed in the terms of the infiltration behavior of liquid silicon and the reaction between liquid silicon and matrix carbon.

The heat affected zone (HAZ) of welded SUS304 steel has been irradiated using three irradiation modes of electron single irradiation, electron irradiation after He-injection and electron /He ion dual-beam irradiation by 1250 kV high voltage electron microscope (HVEM) connected with an ion accelerator. Void size in the specimen with pre-injected helium increased considerably and the void size distribution was a bi-modal. Void swelling is the highest in the case of electron irradiation after He-injection. The segregation of solutes of Ni and Cr near grain boundary was suppressed in the cases of electron/He þ -ion dual-beam and electron irradiation after He-injection comparing with electron single irradiation.

The interaction between dislocations and nitride precipitates during high-temperature creep deformation of high manganese austenitic steels has been investigated by transmission electron microscopy. Most of the dislocations activated by applied stress were dissociated into Shockley partials. The fine TiN precipitates are pinning and/or incorporating the bow-type moving dislocations and they turned out to be more effective than the coarser TaN in disturbing the dislocation movement.

The heat affected zone (HAZ) of a welded SUS304 steel has been irradiated in an 1250 kV high voltage electron microscope at 673 K and up to 5.4 dpa (displacements per atom) to study the effect of electron irradiation on microstructure. The dislocation loop density of initial irradiation state increased with electron irradiation dose. Void size, void number density and void swelling increased and then saturated gradually with irradiation dose. The depletion of Cr and the enrichment of Ni at the grain boundary were also recognized by EDS analysis in the HAZ of welded SUS304 steel.

Using the DV-Xa cluster method, two alloying parameters were calculated in fcc Co. One was the bond order (Bo) which is a measure of the covalent bond strength between atoms and the other was the d-orbital energy level (Md) of alloying transition elements. These two alloying parameters were found to change monotonically with the atomic number of alloying 3d transition metals, M. The changes in the Bo with alloying elements could be understood in terms of the difference electron density maps. Also, the Co-M binary phase diagrams could be classified well using Bo-Md map. In addition, local spin moments at the alloying 3d transition metals were obtained. These results will provide us some guide for the design of cobalt-based alloys.