||Wright-Patterson AFB, OH 454337817
The never-ending pursuit of higher speeds, increased durability, and structural and functional efficiency under extreme conditions has pushed the current generation of propulsion and hypersonic designs to the limits of existing material systems. With metal superalloys facing reduced roles in either engine hot sections or high-speed vehicle structures, ceramic matrix composites (CMCs) and ultrahigh temperature ceramics (UHTCs) are gaining position as the next revolutionary enablers in aerospace platform performance. Since the emergence of these technologies, work in our laboratory has focused on understanding the relationships between ceramic matrix constituent development, integration, and overall component properties, while simultaneously investigating environmental effects across various length scales. This research, in particular, targets three areas in composite development.
The first is understanding and control of the molecular morphology and composition of pre-ceramic polymers- polycarbosilanes or policarbosilazanes for SiC and Si3N4 ceramics, for example, as precursors for ceramic composite constituents (fibers, matrices, and interfaces), with focus on both established and novel polymers. New chemistries and molecular structures are of interest for improved thermal and environmental durability (targeting precursors for UHTC-grade refractory metal carbides and borides), while post-synthetic modifications of existing systems (rheology, cure mechanisms and kinetics) lead to enhanced processing methods and more efficient manufacturing.
The second goal is an explanation of the property evolution of existing polymeric precursors throughout the entire thermal processing cycle. From molecular morphology, composition and weight distribution changes during low-temperature manipulations, through important mechanisms and reactive group behavior during radiative or chemical crosslinking, and finally microstructural evolution during pyrolysis and crystallization at high temperatures, knowledge of this property map allows tangible control over the performance of the ceramic product.
The third objective centers on imparting functionality on ceramic composites. Generally having a purely structural role, the extreme nature of their processing and environmental exposure (>1400°C) creates a lot of challenges toward the addition of functional elements typically found in lower-temperature material systems. Health monitoring and structural state awareness, both in- and ex-situ, are two areas in particular demand. Our studies focus on integrating a sensing network in the form of a refractory metal sub-structure within the composite, in order to add a complementary functional set of properties to those of the native ceramic. Phenomena of interest include retention of metallic properties during co-processing, chemical and structural evolution of reactive zone, integration effect on composite thermomechanical properties, and performance characterization of the integrated metallic sub-system.
Research in either of the three areas involves collaborating with a multidisciplinary team of scientists and engineers, and is be best accommodated by a strong materials or
ceramic composites; pre-ceramic polymers; structural ceramics; ceramics processing;
refractory materials; polymer synthesis; polymer chemistry; process modelling; polymer processing