To develop a novel recycling process of WC-Co cermet scraps, hydrothermal oxidation treatment of various WC-Co cutting tools was investigated. Four kinds of WC-Co chips were used as samples: the sample A contained 13% of Co and was fine-grained, the sample B contained a small amount of TaC (ca. 1.5%) in addition to 6% Co, and the samples C and D were coated chips on normal WC-Co substrates. The sample was enclosed in a high pressure container lined with polyfluorocarbon resin with an appropriate concentration of nitric acid in the presence and absence of fluoric acid. As a result, pure WO3 powder was selectively recovered from all samples by the hydrothermal oxidation treatment in 7mol/dm3 HNO3 and 2mol/dm3 HF mixed aqueous solution. Other elements such as Co, Ta, etc. were dissolved into the solvent. In conclusion, the present hydrothermal oxidation method was found to be one of the superior methods to recover W and Co resources from WC-Co cermet scraps.
Single phase m-ZrO2 ceramics (∼13mmφ and 3-5mmt) have been fabricated using a piston-cylinder type high-pressure apparatus under 1GPa at 1023-1173K, in which a newly developed high-pressure cell has been utilized to introduce pseudo-isostatic pressure. Starting material, meta-stable m-ZrO2 powder prepared via a sol-gel method, was characterized by X-ray diffraction (XRD), differential thermal analysis (DTA), and transmission electron microscopy (TEM). Dense ceramics sintered at 1123K, free from macro-cracks, showed a high relative density of ∼ 99.5% and homogeneous microstructures consisting of fine grains (∼1μm). In-situ XRD analysis under high pressures and temperatures revealed that m- to t-ZrO2 transition took place around 1123K under 1GPa. Mechanical properties of m-ZrO2 ceramics have been evaluated ; the maximum values of bending strength (σb = 520MPa), Vickers hardness (Hv = 9.8GPa), and fracture toughness (KIC = 3.9MPa·m1/2) were achieved at the samples fabricated at 1123K.
Crack propagation test is carried out in high temperature fatigue of a Nickel-based directionally solidified (DS) superalloy, where the DS, load, and crack propagation axes are set to be perpendicular to each other. The magnitude of J-integral are estimated by the finite-element-method using 2-dimentional models; (i) with the actual crack shape and grain configuration, (ii) with the straight crack in homogeneous body, and (iii) with the actual crack shape in homogeneous body. The driving force (J-integral) of crack propagation is affected by two factors, the local crack propagation direction and anisotropy due to the grains. The former causes the sporadic drop of J-integral at the point where the crack direction is largely apart from the direction normal to the load axis. The latter causes the stepwise change in a (crack length) - J relationship which directly relates to the change of crack propagation rate in transgranular cracks. Then, the relationship between the J-integral which takes into accounts the factors and the crack propagation rate in transgranular crack shows a good correlation to a certain extent. The J-integral at the grain boundary cracking largely fluctuated and shows higher average magnitude than that in the other part. da/dN-J relation reveals that the intergranular crack has weaker resistance against propagation than that in the transgranular one, though it shows eminent fluctuation.
Using a hot isostatic pressing (HIP) technique, diamond/SiC composites were synthesized from diamond and Si powders. At an HIP condition of 1450°C and 100MPa, a pressure much lower than that of the diamond stability field, diamond powders react with molten Si to form well-sintered diamond/SiC composites. Cubes of the composites with 15mm edge length were thereby fabricated, and an application to the second stage anvils in a Kawai-type high-pressure apparatus was attempted. The anvils were proved to be hard enough for the generation of pressures up to 30GPa. For high-pressure and high-temperature in-situ X-ray experiments using synchrotron radiation, a hybrid anvil system using 4 cubes of the composites and 4 of conventional WC was introduced and heating experiments up to 1600°C at 20GPa became possible. Because the diamond/SiC composites are transparent to X rays, the present system is applicable not only to diffraction studies but also to radiographic studies that need a larger window for an X-ray image.
