Design and Manufacture of Ultra-High Temperature Ceramics with Oriented Strengthening and Toughening Phases

这项拟议研究的目的是为成熟一种称为CeraSGel的新工艺提供资金，通过该工艺可以制造具有定向短纤维相增强的复杂几何形状的陶瓷。该工艺适用于任何可加压烧结的粉末体系，但在本研究中，我们选择了一种很有前途的超高温材料，即二硼化锆或具有短纤维SiC的ZrB2。CeraSGel是将亚微米陶瓷粉末和切碎的纤维悬浮在一种凝胶中，这种凝胶是通过将少量聚合物溶解在水中产生的，以提供陶瓷混合物的可成形性。当纺丝模插入陶瓷/聚合物混合物时，纤维相由局部剪切应力定向。纤维相提高了陶瓷基体相的强度和韧性，无压烧结提供了一种低成本的制造方法。在这个项目中，我们将：(1)表征聚合物对最终零件的形成、粘结剂燃尽和密度的作用。(2)测定聚合物在湿态和干态下与ZrB2和SiC相的相互作用。(3)优化绿体烧结条件，包括聚合物载荷、纤维取向、烧结温度和时间对SiC增强ZrB2的密度、微观结构和力学性能的影响。发动机整流罩进气道、火箭喷管插入件和高速航空航天表面的鼻盖是需要复杂形状、高温部件的特殊应用。虽然存在满足这些应用苛刻温度要求的材料，但加工和成型成本通常非常高，并且/或部件的机械性能不足以满足预期应用。从最广泛的意义上讲，所提出的工作将开发一种普遍适用的成形工艺，从而可以生产具有定向强化或增韧阶段的复杂零件。该工艺价格低廉，因为它适用于现代复合材料制造技术，并最大限度地减少昂贵的材料损失和加工，因为可以制造接近净形状的部件。

The objective of this proposed research is to provide funding to mature a new process called CeraSGel by which complex geometries of ceramic reinforced with oriented short-fiber phases can be manufactured. The process is applicable to any powder system that can be pressurelessly sintered, but for this study we have chosen a promising ultra-high temperature material, i.e. zirconium diboride or ZrB2 with short fibers of SiC. CeraSGel involves suspending submicron ceramic powders and chopped fibers in a gel created by dissolving small amounts polymer in water to provide formability of the ceramic mixture. Fiber phases are oriented by local shear-stresses that result when a spinning male mold is inserted into the ceramic/polymer mixture . The fiber phase enhances the strength and toughness of the ceramic matrix phase and pressureless sintering affords a low-cost manufacturing approach. In this project we will: (1) Characterize the role of the polymer on the formation, binder burnout, and density of the final part. (2) Determine the interaction of the polymer with the ZrB2 and SiC phases in the wet and dry states. (3) Optimize sintering conditions for green bodies including the effect of polymer loading, fiber orientation, and sintering temperature and time on density, microstructure, and mechanical properties of SiC reinforced ZrB2. Engine cowl inlets, rocket nozzle inserts, and nose-caps in high-speed aerospace surfaces are particular applications where complex-shaped, high-temperature components are required. While materials exist that meet the demanding temperature requirements for these applications, processing and forming costs are often very high and/or the mechanical properties of components are insufficient for the intended applications. In the broadest sense, the proposed work will develop a generally applicable forming process whereby complex parts can be produced with oriented strengthening or toughening phases. The process is inexpensive, as it is amenable to modern composite fabrication techniques, and minimizes expensive material losses and machining as near net-shape components can be fabricated.