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

这项拟议研究的目的是提供资金，以成熟一种名为CeraSGel的新工艺，通过该工艺可以制造出具有定向短纤维相的复杂几何形状的陶瓷。该工艺适用于任何可以无压烧结的粉末系统，但对于本研究，我们选择了一种有前途的超高温材料，即二硼化锆或具有SiC短纤维的ZrB 2。 CeraSGel涉及将亚微米陶瓷粉末和短切纤维悬浮在通过将少量聚合物溶解在水中产生的凝胶中，以提供陶瓷混合物的可成形性。纤维相通过局部剪切应力定向，所述局部剪切应力是在将旋转阳模插入陶瓷/聚合物混合物中时产生的。纤维相增强了陶瓷基质相的强度和韧性，并且无压烧结提供了低成本的制造方法。在这个项目中，我们将：（1）表征聚合物对成型，粘合剂燃尽和最终部件密度的作用。(2)确定聚合物与ZrB 2和SiC相在湿态和干态下的相互作用。(3)优化绿色坯体的烧结条件，包括聚合物负载、纤维取向、烧结温度和时间对SiC增强ZrB 2的密度、微观结构和机械性能的影响。发动机进气道、火箭喷管插入件和高速航空表面的鼻盖是需要形状复杂的高温部件的特殊应用。虽然存在满足这些应用的苛刻温度要求的材料，但加工和成形成本通常非常高和/或部件的机械性能不足以满足预期的应用。在最广泛的意义上，拟议的工作将开发一个普遍适用的成型工艺，使复杂的零件可以生产定向强化或增韧相。该工艺是廉价的，因为它适合于现代复合材料制造技术，并且最小化昂贵的材料损失和加工，因为可以制造近净形部件。

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.