In order to develop the nondestructive outgoing inspection method that determines the surface conditions in the induction-hardened carbon steel, X-ray diffraction method was applied both to estimate the surface hardness and to predict the hardened zone depth using micro X-ray beam adjusted by the pinhole collimator. In this study, S48C hardened specimen cut from the root circle of drive gear was used. The Vickers hardness distribution and 2/5-value breadth of X-ray diffraction patterns of 100, 200 and 211 planes for ferrite and martensite phases were measured from the hardened zone, and then a correlation between hardness and 2/5-vale breadth was examined. As a result, the hardness of the induction-hardened zone was proportional to the 2/5-value breadth. From the obtained relationship, the surface hardness could be nondestructively estimated by measuring the 2/5-value breadth from the induction hardened carbon steel. Furthermore, by making a master curve for the subsurface hardness distribution of the mass produced parts in the optimum condition, the residual hardened zone depth could be also predicted from the measured 2/5-value breadth. The predicted hardened zone depths in the induction hardened drive gear agreed very well with the results measured by removing the surface layer.
Tensile tests were carried out for electro-deposited copper foils. The thickness of the foils was 8μm and 20μm. The effect of the thickness on the deformation behavior and the tensile strength was investigated. The tensile strength of the thicker foil was slightly lower than that of the thinner foil. On the other hand, the elongation of the thicker foil is larger. In-situ X-ray stress measurement was conducted to estimate the deformation damage of the foils under tensile loading. In the elastic region, the stress measured by the X-ray was identical to the applied stress. However, when the plastic deformation occurred, the discrepancy between them became large due to the intergranular strain. The discrepancy of the thicker foil was larger than the thinner one. Then the fatigue tests were carried out. The fatigue strength of the thinner foils was higher. The thickness effect for the fatigue strength was larger than that for the tensile strength. The full width of half maximum, FWHM, was a function of both the applied stress and the number of stress cycles. Change of the value of FWHM with stress cycles corresponded to that of the maximum applied strain. The fatigue damage could be evaluated on the basis of the value of FWHM.
Thermal barrier coatings (TBCs) were made on the round bar substrates of which radii were 5, 10 and 15mm. In addition to the round bar substrates, the TBC was made on a plate substrate. First, NiCoCrAlY was pressureless plasma-sprayed as bond coating, and then zirconia with 8 mol% yittria was air plasma-sprayed as top coating. The TBC specimens were exposed in air atmosphere at 1373K for 0h, 200h or 500h. The radial strain was first measured with the strain scanning method using high energy synchrotron X-rays. The hoop and axial stresses of the round bar specimens were measured using laboratory X-rays with successive removal of the surface by polishing. Using these measured stresses and strain, the distributions of the 3-dimentional components of the residual stress in the top coating were determined. The spalling stress became a maximum at about 50μm apart from the interface. This position corresponded to the location of initiation of the spalling cracks. The maximum of the measured spalling stress increased with the decrese in the radius of curvature. The difference of the measured distribution of the residual stress from the calculated distribution of the thermal residual stress was explained on the basis of the characteristic of the top coatings, such as the stress relaxation due to sliding between lamelli, a binding effect by the interface roughness and the spalling stress induced by the interface roughness.
Laser pulses with about 0.2J energy and 8ns duration from a frequency-doubled Nd : YAG laser were focused to 1mm and irradiated to the water-immersed sample of high tensile strength steel (JIS SHY685) without coating. Various laser scanning patterns i.e., single spot, line and area, and irradiating pulse density were examined to understand the generation process of a compressive field in area scanning. The detailed distributions of the surface residual stress on the specimens were measured using synchrotron radiation. A tensile residual stress was observed in the center region of the single spot, whereas a compressive field appeared around the spot. In the line scanning, a tensile component was observed in the final spot of the line, however it decreased and changed into compression by the increase in the number of the irradiating pulses. It can be concluded from these results that the compressive residual stresses in the line and area scanning were generated by off-center overlapping of successive laser pulses.
A strain scanning method was applied to the stress measurement of austenitic stainless steel (SUS304L). The sizes of its gauge volume were a width of 2 mm and a height of 0.2mm, and the grain size of the specimen was 37 micrometers. Enough accuracy of the measured stress was not obtained due to the coarse grain of the specimen. To improve the coarse grain problem, three methods of oscillation were examined such as in-plane rotation, out-of-plane tilt and translation. The translation method can increase the number of the grains by changing the amplitude. For the translation method, the accurate measurement is possible if it is 10000 numbers or more of grains. However, the numbers of the grains by the other oscillations were not enough. For the translation method, a strict parallel between the specimen surface and the translation plane was necessary. It succeeded in adjusting the strict parallel. The residual stress distribution of the shot-peened austenitic stainless steel was measured by our method.
