Infiltrated Hafnium Carbonitride Protective Layers for Carbon Composite Hot Structures

The development of novel fabrication techniques to manufacture innovative hot structure architectures is important for NASA. Hot structure applications such as blunt body reentry, unpowered atmospheric flight, and powered sustained atmospheric flight at hypersonic speeds are all areas that will benefit from improved material architectures and are key in a multitude of NASA programs. Currently, hot structures are limited to 2900 deg;F for extended operation and many material systems have limited reusability. The aforementioned applications would benefit from improved hot structures that can continuously operate at temperatures above 2900 deg;F and can survive multiple flight cycles. A major barrier to realizing advanced hot structures for hypersonic flight is the development of protective coating materials compatible with carbon/carbon (C/C) substrates. Due to their high specific modulus, high fracture toughness and thermal conductivity, good thermal shock resistance, and excellent high temperature strength, advanced C/C composites are the best choice for hot structures for hypersonic flight. Unfortunately, C/C composites start to rapidly oxidize above 370 deg;C, which restricts their engineering applications in air. Current protective coatings on C/C typically fail at elevated temperatures and/or under repeated cycles due to poor bonding with C/C resulting in poor thermal conductivity between the coating and the C/C substrate. Reactive solution infiltration processing offers a means to produce integrated bond layers that are reactively fused with the C/C substrate. This effort will develop hafnium based reactive solution infiltration to form HfCN bond layers. HfCN offers a high temperature, high conductivity material solution to improve hot structure performance. This bond coat process will offer improvements over state-of-the-art coatings and enable existing high performance topcoat materials to better adhere to C/C facilitating improved reusability of hot structures.