A new hot hydrostatic extrusion process with a visco-plastic pressure medium instead of liquid was developed. A lump of visco-plastic material is introduced into a container just after charging a pre-heated billet, and extrusion is immediately performed. Therefore, the temperature drop of billet is minimized, and at the same time a steady hot extrusion is realized. With this process, co-extrusions of commercially pure titanium and copper alloy were conducted. And favourable extrusion conditions were determined for sound composite bars. For the co-extrusions of titanium and other materials, a heat-treated or axisymmetrically pre-deformed billet of titanium should be used to obtain an uniform deformation. An intermetallic compound was sometimes observed at the interface between titanium and copper alloy when the extrusion temperature was high, or the annealing temperature after extrusion was high. Under a good process condition, no intermetallic compound was observed and the bonding shear strength was as high as 120-150MN/m2 for the case of a titanium clad copper electrode.
The effects of hydrostatic pressure on deformation and fracture energy at the notch bottom of single V-notch test specimens were investigated experimentally on commercial 7-3 and 4-6 brasses by means of the tension tear and three point bending tests. The specimens were soaked under hydrostatic pressures up to 200MPa for one hour before measuring at atmospheric pressure the transient behaviors of such parameters as the fracture toughness, the unit crack initiation energy (UIE) and the unit crack propagate energy (UPE). The following conclusions were obtained: (1) The initiation of unstable deformation was delayed by applying hydrostatic pressure. (2) The pressure soaking treatment dispersed the dislocations piled up at the grain boundaries. This caused a temporary work-softening, and then the increase of fracture ductility and the decrease of flow stress. (3) A remarkable influence of hydrostatic pressure was observed on the fracture toughness Kc, UIE and UPE in the tear tests. These parameters increased with increasing hydrostatic pressure. This means that both the ductility of fracture and the flow stress increase with increasing hydrostatic pressure. The same results were obtained in the three point bending tests, and they were explained well by the linear fracture mechanics.
Y-PSZ materials containing 2.5 to 5.0mol% Y2O3 prepared by post hot isostatic pressing under oxygen-containing atmosphere (white-Hipping) were found to retain their original strength even after ageing at temperatures higher than 600°C for 1000h. In this paper, the effects of heat-treatment at 1000°C to 1400°C on the bend strength and microstructure of Y-PSZ materials prepared by white-Hipping were reported. The bend strength of 5.0mol% Y-PSZ material after heat-treating at 1100°C for 1000h increased greatly from 720 to 1080MPa. The enhancement of strength was explained by the crack-precipitate interaction (CPI) toughening mechanism. The modulated, tweed or colony structures of fine strip crystals orthogonally crossing each other were observed within the cubic ZrO2 matrix. The 5.0mol% Y-PSZ material showed less decrease in strength at temperatures above 600°C, and higher strength at 1000°C to 1200°C than the 4.0mol% Y-PSZ material.
Supersaturated solid-solution alloys of Al-Ge and Al-GeSi systems up to 10at% solute contents were prepared by means of the high pressure and high temperature solid-solutioning technique. A cylindrical specimen with a size of φ6×6mm was held under a pressure of 5.4GPa at temperatures of 400-510°C for 10 hours, for the solid-solutioning treatment, and then quenched to room temperature. The lattice constants, elastic constants, electrical resistivity, and Vicker's hardness of the specimens thus obtained were measured. The shear moduli of the solid-solutions decreased with increasing solute content, and this feature was discussed in terms of the valence electron per atom ratio and the lattice distortion. By means of the same pressure technique, the solid-solutions of Ti-Al system up to 30at%Al were prepared from the mixed powder of pure titanium and pure aluminum. The shear modulus of the titanium alloy increased with increasing Al-contents.
The high electric field properties of InP have been studied as a function of pressure to 55kbar. The measured threshold field for transferred electron instability showed an initial increase with pressure, and after passing through a maximum at 30-33kbar it decreased gradually. Monte Carlo calculations based on a stronger Γ-L scattering assumption seemed to agree better with the experimental data. The experimental results also indicated that a change from the two- to the three-level operation occurred near 30-33kbar. Photoluminescence (PL) and optical absorption measurements on the heavily doped GaAs have been made as a function of pressure to 60kbar at 77K. With increasing pressure the spectrum shifted towards the higher energy side. The pressure dependence of the emission peak across the direct gap showed a noticeable change in slope at about 30kbar. For pressures above 35kbar the PL intensity suddenly decreased. The pressure dependence of the absorption edge in the heavily doped samples was quite different from that in the undoped or moderately doped samples. The observed behavior can be explained in terms of the effect of high doping on the inversion of the Γ and X conduction bands at high pressure.
