Ultra High Temperature Ceramics (UHTC) coatings
An Italian large enterprise with a solid expertise on projects in which materials, technology and innovation play a critical role, has carried out manufacturing activities to deposit UHTC (Ultra High Temperature Ceramics) on highly stressed space components. The technology (material and deposition process) herein described offers thermal protection in extreme conditions such as applications where oxidation and/or erosion resistance at high temperature are required.
The need to reduce space missions’ costs has led to the design of Reusable Spatial Vehicle (RLV), capable of performing a large number of missions without performing, or partially performing, the exhausting as well as expensive maintenance operations which are currently needed by the space vehicles after the atmospheric re-entry. This has led the research towards the study and experimentation of advanced materials that, besides having high melting temperatures, have good structural characteristics at temperatures greater than 2000 K, far exceeding the conditions that are sustainable by conventional materials. Therefore, within the framework of the Project “ASA - Advanced Structural Assembly” sponsored by the Italian Space Agency (ASI), the provider has carried out manufacturing activities to deposit UHTC (Ultra High Temperature Ceramics) on a WLE (Wing Leading Edge) component. This component has been tested in simulated flight conditions in a Plasma Wind Tunnel facility. UHTC are ceramic composite materials. The matrix of these composite materials is generally constituted by high melting diboride or carbide (TiB2, ZrB2, HfB2, HfC). Within the matrix, particles of other ceramic phases - carbides (SiC, ZrC), silicides (MoSi2, TaSi2), or nitrides (Si3N4) - are dispersed. The matrix provides mechanical resistance, whilst the dispersed ceramic particles improve oxidation resistance. The particles act also as sintering aids by decreasing the processing temperature. Within the ASA project, the owner of the technology developed an expert know-how in the realisation of UHTC coatings, both under the manufacturing and the deposition process perspective, that could be applied to provide thermal protection in extreme conditions such as applications where oxidation and/or erosion resistance at high temperature are required. An example of this application could be industrial furnaces or nuclear plants.
Innovations & Advantages
A proper multilayer coating process has been developed consisting on the deposition of: • a thin layer, for adhesion improvement • a mixture of borides – carbides – silicides, for a flexible design of coating properties UHTC coatings offer thermal protection in extreme conditions such as applications where oxidation and/or erosion resistance at high temperature (up to 2000 °C) are required (eg. thermal protection systems for re-entry vehicles). Nevertheless, the use of massive ceramics in large and hot structures, such as the wing leading edges or nose cap of re-entry vehicles, is strongly limited by the intrinsic brittleness of these materials and by the difficulty in manufacturing (sintering and machining) large ceramic components. The owner of the technology has developed an optimised deposition process that allows the realisation on thick coating (some hundred microns). The use of such UHTC coatings to protect the surface from the oxidizing and erosive environment, deposited on tough and heat resistant substrates, can guarantee a good overall reliability of the hot structure.
Current and Potential Domains of Application
UHTC coatings offer thermal protection in extreme conditions such as applications where oxidation and/or erosion resistance at high temperature (up to 2000 °C) are required (eg. thermal protection systems for re-entry vehicles or ipersonic vehicles). Due to their properties, UHTC coatings can find some applications in fields not related to space where high temperature and oxidation resistance is the dominant factor. For example, due also to their refractory properties, they may be used in nuclear applications and in industrial furnaces.