The Thinking on Multiphase Materials

Abstract

The main problems for multiphase materials are the even mixing and the bonding or reacting among two or more phases, as well as the states of their grain boundaries. The mixing of two phases is usually effective by using liquid medium. The technology of second phase coating for the original particles or so call nucleo-shell structure is a well approach for the even mixing. For ceramic matrix multiphase materials low sintering temperature is the effective way to avoid the occurring of reaction between different phases. The design of grain boundary and its stress is important for their bonding states. The thinking for above problems would be described briefly in this paper. The purpose of multiphase materials design is expected that every phase will be playing its role, combining together and then given out a comprehensive performances. So it is necessary to consider the following problems. 1. Even mixing Even mixing between each other material is important for multiphase materials. It’s the better when the processing is carrying on in the liquid state for the even mixing of two phase materials. Using physical or chemical method could be formed the fine solid particles with even dispersion of two or more phases materials. Usually it could be obtained nano-scale particles. The application of nano-technology is necessary. The nano-scale mixing of two phases materials would be greatly increased the contacting surface of each other particles without agglomeration. Of course, if one phase of material is fine solid particle which disperses in another phase of material solution, the even mixing of two phases is obtained similarly. Making a coating to other phase particle is a very good approach for the two phases even mixing. Coating process is attracting more and more attention in the preparation of composite materials mainly due to its predominance in the improvement of the uniformity for different phases [1]. The thickness of coating material determines the amount proportion of two phases which is able to be control. Two examples of so-called “nucleo-shell structure” will be introduced in the following parts. Cermet composites have been widely studied due to their potential for achieving higher toughness and reasonable strength compared with ceramic matrix. But except for numbered systems, such as Co/WC and Ni/TiN, few systems have reached the people’s expectation mainly for the poor wettability between metal and ceramic. Al/Al2O3 cermet is a low density and high strength material, and it has many potential and actual applications in military, industrial and consumer regions. To improve the dispersive uniformity of the two phases, coating aluminum with alumina may be a good candidate since such coatings not only stabilize aluminum dispersions but also make it possible to control inter-particle and particle-matrix interactions [2]. Figure1a-c shows the images