Non-Carbon Based Thermal Protection Systems for Hypersonic Fliers

Overview

Because current carbide thermal protection system materials, at hypersonic speeds, can ablate and form carbide compounds that can reduce thermal and mechanical properties and make the craft they are on more detectible; our team was tasked with the development of a non-carbon based thermal protection system. Thermal protection systems are material systems that are designed to protect a flying craft from the extreme temperatures and pressures that exist in hypersonic environments. Zirconium Diboride produce via Spark Plasma Sintering (SPS or FAST) was chosen as the non carbon based TPS we would investigate.

Objectives

-Research and Identify candidate materials

-Down Select those materials based on material properties and cost quality metrics

-complete CFD analysis via ANSYS on a hypersonic flier geometry

-Determine the best method for the manufacturing of the test material

-Procure precursor materials and produce a prototype test object

-test materials properties, (thermal resistance, oxidation resistance, density, particle size distribution, XRD spectra)

-compare those properties to preexisting carbon based thermal protection systems

Approach

-Extensive research was conducted on the development of a proper fluid flow model for a set of conical shape hypersonic geometries that were provided to us by Arfield, density flow models and temperature models were developed which help evaluate the temperatures that the material might endure in flight

-Researched a series of 9 material candidates and tabulated and compared their properties via a QFD chart

-Selected one material candidate (ZrB2) to move forward with to production and testing

-acquired ZrB2 powder and used it to produce a 20mm by 5 mm cylindrical test puck via spark plasma sintering, the powder was then tested for its particle size distribution and X ray spectra

-this material was then tested for its density, high temperature oxidation behavior (via TGA), XRD spectra, and microstructure via SEM

-The results of those tests were then compared to common carbon-based thermal protection systems, namely silicon carbide

Outcomes

ANSYS simulations proved to be accurate enough for the premise of this project, although, a chemical model needs to be added in order for it be most accurate, this is something that will be worked on in future installments of this project.

XRD comparison of the powder and the finished ceramic confirmed that no additional phases form in this sintering process, this is ideal in that the formation of new phases may change the material properties of the coating and make it less ideal for the given application.

Powder size distribution shows a bimodal pore size distribution. Which is ideal in that, when the particles are packed together, the smaller particles will occupy the interstices left by the bigger particles, thus resulting in greater densification.

Initial density testing of the material showed that it was significantly less dense than what was expected of it to be under the sintering conditions used from literature. This may be because of some property of the powder or of the die used, if we were to manufacture a test puck again, the time of the sintering step should be increased by 30-40 minutes to ensure that proper densification occurs. This lack of density effected most other property measurements, including the oxidation resistance measurement, which gave a result that was below the theoretical for ZrB2, and therefore made it preform worse compared to SiC in that regard.

From the materials side of this project, overall, ZrB2 still shows promise as a thermal protection system, this is because the density of the ceramic is something that can easily be manipulated before manufacturing. We also believe that an increase in density would dramatically improve oxidation resistance and most overall properties. Additionally, SPS shows great promise for the manufacturing of TPS’s as the shapes it can produce are only limited by the size and shape of the die used.