The strain scanning method was widely used for the measurement of the stress distribution beneath the specimen surface. For the strain scanning method, the diffracted beams are defined by slits so that only a small illuminated volume can diffract into the detector. When making measurements near surfaces some of the gauge volume may lie outside of the sample, in which case the center of the gauge is not coincident with the center of the diffracting volume and the measured diffraction angle changes even in the stress free materials. In the present study, the stress distribution of the shot peened material was measured by the strain scanning method using neutron and synchrotron radiation. For the neutron method, two kinds of optical system were adopted. At first, the vertical slit system was used for the transmission measurement. Then the horizontal slit system was adopted to avoid the surface effect. When the obtained data was corrected by the stress on the surface measured by the conventional sin2ψ method, the stress distribution measured by the neutron method agreed very well with that obtained by the synchrotron method and the surface removal method using conventional X-ray.
Recently, SiC ceramic was synthesized from bamboo-charcoal and melted Si in an Ar atmosphere. The SiC formed around the inside pore of the bamboo-charcoal as a tubular ceramic. As a result, yield of the SiC ceramic reached about 30%. The product heated for various time (0.1h-5h) was analyzed by scanning- and transmission- electron microscopes with energy-dispersive spectroscopy. For 0.1 hour heating time, the product was composed of SiO2 as an amorphous state or SiC-SiO2 with complex structure. The SiO2 was formed easily because of residual oxygen in a furnace. The SiO2 was existed as a liquid phase at high temperature and accordingly the product shape was like a surface structure of bamboo-charcoal. Increasing the heating time, the SiO2 was reacted with C under Ar atmosphere and became SiC, and increased the SiC thickness < about 14μm. The SiC ceramic possessed 3C structure, and the tendency to decrease by heating was seen as for the stacking disorders in interguranular.
The nanotubular products were synthesized by hydrothermal treatments of anatase-type TiO2 in NaOH aqueous solution. In order to clarify the consolidation of nanotube, the effect of several washing treatments with deionized water, HCl solution, or dehydrated ethanol, on the structure and the composition of nanotubes was investigated in this study. Especially, the characterization of microstructure of these nanotubular products was examined by X-ray diffraction (XRD), transmission electron microscopy (TEM), and X-ray absorption fine structure (XAFS). As a result, it was found that nanotubes were formed during the hydrothermal treatments, not during the washing treatments. In addition, it was clearified that the nanotubes were composed of layered Na-Ti-O, and H-Ti-O nanotubes were obtained by ion-exchange of Na+ for H+ in Na-Ti-O nanotubes by washing with deionized water or anhydrous ethanol and successively with HCl solution.
The hardening mechanism of refractory patching materials with a phosphate binder was investigated by means of 31P static and magic angle spinning (MAS) nuclear magnetic resonance (NMR) spectroscopy. Ten refractory patching materials were made of refractory powders of SiO2 and fused alumina and five mixed solutions of phosphoric acid and aluminum biphosphate as phosphate binders. 31P static and MAS NMR spectra were measured of five phosphate binders and twenty soft and hard refractory patching materials, respectively, to reveal the local structure around P atoms. The 31P static and MAS NMR spectra revealed that PO4 tetrahedra in the phosphate binders have no P-O-P linkage between PO4 tetrahedra and that as the patching materials become hard, the ratio of PO4 tetrahedra with bridging oxygens increases, respectively. This result suggests that the hardening of the patching materials is caused by the condensation of the phosphate binder. But the ratio of PO4 tetrahedra with bridging oxygens was not enough to form the network by P-O-P linkage between PO4 tetrahedra. On the basis of these results, the hardening mechanism of refractory patching materials with a phosphate binder is proposed.
In order to prepare rare earth oxide containing glasses that have high melting temperature, a CO2 laser was employed. This method was shown to be easier than the process of using an electric furnace which is normally used in preparing glass at a high temperature. Glass forming regions of SiO2-Ln2Oy and 0.4CaO · 0.6SiO2-Ln2Oy system (Ln = Ce, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu ) were investigated and the thermal stability of obtained glasses were evaluated by crystallization peak temperature measured by differential thermal analysis. The glass forming regions of SiO2-Ln2Oy systems were narrower than that of 0.4CaO · 0.6SiO2-Ln2Oy systems. The SiO2-Tb2O3.5 system showed the widest glass forming region while the SiO2-CeO2 system showed the narrowest among SiO2-Ln2Oy systems.
Fracture energy is one of important parameters in estimating the resistance of crack propagation for refractories. However, the effect of the dimension of a test specimen on the fracture energy has not been sufficiently studied. In the present study, effective fracture energy γeff of chamotte refractory was evaluated using WOF (work of fracture) technique, in order to investigate the relationship between the fracture energy and specimen dimension. The γeff was significantly dependent on specimen dimension and notch length. Larger specimen dimension and shorter relative notch length made the γeff increased. For instance, the γeff of the large specimen was approximately three times as large as that of the small specimen. To evaluate accurate γeff for the refractory, a specimen with ligament longer than a given length was required. The ligament length was discussed in relation to the size of a frontal process zone.
