Density-Graded and Texture-Graded Ceramics

小行星9800257 根据定义，梯度材料具有随位置而变化的特性。 该项目提供了一种新的手段，单相材料的性能微观分级。 最近开发的一种加工方法，凝胶注模法，其中陶瓷粉末悬浮在可聚合液体中用于形成材料。 在聚合开始时，陶瓷颗粒不再自由旋转或在凝胶中移动，因此“冻结”在所需的结构中。 凝胶注模工艺具有特征性的“空闲时间”，其定义为聚合和凝胶化之前的时间。利用该空闲时间允许微结构的分级。 该项目将利用闲置时间以两种方式对单相氧化物进行分级。 首先，梯度密度固体将通过利用重力或通过离心作用增强沉降来制造。 预期这些材料可以被配置为具有致密的耐磨表面或多孔的耐缺陷表面，如工程应用所要求的。 氧化铝以其硬度和化学惰性而闻名，是密度梯度固体的模型。 第二，梯度纹理固体将通过在磁场梯度中进行凝胶注模来生产。 六方亚铁磁性钡六角铁氧体由于其高磁各向异性，将被纹理分级。由于其晶体学织构与形态学织构相结合，钡铁氧体也有望在机械性能方面具有梯度。 场辅助分级技术适用于铁磁体、顺磁体以及铁电体和顺电体，后者在电场梯度中。这些固体的性质将使用面向对象的有限元程序（OOF）的实际微观结构进行模拟。 模拟工作将与国家标准和技术研究所一起进行。 模拟与实验结果相结合将形成密度和纹理梯度固体材料设计的基础。 由于陶瓷被认为是更复杂和复杂的应用，一个组件必须提供多种功能，并满足看似不同的材料要求。 涂层材料要求具有梯度组织。 梯度功能材料是近年来研究的热点。 该项目将探索一种新的材料分级方法和新的分级结构，为材料工程师提供一种低成本，可重复的生产功能梯度材料的方法。 ***

9800257 Faber Graded materials, by definition, have properties that vary as a function of position. This project offers a novel means to microstructurally grade the properties of single-phase materials. A recently-developed processing method, gelcasting, in which ceramic powders are suspended in a polymerizable liquid is used to form the material. At the onset of polymerization, the ceramic particles are no longer free to rotate or move in the gel, thus "freezing in" the desired structure. The gelcasting process has a characteristic "idle time" defined as the time prior to polymerization and gelation. Taking advantage of that idle time allows for gradation of the microstructure. The project will use the idle time to grade single phase oxides in two ways. First, graded-density solids will be made by making use of gravity or enhanced settling through centrifugation. It is anticipated that these materials can be configured to have dense, wear-resistant surfaces, or porous, flaw tolerant surfaces, as demanded by the engineering application. Aluminum oxide known for its hardness and chemical inertness is the model graded-density solid. Second, graded-texture solids will be produced by performing gelcasting in a magnetic field gradient. The hexagonal ferrimagnetic, barium hexaferrite, will be texture-graded due to its high magnetic anisotropy. Since its crystallographic texture is coupled to morphological texture, barium ferrite is also expected to have gradients in mechanical properties. The field-assisted gradation technique is applicable to ferromagnets, paramagnets, and ferro- and paraelectrics, the latter in an electrical field gradient. The properties of these solids will be simulated using an object oriented finite element program (OOF) for actual microstructures. The simulation work will be done in conjunction with the National Institute of Standards and Technology. Simulations coupled with experimental findings will form the basis for materia ls design of density- and texture-graded solids. %%% As ceramics are considered for more complex and sophisticated applications, one component must serve several functions and meet seemingly disparate materials requirements. Conflicting materials requirements beg for graded microstructures. Considerable emphasis has been placed on functionally gradient materials in recent years. This project will explore a new method for grading materials and novel gradation architectures, that may provide materials engineers with a low-cost, reproducible method of producing functionally gradient materials. ***