Transient thermal analysis of solidification in a centrifugal casting for composite materials containing particle segreg
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I.
INTRODUCTION
DURING centrifugal casting processing of metal matrix composites,it-41 segregation of particles occurs due to centrifugal forces, either to the outer or to the inner part of the casting, depending on the relative densities of particles and the matrix. Various processing parameters, such as pouring temperature, solidification time, pouring pattern, and thermal properties of the particles and matrix, will significantly influence the spatial arrangement of dispersed particles and the solidification microstructure which evolve during the centrifugal casting of composites. Determination of temperature distribution during the centrifugal casting process and further determination of the solidification time of centrifugal castings by experimental techniques are very difficult, as the mold rotates at a very high speed during solidification. Because of this, accurate data on solidification time of centrifugal casting are not available. In particular, no data are available on the solidification time during centrifugal casting of metal matrix composites. Therefore, it is necessary to estimate the solidification time and the influence of other processing parameters on the solidification time in the case of centrifugal casting of metal matrix composites through indirect means. Analytical methods involving heat- and mass-transfer analysis can be useful under such circumstances. Estimation of the solidification time and temperature distribution during solidification through heat- and mass-transfer analysis under realistic conditions in an alloy containing dispersed particles or fiber is a complex problem. The situation is further complicated in the case of centrifugal castings as the moving particles disturb the temperature equilibrium.
Also, the segregation of particles either at the inner periphery or at the outer periphery significantly influences the heat-transfer coefficient at the metal-mold interface and the thermophysical properties of the solidifying material. The existing heat-transfer models used by various investigators[5.6.~] predict temperature distribution in the mold and the molten metal for monolithic alloys for very simple cases. In recent years, one-dimensional analysis of heat flow in the presence of one or a greater number of particles has been completed.t~l However, such analyses are not applicable to a solidifying slurry when it is centrifuged. In the process of centrifugal casting, the reported modelingVg~ is limited for phase transformation considering the latent heat of solidification. The temperature distribution of the alloy can have an effect on a particle's moving velocity. However, it was assumed as negligible in the reported modeling. The present study describes results of a heat-transfer analysis of centrifugal casting of metal matrix composites by one-dimensional analysis considering the thermal mechanical properties due to particles moving as a function of temperature. These theoretical predictions were compared with Lajoye and Suery's results.~91 As a first step, the positions
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