Preparation of Functionally Gradient Ceramics by Forming a Series of Solid Solutions

普通陶瓷的热膨胀一般低于金属。因此，在由陶瓷和金属组成的复合材料中，由于热膨胀失配而产生应力，然后复合材料有时会破裂。为了避免这种失效，出现了一种新的技术，即使用功能梯度材料（FGM），其特征在于材料从一个表面到另一个表面具有连续变化的性质。这种材料通过形成由陶瓷和金属组成的具有预定组成分布的复合层堆来制备。在这项研究中，功能梯度材料是通过在单一陶瓷体中形成一系列固溶体来制备的。首先，从霞石固溶体（Na_<1-x>M_xAlSiO_4：M=Li和K）制备了热膨胀的功能梯度材料。通过烧结由NaAlSiO_4粉末和{（1-x）NaAlSiO_4 + xMAlSiO_4（M=Li和K）}混合粉末组成的压坯层，它们结合在一起形成梯度固溶体，其成分随离界面距离的变化而连续变化。霞石固溶体具有与金属相同的高热膨胀系数。随着x的增加，Na_ Li_xAlSiO_4的热膨胀系数从<-5>x=0时的1.6 × 10 ~（-1）/oC降低<-5>到x=0.15时的1.2 × 10 ~（-1）/oC<1-x>，而Na_ K_xAlSiO_4的热膨胀系数则增加到<-5>x=0.43时的1.8 × 10 ~（-1）/oC<1-x>。因此，梯度固溶体的热膨胀系数应根据固溶体的组成随位置逐渐变化。其次，FGM的电性能进行了研究。通过<1-x>烧结PZT（A）和PZT（B）相互接触的层状压坯，Zr和Ti相互扩散，在单一陶瓷体中形成一系列PbZr_xTi_ O_3固溶体。具有梯度固溶体的样品的介电常数对温度的依赖性降低。

Thermal expansions of ordinary ceramics are generally lower than those of metals. So, in composite materials composed of ceramic and metal, a stree is developed by the thermal expansion mismatch, and then the composite sometimes breaks up. In order to avoid thisfailure, there is a new technique to use functionally gradient materials (FGM), which is characterized by the material having a continuously varying property from one surface to the other. Such a material is prepared by forming a pile of composite layrs composed of ceramic and metal having the pre-determined compositional distribution. In this study, a FGM was prepared by forming a series of solid solutions in a single ceramic body. First, a FGM with respect to thermal expansion was prepared from nepheline solid solutions (Na_<1-x>M_xAlSiO_4 : M=Li and K). By sintering green-compact layrs composed of NaAlSiO_4 powder and {(1-x)NaAlSiO_4 + xMAlSiO_4 (M=Li and K)} mixed powder, they bonded together to form a gradient solid solution, which compositon continuously varied with the distance from the interface. Nepheline solid solutions had high thermal expansion coefficients equal to those of metals. The thermal expansion coefficient decreased from 1.6x10^<-5>/ﾟC for x=0 to 1.2x10^<-5>/ﾟC for x=0.15 in Na_<1-x>Li_xAlSiO_4, and increased to 1.8x10^<-5>/ﾟC for x=0.43 in Na_<1-x>K_xAlSiO_4 with increasing x. Consequently, the thermal expansion coefficient of the gradient solid solutions should gradually vary with position according to the composition of solid solution. Second, a FGM with respect to electrical properties was investigated. A series of PbZr_xTi_<1-x>O_3 solid solutions was formed in a single ceramic body by sintering layred compacts of PZT (A) and PZT (B) in contact with each other, where Zr and Ti diffused each other. The dependence of dielectric constant on temperature decreased for the sample with gradient solid solution.