For numerical design of safety compartments in a cabin of aircraft to maintain a survivable environment for passengers in a crash, very-high-strain-rate mechanical-properties of many kinds of aerospace materials are indispensable. On the basis of the Unsteady Wave Sensing System (UWSS), which is composed of a plate impact experiment using three in-material gauges and nanosecond Lagrangian analyses, various variables are determined at the sensing part of the central gauge. Three stress-time histories are measured by three PVDFgauges, respectively, and the time histories of the phase velocity associated with the stress : Uσ, particle velocity : v, the phase velocity associated with the particle velocity : Uv, and strain : ε induced by impact at velocities ca. 600m/s are calculated by using those three stress-time curves and the conservation relations of mass and momentum. Then, the stress-strain curves at very high strain-rate of the order 106 to 107s−1 are derived under conditions of uniaxial strain. On the other hand, stress-stain curves at medium strain rate (ca. 102s−1) and at low strain rate (ca. 10−4s−1) under conditions of uniaxial stress were already determined by a drop-weight testing system and Instron testing machine, respectively. It is clearly shown that the stress-strain curves for PMMA and polycarbonate (PC) are both very sensitive to strain rate in the very wide range of strain-rate of 10−4s−1 to 107s−1 under conditions of uniaxial strain. As a result, power law relations between stress and strain-rate were observed with these glassy polymers under uniaxial strain conditions in the very wide strain-rate range.
Solid phase epitaxy (SPE) of Si is one of the most fundamental processes in semiconductor fabrication techniques. Many experimental studies have been carried out for understanding the growth mechanism. However microscopic mechanism is not well understood. In this study, we investigated the effect of arsenic atoms on the rate of Si SPE by using molecular dynamics simulation. In the case of non-doped Si, an activation energy of SPE is found to be 2.1±0.5eV, which shows good agreement with the experimental result (2.7eV). It is also found that the energy barrier of crystallization in a/c interface amounts to be about 0.6eV, which corresponds to defect migration process. It indicates other processes such as defect formation also control the SPE process. The SPE rate increases by 2 times for 3 at% As doping and 100 times for 5 at% As doping and an activation energy remains to be constant. The increase in SPE rate would be enhanced by defect formation process in amorphous silicon, which reflects the increase in self-diffusion of silicon atoms caused by active As atoms.
MEMS micromirror is used as optical switching or scanning devices, etc. Since the device is made from single crystalline silicon, the fracture stress involves large scattering. Therefore, reliability-based design procedure is indispensable. We propose a method to detect the design stress of both static and fatigue strengths. As for static strength, a method to determine design stress by using Bayesian inference is proposed, where the design stress is determined by combining a few number of strength data of actual product and prior distribution based on sufficient experimental data. The proposed method is verified by simulated data through the comparison with conventional maximum likelihood method. It is found that the proposed method is especially effective when there is not sufficient strength data. As for the design stress for fatigue strength, a method to evaluate fatigue life in general working environment by extrapolating the experimental data of accelerated fatigue life tests is proposed. As a result, the fatigue design chart based on 99% prediction interval is shown.
To investigate the extra long life fatigue properties of aluminum die casting materials, fatigue tests were conducted on two type of aluminum die casting materials. One type is Al-Si-Cu die casting alloys ADC10-T5 and the other is Al-Si-Mg die casting alloys AC4C-T6. The main results obtained are as follows, (1) For ADC10-T5, the origin of fatigue crack is casting defect and the fracture surface at around the fatigue crack initiation portions were Mode I fracture surface. (2) For AC4C-T6, the origin of fatigue crack is the base matrix and the fracture surface at around the initiation portion changed from Mode I fracture surface to Mode II fracture surface along with the increase in the number of cycles. At the range of Nf < 105 or about Nf = 105, fracture surface were Mode I fracture surface, about Nf = 106, fracture surface were mixture of Mode I and Mode II fracture surface, and at the range of Nf > 107, fracture surface were Mode II fracture surface. (3) The extra long life fatigue strength (107-109cycles) of AC4C-T6 decreased along with the increase in the number of cycles, while the extra long life fatigue strength (107-109cycles) of ADC10-T5 did not decrease along with the increase of the number of cycles. (4) The casting defect size in non-fracture specimen was much smaller than the allowable defect size predicted by the √area parameter model. It seems to be that the reason why no reduction was recognized in the fatigue strength of the ADC10-T5 in the life range beyond 107cycles.
