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

普通陶瓷的热膨胀通常比金属的低。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，从而导致复合材料的断裂。为了避免这种失败，出现了一种使用功能梯度材料(FGM)的新技术，其特征是材料的性能从一个表面到另一个表面连续变化。这种材料是通过形成具有预定成分分布的由陶瓷和金属组成的复合层的堆来制备的。在本研究中，通过在单一陶瓷体中形成一系列固溶体来制备功能梯度材料。首先，从霞石固溶体(Na_&lt；1-x&Gt；M_xAlSiO_4：M=Li和K)制备了热膨胀功能梯度材料。通过烧结由NaAlSiO_4粉末和{(1-x)NaAlSiO_4+xMAlSiO_4(M=Li和K)}混合粉末组成的绿色致密层，它们结合在一起形成梯度固溶体，其成分随界面的距离而连续变化。霞石固溶体具有与金属相同的高热膨胀系数。当x=0.15时，Na_&lt；1-x&gt；Li_xAlSiO_4Li_xAlSiO_4的热膨胀系数从1.6x10^&lt；-5&gt；/ﾟC下降到1.2x10^&lt；-5&gt；/ﾟC，当x=0.43时，随着x的增加，梯度固溶体的热膨胀系数随固溶体成分的增加而逐渐增大，从而使梯度固溶体的热膨胀系数随固溶体成分的增加而逐渐变化。其次，研究了一种功能梯度材料的电学性质。通过烧结PZT(A)和PZT(B)的层状压坯，使PZT(A)和PZT(B)相互接触并相互扩散，在单一的陶瓷体中形成了一系列PbZrxTi1-x&gt；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减小。

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.