We fabricated alumina/molybdenum (Mo) nanocomposites. To prepare very fine Mo powder, molybdenum oxide (MoO3) powder was dissolved in 28% ammonia solution. Alumina powder was then mixed with the neutralized MoO3 solution in ethanol using a ball mill. After drying, a pulse electric current sintering method was used for sintering the mixed powder at 30MPa for 5min in vacuum in the temperatures ranging from 1250°C to 1550°C. Three-point bending and fracture toughness (SEVNB) tests were carried out on the specimens of 2 × 2 × 10mm in size. The results showed that the maximum values of the fracture strength and the fracture toughness were 860MPa and 5.22MPa · m1/2 for the specimens sintered at 1450°C, respectively. The specimens with the highest fracture toughness were then annealed at 800°C, 900°C, and 1000°C from 0 to 10min. The fracture toughness of the specimen annealed at 800°C for 10min increased from 5.22 to 5.67MPa · m1/2. The strengthening and toughening mechanisms of the alumina-Mo nanocomposites were discussed with emphasis on dislocation activities.
Typical calcium silicate powder, wollastonite, was mechano-chemically activated in air for 24h with a vibration ball-mill. The cakes of the vibration ball-milled wollastonite added with a fair amount of water and Pressurized Fluidized Bed Combustion (PFBC) ash were carbonated at 80°C in 0.33MPa CO2 for 3h. The removal efficiencies of phosphorous for the carbonated specimens were investigated by immersing them in Na2PO4 aqueous solution containing 5ppm phosphorous. After immersing the specimens for prescribed duration in the test solution, the remaining amount of phosphorous in a supernatant liquid was measured by an inductively coupled plasma spectroscopy or a molybdenum blue method. Ca ion concentrations dissolved from specimens were measured with a selective electrode instruction. The addition of PFBC ash containing calcium sulfate increased a pore volume of the consolidated wollastonite by carbonation and the Ca ion released into water. As a result, the removed efficiencies of phosphorous for the specimens markedly improved compared with those without PFBC ash. The removed rate of phosphorous showed large temperature dependence, and crystallization process are thought to be the rate determining one of the phosphorous elimination.
Equal Channel Angular Pressing (ECAP) has potentiality for producing ultrafine-grained polycrystalline metals in bulk with very high yield stress and excellent workability, under an optimized processing condition. In this study, molecular dynamics (MD) simulations were performed in order to reveal the dependence of metallographic structure evolution on the processing route, and also to clarify the grain refinement mechanism in α-iron by ECAP with a 90° die. We used Lees-Edwards periodic boundary condition to impose a severe plastic deformation which is ideally equivalent to the simple shear deformation produced at the intersecting plane of two channels. The transition of the internal structure during 4 passes were investigated for the feasible four kinds of processing route under quasi 3-dimensional condition. It is shown that the twinning deformation is dominant for the analyzed material, and the texture evolution is notably affected by the relationship between applied simple shear direction and the characteristic crystal orientation which can easily cause twinning deformation. The simplest processing route with no rotation of billet between passes, which is called Route A in general, is the most efficient route in the presently analyzed cases. This is because the twinning deformation along the simple shear direction intersects with the twin boundaries which are developed by stress component conjugate to the simple shear.
We investigate nonlinear energy localization called intrinsic localized modes (ILMs) in two dimensional lattice systems for its application to the dynamics of materials in atomic scale. At first, we calculate quasi-one dimensional ILMs in two dimensional lattice systems with nearest and second-nearest ideal interaction potential. We find that ILM can exist in this system and that the structure of ILM can be affected by the structure of the system. Then we investigate energy localization in graphene sheet by molecular dynamic simulation. Energy localization with finite lifetime which is similar to ILM can appear in the system. These results indicate that ILMs can be excited in materials.
Degassed processing (DG) is used for decreasing cast defects such as porosities or micro shrinkage. So it is very excellent method for improvement of fatigue property on casting aluminum alloy. In this study, for the aim of more fatigue property improvement of the casting aluminum alloy AC4CH, the laser peening treatment was applied to DG treated cast aluminum alloy, and rotating bending fatigue tests were carried out. As the results of fatigue tests, the fatigue life property of the laser peened DG material was more improved. To investigate the cause of the fatigue life improvement, fracture surface of all specimens were observed with SEM. And surface cracks were observed using replication technique. As a results, although the ratio of fatigue crack initiation life to total fatigue life was decreased by laser peening treatment, the fatigue crack growth rate was decelerated by compressive residual stress caused by laser peening treatment. In addition, residual stress at the surface of laser peened specimen was estimated from the result of fatigue crack propagation behavior. And then the estimated residual stress value corresponded with the value of X-ray diffraction method.