Formation of diamond from amorphous carbon was studied under static high pressure (10-18GPa) and high temperature (1120-2000°C) without any planned addition of catalysts. Diamond was formed upon heating amorphous carbon at fixed pressures higher than 10GPa, but was not formed below 8GPa. The formation of diamond occurred via crystallization of amorphous carbon into graphite. The graphitization was not, however, completed prior to the diamond formation. The temperature of diamond formation from amorphous carbon was markedly lower than those from glassy carbon or spectroscopic graphite, being strongly dependent on the temperature for preparing amorphous carbon. The results were interpreted from the two-species model of amorphous carbon.
The X-ray elastic constants of high manganese austenitic cast steel were determined from γ(311) diffraction of CrKβ radiation by the complex oscillation technique using the ψ0 oscillation and specimen oscillation at the same time, and the accuracy of the measurement was examined. The results obtained are summarized as follows. (1) If materials have no residual texture from uniaxial plastic deformation, the value of the X-ray elastic constant KX (KX=-366MPa/deg) of austenitic steel adopted in the standard method of X-ray stress measurement is considered suitable for the high manganese austenitic steel which has been subjected to various plastic working treatments. (2) For the X-ray stress measurement of the coarse grained high manganese austenitic steel subjected to heavy plastic deformation, the error in stress measurements Δσ is 20-50MPa, if the limit of confidence is set at 95%.
A subcritical crack growth due to stress corrosion has been identified as a source of time-dependent fracture of rocks in brittle fields. The stress corrosion cracking was investigated in humid air by using the double-torsion technique for three rocks of different origin, Murata basalt, Oshima granite and Ogino tuff. The subcritical crack growth was found to be strongly dependent on the directions of crack opening and crack propagation. The maximum growth rate was higher by several orders of magnitude than the minimum one for the same rock. The anisotropy in the crack propagation was controlled by microcracks for Oshima granite and by the fabric for other rocks.
Subcritical crack growth has a strong dependence on the directions of crack opening and crack propagation. The maximum growth rate was higher by several orders of magnitude than the minimum one for Oshima granite. From the theoretical consideration on the torsion of two thin orthotropic plates, a way for analyzing the data of the double-torsion technique for anisotropic materials was established. Based on the Christoffel's equation, nine elastic stiffness constants of Oshima granite were determined from the sound velocities, Vp and Vs, propagating in various directions. The results of the anisotropic analysis showed that the observed difference in crack velocity of different directions was not an error due to the isotropic analysis but the intrinsic nature of the granite. A theory based on the microcrack growth model showed that the difference in crack velocity by several orders of magnitude brings in a difference of only several times in dilatancy and that of only several percents in the uniaxial compressive strength.
The precracked specimens of mild steel (JIS: SS41) were tensile tested in liquid zinc kept at various temperatures, T, and the crack propagation behavior and crack propagation mechanism were discussed. The crack propagation velocity da/dt increased with increasing J-integral at every T. Under the same J-integral, da/dt increased with increasing T until T=803K, but da/dt decreased with increasing T beyond T=803K. The crack propagation velocity da/dt was large when the length of intergranular diffusion region was large. The crack propagation mechanism of the steel seemed to be that the zinc vapor, which adsorbed on the crack tip, diffused along the grain boundary to weaken the crack tip area. The J-integral and temperature dependency of da/dt were able to be explained to some degree by a unidimensional intergranular diffusion model.
