This article overviews a unified approach for deriving rate equations for various diffusion-controlled deformation and fracture processes. The basic concept behind the present approach is that the change in the overall free energy of a deforming materials is identified as the total driving force of diffusion. Conventional basic equations on the excess chemical potential of an atom derived by Herring are not directly used in the present analysis. As possible driving forces of diffusion, the changes in surface, grain-boundary and elastic strain energies of the material and the change in the potential energy of an external load are considered. Approximate and exact solutions are derived. The approximate solutions enable us to quickly grasp the physical meanning of the processes and the exact solutions enable us to incorporate effects of various driving forces of diffusion into rate equations in a physically clear manner. Several different diffusion-controlled processes are treated as examples: the Nabarro-Herring creep and Coble creep, grain-boundary sliding, climb of an edge dislocation, growth of a grain-boundary void, shape change of a nearly spherical particle and stress relaxation in a dispersion-hardened material.
Feow structures of the two-phase subsonic jet impinging on a flat plate normal to flow are described focusing upon the particle size. First, the flow properties for both gas- and particle-phases are numerically solved in the region from the reservoir to the nozzle exit, and then flow fields in the free jet, impingement and wall jet regions are solved as a perturbation from the nozzle exit condition. Some of significant characteristics are pointed out for results of the numerical experiments concerning mist flows composed of air and water-droplets. The flow fields for both gas- and particle-phases strongly dependent upon the particle size. When water-droplets mixing in the mist are very small, particles after the impingement of the mixture jet on the surface travel very closely to the surface along the radial direction. With increasing particle size, rebounding particles scatter not only near the surface, but also over the almost whole computational domain. Again, the distribution of vorticity is concentrated on the boundary of mixture flow and varies according to the particle size. The flow field is not necessarily steady, but changeable in a nearly periodic manner.
For the better understanding of the phenomena in the cold crucible, advanced models for electromagnetic field have been developed for both vertical and horizontal cross sections of the crucible. In the former model, the axi-symmetric steet geometry was assumed and the influence of the number of slits was taken into account by the use of a parameter representing the magnitude of the electromagnetic interaction. In the latter one, the conservation problem of the current density in a finite cell was successfully solved through the introduction of Newton's method for the simultaneous convergence of both scalar and vector potentials. The validity of the models was confirmed through experimental measurements of the magnetic flux density, the coil voltage, and the elevation height of the Al-Cu alloy melts. Regardless of the number of slits and the shape of the crucible, the induced current on the intenal and the external sheets of the crucible flows on the horizontal path. An increase in the number of slits resulted in the increase of the magnetic flux density. This is mainly explained by the reason that the partition ratio of the induced current into the segmented part of the crucible increases with the number of slits. Since the melt is expected to contact with the internal wall near the slit bottom in the case of the straight type crucible, the solidification is preferable to be completed just above the slit bottom for the improvement of the ingot surface during continuous casting.
Kinetic experiments have been made on C oxidation between FetO containing slag and molten iron of high C concentration ([%C])≅4.4) at 1300°C under mechanical stirring conditions. Effects of Si and P in the metal and P in the slag on the C oxidation reaction rate have been examined, as well as effect of mechanical stirring on the reaction rate. The C oxidation rate is considerably reduced by slight increase in P concentration in the slag. It is also found the P in the metal has no significant effect on the C oxidation rate. The C oxidation rate decreases with increasing Si concentration in the metal. A mathematical model is proposed to explain the simultaneous reactions in this slag-metal system.
The geometrical features of 12 kinds of polyhedrons were investigated, and the results were applied to the relationship between the grain shape and the size. Taking account of grain size and shape distribution, an expression for grain growth was proposed. The expression was used to investigate the effect of the grain size distribution on the growth rate. It was found that the growth rate increased with increasing variation coefficient and with decreasing kurtosis. It was also found that growth exponent n was 2.2 during the steady growth.
The erosion of the metal-ceramic particles dispersion composite materials was experimented for the purpose of improving the erosion resistance of the elbow for the transportation line of solid particles. The composite flat plates were made by casting method adding the alumina particles of 3 mm diameter into each matrix. The effects of the impingement particle and the impingement angle on the erosion of the composite were investigated. It was made clear that the erosion ratio of the composite was decreased to a half of the average value of the matrix only. Then, the improvement of the erosion resistance of the trial composite elbow was confirmed.
The effects of V on the disbonding characteristics of the 2 1/4Cr-1Mo steels overlayed by austenitic stainless steel were metallurgically studied. The addition of V to the 2 1/4Cr-1Mo steels significantly increases the resistance to disbonding. The scanning transmission electron microscope and energy-dispersive X-ray spectrometer observation showed that the V-modified and ordinary 2 1/4Cr-1Mo steels had different fine precipitates in terms of morphology, distribution and composition. The analyses of hydrogen diffusion and hydrogen evolution indicate that the fine precipitates in the V-modified steels trap hydrogen to increase the solubility of hydrogen and also decrease the diffusion of hydrogen. A theoretical calculation of hydrogen distribution during cooling from the atmosphere of elevated temperature and high pressure hydrogen indicates that both diffusion and solubility of hydrogen in the base metal affect the concentration of hydrogen at the interface between the base metal and the stainless steel overlay. It is concluded that the fine precipitates in the V-modified 2 1/4Cr-1Mo steel increase the resistance to disbonding by reducing the concentration of hydrogen at the interface during cooling.