Silicide Coatings on Refractory Metal Alloys for High Temperature Oxidation Protection of Hypersonic Vehicle Leading Edges

Many hypersonic vehicle components utilize high temperature alloys. Metal alloys have found use in these applications because of their high melting point and excellent high temperature strength. To date, conventional oxidation-protective coatings have provided sufficient oxidation protection to the alloys. However, as vehicle performance advances, the metallic components will be exposed to operating environments that far exceed the capabilities of conventional oxidation protection coatings. To enable the next generation of metallic components for vehicle applications, new oxidation-protective coating systems are required to protect the alloys from oxidation at very high temperatures. In Phase I, Ultramet developed a process to form a conformal, dense, and highly adhered coating. Thermal shock testing using an oxyacetylene torch showed that the coating was retained, with no cracking or thermal shock damage, and that a protective oxide layer was developed on the surface. Ultramet's STTR research institution partner initiated development of a high temperature oxidation model for coatings to predict oxide formation, oxide shear thinning, and ultimately coating recession. A one-dimensional model was developed to capture the transport of mass, momentum, and energy in coatings undergoing phase transformation and shear thinning in an oxidizing environment. The model was used to generate temperature and material recession results for a two-phase material system. The results indicated linear and non-linear temperature dependence depending on phase. Through mesh movement, the recession of the material was tracked with respect to temperature and time. In Phase II, Ultramet will continue to develop and optimize the coating process, including further exploration of processing conditions and scaleup to coating of subscale components. Ultramet will continue to collaborate with its STTR research institution partner to expand the 1D model initially developed in Phase I to a two-dimensional domain. The model will be validated through testing that will evaluate the coating in relevant operating environments, examining oxide formation, oxide shear thinning, and coating recession. The validated model will be used to inform further optimization of processing methods at Ultramet. The combined efforts will identify the upper boundary of the operating envelope of coatings, which will support faster progression of the coating system TRL toward program insertion. Approved for Public Release | 25-MDA-12052 (27 Mar 25)