The surface crack propagation behavior after single overstraining during constant amplitude tests in low-cycle fatigue was studied by using the small holed and through-crack specimens of low carbon steel. The tests were carried out with various kinds of overstrain waveforms and ratios. The results obtained are summarized as follows; (1) During the subsequent crack growth after overstraining the retardation-after-acceleration phenomenon was observed on the surface fatigue crack specimen in the both tension and compressiontension waveforms as well as on the through-crack specimen, and the duration of acceleration for the small holed specimens was longer than that of the through-crack one. The acceleration-after-retardation phenomenon was also observed in the both compression and tension-compression waveforms. (2) The durations during acceleration and retardation increased linearly with increasing overstrain ratio. (3) The stress amplitude after overstraining differed in the tension side and the compression side in such a way that the compression side was larger when the final peak of overstrain was in the tension side, whereas the tension side was larger when in the compression side. But the difference between the stress gradually decreased with increasing cycling, and approached to the saturation value of the constant amplitude tests. In the case of the tension waveform, the decreasing duration was almost the same as the duration during accelation of crack propagation. (4) The value of (ΔJhmax/2σy), evaluated by the J-integral range at the tension side overstraining, was related to the affected retardation and acceleration crack lengths as given by ld/2, la/2=α(ΔJhmax/2σy).
The effects of notch shape and effective case depth on the rotating bending fatigue limit of induction surface hardened S45C steel were investigated. The results are summarized as follows; (1) In the case of fracture from the inner part of test specimens, the fatigue limit became higher with increasing stress concentration factor (α) and effective case depth (ECD). The reason is that the applied stress at the inner part decreases with increasing α, and the fracture origin becomes deep with increasing ECD. (2) In the case of fracture from the surface of test specimens, the fatigue limit decreased with increasing α and ECD. The reason is that the applied stress at the notch root becomes higher with increasing α, and the residual compressive stress at the notch root decreases with increasing ECD. However, when α exceeded a certain value, nonpropagating cracks were recognized and the fatigue limit became almost constant. (3) From the effects of α and ECD on fatigue limit, it is said that the fatigue limit becomes higher with increasing ECD in the case of α<2, while in the case of α>2, the fatigue limit increases with decreasing ECD and the crack initiation strength increases with increasing ECD.
The environmental influences on fatigue strength at high temperatures and creep strength of Hastelloy XR were investigated by using the specimens corroded in helium gas with impurities. The corrosion fatigue strengh at high temperatures in helium gas with impurities was also estimated from the method proposed previously by the authors, and another method proposed in the present study. The latter method assumes that the reduction ratio of fatigue strength at high temperatures in a corrosive environment to that in vacuum is equal to the total of the reduction ratio of fatigue strength due to the aging effect and that due to only the corrosion effect. The estimated corrosion fatigue strength by the latter method was in good agreement with the estimated result by the former method, which can be applied to the estimation of corrosion fatigue strength at high temperature.
The rolling contact fatigue tests were carried out on high manganese austenitic steel to investigate the influence of Cr or Ni addition on the rolling contact fatigue strength by using a Nishihara-type wear testing machine under a lubricated state with a relative slip ratio of -9%. The results obtained are summarized as follows: (1) The rolling contact fatigue limit of high manganese austenitic steel containing Cr or Ni was lower than that of high manganese austenitic steel having the standard chemical composition. (2) The rolling contact fatigue limit of high manganese austenitic steel remarkably increased by the work hardening phenomenon which is generated by repeated contact stress. (3) A crack of high manganese austenitic steel propagated along the boundary of the work hardening zone and the unwork hardening zone in the parallel direction with the contact surface. Its depth was deeper than the region where the stress value calculated according to the maximum shearing stress theory reached the maximum.
A stochastic approach to fatigue damage of carbon fiber composites (CFRP) was proposed. It is based on the constitutive equation for fatigue damage in continuum damage mechanics. By introducing the stochastic process to this equation, a stochastic differential equation of Itô type was derived. The sample path and life distribution of fatigue damage of CFRP were obtained by using the solution of the stochastic differential equation and its probability density, respectively. These theoretical results were compared with the experimental data for a carbon eight-harness-satin/epoxy laminate.
X-ray elastic constants of sintered, hot-pressed and HIP'ed Si3N4 ceramics were determined from various diffraction lines by using CrKα radiation. The measured X-ray elastic constants for (212), (411) and (321) diffraction planes were nearly the same each other and did not depend on the production method. Those for (301) and (210) planes, which were measured in a low diffraction region only for hot-pressed Si3N4, were different from those for the above three planes. Residual stress measurements were tried on the ground surface of hot-pressed Si3N4. Mild grinding by a diamond grinding wheel did not produce large residual stress. However, heavy grinding by a SD140 grinding wheel produced a large compressive residual stress state. A non-liner dψ-sin2ψ relation was observed in the measurement of (212) plane but no systematic deviation from a straight line could be shown in the both cases of (301) and (201) planes. The lack of ψ-splitting behavior means that the deformation was performed homogeneously in microscopic scale during grinding.
