Density-Graded and Texture-Graded Ceramics

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分级提供了一种新的方法。最近发展的一种加工方法，凝胶铸造，其中陶瓷粉末悬浮在可聚合的液体中被用来形成材料。在聚合开始时，陶瓷颗粒不再在凝胶中自由旋转或移动，因此“冻结”在所需的结构中。凝胶浇注过程具有一个特征“空闲时间”，定义为聚合和凝胶之前的时间。利用空闲时间可以实现微观结构的分级。该项目将利用空闲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加强沉降通过离心。根据工程应用的要求，预计这些材料可以配置为具有致密、耐磨的表面，或多孔、耐缺陷的表面。氧化铝以其硬度和化学惰性而闻名，是典型的分级密度固体。其次，通过在磁场梯度中进行凝胶铸造，将产生渐变纹理固体。六铁氧体钡由于其高的磁各向异性而具有织构梯度。由于其晶体结构与形态结构耦合，铁氧体钡在力学性能上也有望具有梯度。场辅助梯度技术适用于铁磁体、顺磁体以及铁和准电体，后者处于电场梯度中。这些固体的性质将使用面向对象的有限元程序（OOF）来模拟实际的微观结构。模拟工作将与国家标准与技术研究所共同完成。与实验结果相结合的模拟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精密的应用，一个组件必须具有多种功能，并满足看似不同的材料要求。相互矛盾的材料要求要求有梯度的微观结构。近年来，功能梯度材料受到了广泛的关注。该项目将探索一种新的材料分级方法和新颖的分级结构，这可能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. ***