Fatigue fractures of actual parts mostly start from the sites of stress concentrations at structural discontinuities. In an early study, the fatigue strength of shot blasted ductile cast irons with casting surfaces, the fracture origins of which were at defects, was quantitatively evaluated by using the √area parameter model. However, since some fatigue fractures at the sites of stress concentrations start from surfaces, the quantitative evaluation of the fatigue strength of ductile cast irons whose fatigue origins are at surfaces is also important. In this study, shot blasted ductile cast irons with casting surfaces were employed and plane bending fatigue tests have been conducted for evaluating the fatigue strength of the specimens whose fatigue origins are at surfaces. For quantitatively evaluating the influences of surface roughness and transitional layers at the site around casting surfaces, the defect size √areaR for the surface roughness and the equivalent hardness HVeq considering the transitional layers were applied. Moreover, the relief of residual stress during fatigue tests was detected. The relieved residual stress was regarded to be mechanically equivalent to the mean stress. By using these parameters, the fatigue strength of shot blasted ductile cast irons whose fatigue origins are at surfaces has been successfully evaluated. Furthermore, fatigue tests using an actual part have been performed and the usefulness of the quantitative evaluation method has been verified.
Strain controlled thermo-mechanical fatigue (TMF) and low cycle fatigue (LCF) tests were conducted in a single crystal Ni-based superalloy, CMSX-4, under various test conditions. At first, it was shown ex-perimentally that the superalloy revealed the TMF and LCF lives associated with some unique charac-teristics, which were not always interpreted well, so far as the traditional stress-based and/or strain-based criteria were employed : e.g., Manson-Coffin law and Ostergren method. New micromechanics model is proposed to estimate the TMF and LCF lives taking account of the unique microstructure of superalloys. The proposed method enabled us to estimate some unique characteristics in the TMF and LCF failures of superalloys, although some quantitative hurdles should be overcome further.
The previous work showed that the precipitation of boron nitride at creep cavity surface suppressed the cavity growth and provided a type 304 austenitic stainless steel with a self-healing effect on the creep cavitation. The self-healing effect on the cavitation improved the long time creep rupture strength and ductility remarkably. In order to provide a type 347 austenitic stainless steel with the similar self-healing effect, the composition of the steel was modified with the addition of boron and cerium. An improvement of rupture strength coupled with rupture ductility of the steel was observed with the boron and cerium additions. Mobile sulfur in the steel was removed by formation of Ce2O2S, Ce2S3 and TiS. Auger electron spectroscopic analyses of the chemistry of creep cavity surface, exposed by breaking the crept specimen at liquid nitrogen temperature under impact loading, revealed the segregation of elemental boron on the creep cavity surface. The boron segregation at the creep cavity surface in the absence of sulfur contamination suppressed the cavity growth and improved the creep rupture properties by the self-healing effect of the boron segregation. The self-healing effect of the elemental boron segregation was compared with that of the boron nitride precipitation.
Much research has been carried out on the time-dependent behavior of rocks. It is well known that uni axial compressive strength increases as the strain rate becomes larger. Rock in general mainly contains microscopic cracks. In process to failure, cracks seem to develop parallel to the loading direction from the tip of microscopic cracks. Therefore, it is important to pay attention to the behavior of the circumferential strain when the time-dependency of stress-strain characteristics of rocks is examined. In this study the uni axial compression test are carried out using tuff , and the effect of stress rate on the stress-strain behavior is described.
Although fiber reinforced plastics (FRP) are often used for structural components and functional materials, the vibration reduction for FRP materials is still difficult. The hybrid construction of FRP is well known as more effective for the improvement of this property. In this paper, in order to improve damping characteristics of FRP materials, carbon fabric reinforced shape memory polymer (SMP/CFRP) hybrid laminates are developed. The bending and damping property is investigated by the three-point bending test and mechanical impedance method. The influence of lamination position and contents of SMP in hybrid laminates on mechanical property is discussed. The theoretical formula for bending modulus and bending strength was proposed, and the validity was confirmed by experiment. The results show that the developed hybrid laminates has high bending modulus and excellent damping properties.
In the current manufacture of multi-layer printed wiring boards (PWBs), the method frequently used is to laminate the core with insulating resin as build-up layers. Then, micro-via drilling technology using laser has become the dominant method of drilling smaller blind via holes of build-up layer. Cu direct laser drilling attracts attention to a new method in this field. However, there is no reports dealing with Cu direct laser drilling of PWBs. The purpose of the present report is to research the feature of Cu direct laser drilling and establish the method in order to improve hole quality. Following conclusions were obtained : (1) The technique using the infrared thermography was proposed in order to examine the laser absorptance of the surface copper foil. (2) The method of mixing fillers in the build-up layer was effective to improve hole quality by reducing the difference of the laser processing threshold between the copper foil and the build-up layer. (3) The technique was established to estimate the overusing FEM analysis.