The X-ray stress measuring method was applied to investigate a residual stress distribution in the ground surface layer of Si3N4 ceramics and its thermal stability. Residual stress in a heavily ground layer was measured using the diffraction lines (212), (321), (301) and (210) which appear at 131°, 117°, 81° and 54° in 2θ, respectively, by using CrKα radiation. Successive layer removing by lapping and subsequent X-ray stress measurements revealed that compressive residual stress existed throughout the deformed layer which was restricted up to the depth of 20μm even in the case of a heavy grinding condition. There existed a diffraction plane dependence of the measured residual stress values. In order to investigate the thermal stability of residual stress, the specimens were annealed for an hour at each temperature ranged from 770K to 1770K in an argon atmosphere. Annealing below 1000K did not change the initial lattice strain state nor the initial diffraction line width. This means that both macro- and micro-residual stresses are stable at such high temperatures.
Friction and wear properties of epoxy resin (Epikote 828), which was cured with hexahydrophthalic anhydride and filled with layered carbon powders such as natural graphite (NG), manmade graphite (MG), and petroleum coke (PC) in the range of 0-85wt%, were investigated. Particles of the layered carbon powders were dispersed randomly in the composites. The surfaces of the composites were covered with 2-10μm layer of wear powders after testing friction and wear. When the particles oriented in perpendicular to the wear surface appeared, the layer of wear powders took off, producing a new layer. The pV value of the composites filled with NG and MG, which are flat and ellipsoidal in shape respectively, was higher than that of the matrix twice for the 30wt%, 4 times for the 50wt%, and 6 to 8 times for the 85wt%-filled materials. The friction coefficient (μ) of the composites decreased with an increase in content of the carbon powders. The specific wear rate (W) was independent of pV value and decreased with an increase in content of the carbon powders, but that of the materials filled with PC, which has small affinity for the matrix, was larger than that of the matrix. The μ value and, in particular, W value of the composites which were filled with NG treated with coupling agents were lower than those of the composites filled with untreated NG.
In the previous paper, the holding time was found to be an influencing factor for the hydrogen embrittlement of stainless in 3% NaCl solution. In this study, in order to elucidate the relation between the cathodic potential and mechanical properties, the slow strain rate tension tests were carried out under the environment of hydrogen evolution successively after the specimens were held for various time periods in hydrogen evolution potential. The main results obtained are summarized as follows. (1) The embrittlement ratio obtained from the reduction of area decreased continuously with increasing holding time in each setting potential. This tendency became more pronounced at lower setting potential. Consequently, although the contraction of specimen decreased only slightly in every direction, a remarkable embrittlement phenomenon could be found. The same results were also obtained for the time to fracture. (2) The degradation of mechanical properties accompanied with the hydrogen embrittlement was also noticed in the rupture behavior or the observation of fracture surface by S.E.M.. In particular, the results observed by S.E.M. indicated that the transgranular fracture including quasi-cleavage fracture increased in the outside region of specimen and the dimple caused by ductile fracture decreased in the inside region of specimen.
Corrosion of Inconel 600 (I-600) in concentrated NaOH (1-20M) solutions was studied under various temperatures (50-140°C) and potentials. The solution treated (1050°C, 15min) and sensitized (650°C 10hrs) specimens were used. The results are as follows: (1) The polarization curves for the both specimens showed no change in electrochemical behavior in various corrosive environmental conditions at 50°C. However, the both specimens showed three peaks at higher temperatures than 50°C. The solution treated specimen showed a slightly low current density in the primary passive region and a slightly high current density in the secondary anodic peak, compared with those of the sensitized specimen. (2) The films formed on the specimen surface during corrosion tests in 20M NaOH solution at 140°C were made of NiO, Cr2O3 and Fe3O4. (3) The tests of crevice corrosion of I-600 and carbon steel (S15C) showed that general corrosion took place on the solution treated specimen, but the intergranular corrosion under the oxide films took place and it propagated to the crevice in the sensitized specimen.