اثر میدان مغناطیسی عرضی بر رشد دانه های هم محور حین انجماد جهت دار

Effect of a transverse magnetic field on the growth

of equiaxed grains during directional solidification

اثر میدان مغناطیسی عرضی بر رشد دانه های هم محور حین انجماد جهت دار

ABSTRACT

The effect of a transverse magnetic field on the growth of equiaxed grains during directional solidification of Al-10wt% Cu alloys was investigated experimentally and numerically. The experimental results show that the magnetic field has a great influence on the size and distribution of equiaxed grains. Indeed, the magnetic field causes refined and coarsen equiaxed grains to distribute on the both sides of the sample, respectively. In-situ synchrotron X-ray imaging shows that a transverse magnetic field induced some force which can act on equiaxed grains and cause the movement of equiaxed grains during directional solidification. Numerical results reveal that the modification of the structure may be attributed to the thermoelectric (TE) magnetic effects produced by the magnetic field. Furthermore, a new method of removing inclusions in molten metal is developed by means of the TE magnetic force.

 

پایداری ساختاری مواد نانوکریستالین – رشد دانه

Stability of structural nanocrystalline materials grain growth

پایداری ساختاری مواد نانوکریستالین – رشد دانه

ABSTRACT

Knowledge of the thermal stability of nanocrystalline materials is important for both tech­  nological and scientific reasons. From a technological point of view, the thermal stabil­ ity  is important for consolidation of nanocrystalline particulates without coarsening the  microstructure.That is, many methods, as described in Chapter 2, for synthesis ofnanocrys­ talline  materials result in particulate products which must be consolidated into bulk form. Since most  consolidation processes involve both heat and pressure, the thermal stability of the nanoscale  microstructure is always at risk. The goal of particulate consolidation is to attain essentially  100% theoretical density and good particulate bonding while preventing or minimizing grain growth  of the nanocrystalline grains. Understanding the scientific nature of stability, grain growth of nanocrystalline  microstructures is a criterion for allowing strategies for minimizing grain growth to be devel­  oped. A basic scientific question with regard to nanocrystalline materials is whether their  behavior involves ''new physics" or is simply the expected grain-size-dependent behavior  extrapolated to nanocrystalline grain sizes. Thermal stability is an important phenomenon to be  addressed in this regard. The thermal stability in a broader sense involves not only the  stability of the grain structure, that is the microstructure, but also the stability of the  structure of the grain boundaries in nanocrystalline materials. A number of investigations on the  thermal stability of nanocrystalline materials have been conducted. Grain growth in  nanocrystalline materials has been reviewed by Suryanarayana (1995), Weissmuller (1996), and  Malow and Koch (1996a,b). In this chapter we will discuss the thermal sta­ bility, grain growth  of nanocrystalline materials with reference to experimental methods for measuring grain growth,  grain-growth theories for conventional grain-size materials which may be applicable, grain growth  (secondary recrystallization) at ambient tempera­ tures in nanocrystalline metals, strategies for  inhibition of grain growth in nanocrystalline materials, and examples of experimental studies of  grain-growth kinetics in nanocrystalline materials.