DLA222-007-0130 Conversion Coated Surfaces for Hypersonic Environments PHASE II Proposal

Near term fielding of Hypersonic vehicles will rely upon readily available and proven materials like refractory metals that are at an MRL of 9.  In some cases, these metals may require environmental protective coatings; these metal alloys could be based upon Tungsten (W), Niobium (Nb), or Hafnium (Hf).  Refractory materials typically survive high temperatures but oxidize under high temperatures in atmosphere.  There have been efforts to develop coatings that would help refractory metals better endure severe hypersonic flight environments.  These protective coatings have typically been deposited onto the outer surface.  The problem with deposited coatings is the preparation of the target surface and then their long term (years) storage response.  Under a Phase I, Peregrine explored the conversion coating of refractory metal surfaces; as a means to produce a surface that can resist the high temperature environments of Hypersonic flight while allowing for long term storage, increased performance and an affordable production-oriented process.  Conversion coating transforms the surface of a metal to a high temperature carbide or anodic layer.  These conversions are not “deposited” on the surface like a coating but are an integrated part of the refractory metal surface.  Using conversions versus depositions eliminates the weak link in coating systems and that is the surface preparation where poor adhesion is common. In conversion, the metal is subjected to a carburizing or anodizing process, transforming the metal and converting the exposed base metal surface. Peregrine under this proposed Phase II will develop a carburizing and/or anodizing layer on W, Nb, and Hf, to increase the high temperature resistance and duration needed for Hypersonic vehicles.  Phase I has demonstrated the feasibility of forms of these conversion coatings to provide added protection for Hypersonic flight.