Fabrication of Porous Ultra-high Temperature Ceramics for Transpiration Cooling of Hypersonic Vehicles.

Lead Research Organisation: Imperial College London
Department Name: Materials

Abstract

Ultra-high temperature ceramics (UHTCs) are to be examined for their use in transpiration cooling systems for the leading edges of hypersonic vehicles. Previous thermal protection systems (TPS) for applications such as atmospheric re-entry have tried to minimise the effect of aerodynamic heating by having a large radius of curvature for the leading edge [1]. This is effective at reducing the heating of the vehicle but is detrimental to manoeuvrability. These shields would also rely on ablative cooling, a process by which the protective material is removed, effectively removing heat from the protected vehicle but is only suitable for single use [1].

To design a sharp leading edge, which is also reusable, the TPS must be able to withstand up to 2000C without sustaining damage. Only UHTCs are capable of sustaining such temperatures [2]. The TPS to be tested is transpiration cooling, a process by which a cooling gas flows through the exposed outer layer. This both cools the material internally and provides a protective fluid layer at the surface [1].

Transpiration cooling requires a material that allows for fluid flow while maintaining structural stability, the fabrication of which will be the primary focus of the current work. Different methods for creating internal channels in zirconium diboride will be assessed. Currently the creation of porous zirconium diboride by partial sintering has been shown to allow for sufficient fluid flow for transpiration cooling [1]. Following work will now be to probe parameters controlling coarsening and densification of zirconium diboride, with the aim to produce a porous material which will not then densify at application temperatures of 2000C. Characterisation of materials will involve use of dilatometry to assess densification at high temperature, while material properties such as thermal conductivity, strength, and permeability will be used to assess suitability of materials.

Additionally, work will involve combining the porous skin with a dense, channelled, substructure for efficient and controlled delivery of cooling fluid, as well as providing structural reinforcement. Also made from zirconium diboride, optimisation of channel size and spacing will be investigated. Manufacturing methods such as pressureless sintering, robocasting, and gel casting are to be assessed for their suitability for the design and development of an effective transpiration cooling system.

[1] Rocher, M.E, et al., "Testing a Transpiration Cooled Zirconium-Di-Boride sample in the Plasma Tunnel at IRS." AIAA Scitech 2019 Forum, 2019.
[2] Fahrenholtz, W.G, & Hilmans, G.E. "Ultra-high Temperature Ceramics: Materials for extreme environments." Scripta Materialia, 129, 94-99 2018.

Publications

10 25 50

Studentship Projects

Project Reference Relationship Related To Start End Student Name
EP/N509486/1 01/10/2016 30/09/2021
2131760 Studentship EP/N509486/1 29/09/2018 31/03/2022 Rowan Hedgecock
EP/R513052/1 01/10/2018 30/09/2023
2131760 Studentship EP/R513052/1 29/09/2018 31/03/2022 Rowan Hedgecock