Density-Graded and Texture-Graded Ceramics

9800257根据定义，费伯分级材料具有随位置变化的特性。该项目为单相材料的微观结构性能分级提供了一种新的手段。一种最近开发的加工方法，凝胶注模成型，其中陶瓷粉末悬浮在可聚合的液体中，形成材料。在聚合开始时，陶瓷颗粒不再能够在凝胶中自由旋转或移动，从而冻结在所需的结构中。凝胶注模过程有一个特征的“空闲时间”，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，分级密度固体将利用重力或通过离心法强化沉降而制成。预计根据工程应用的要求，这些材料可以被配置为具有致密、耐磨的表面，或多孔的、允许缺陷的表面。氧化铝以其硬度和化学惰性而闻名，是分级密度固体的模型。其次，通过在磁场梯度中进行凝胶注模，可以得到具有梯度结构的固体。六方亚铁磁体--六角铁氧体，由于其高的磁各向异性，将被织构分级。由于其结晶学织构与形态织构相结合，预计钡铁氧体的机械性能也会有梯度。场辅助渐变技术适用于铁磁体、顺磁体和铁电和顺电材料，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)来模拟实际的微结构。模拟工作将与美国国家标准与技术研究所联合进行。模拟和实验结果将构成密度和织构梯度固体材料设计的基础。%由于陶瓷被考虑用于更复杂和更复杂的应用，一个组件必须具有多种功能，并满足看似不同的材料要求。相互冲突的材料需求迫切需要分级的微结构。近年来，梯度功能材料受到了相当大的重视。本项目将探索一种新的材料级配方法和新的级配结构，为材料工程师提供一种低成本、可重复使用的功能梯度材料生产方法。***

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. ***