Thermal coatings for titanium-aluminum alloys
Titanium aluminides and titanium alloys are candidate materials for use in hot structure and heat-shield components of hypersonic vehicles because of their good strength-to-weight characteristics at elevated temperature. However, in order to utilize their maximum temperature capability, they must be coated to resist oxidation and to have a high total remittance. Also, surface catalysis for recombination of dissociated species in the aerodynamic boundary layer must be minimized. Very thin chemical vapor deposition (CVD) coatings are attractive candidates for this application because of durability and very light weight. To demonstrate this concept, coatings of boron-silicon and aluminum-boron-silicon compositions were applied to the titanium-aluminides alpha2 (Ti-14Al-21Nb), super-alpha2 (Ti-14Al-23-Nb-2V), and gamma (Ti-33Al-6Nb-1Ta) and to the titanium alloy beta-21S (Ti-15Mo-3Al-3Nb-0.2Si). Coated specimens of each alloy were subjected to a set of simulated hypersonic vehicle environmental tests to determine their properties of oxidation resistance, surface catalysis, radiative emittance, and thermal shock resistance. Surface catalysis results should be viewed as relative performance only of the several coating-alloy combinations tested under the specific environmental conditions of the LaRC Hypersonic Materials Environmental Test System (HYMETS) arc-plasma-heated hypersonic wind tunnel. Tests were also conducted to evaluate the hydrogen transport properties of the coatings and any effects of the coating processing itself on fatigue life of the base alloys. Results are presented for three types of coatings, which are as follows: (1) a single layer boron silicon coating, (2) a single layer aluminum-boron-silicon coating, and (3) a multilayer coating consisting of an aluminum-boron-silicon sublayer with a boron-silicon outer layer.
- Research Organization:
- National Aeronautics and Space Administration, Hampton, VA (United States). Langley Research Center
- OSTI ID:
- 6467783
- Report Number(s):
- N-93-26048; NASA-TM-107760; NAS-1.15:107760; CNN: RTOP 506-73-43-01
- Country of Publication:
- United States
- Language:
- English
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Related Subjects
ALUMINIUM
PROTECTIVE COATINGS
BORON
SILICON
TITANIUM ALLOYS
SURFACE COATING
CATALYSIS
CHEMICAL VAPOR DEPOSITION
FATIGUE
HYDROGEN
OXIDATION
PERFORMANCE
THERMAL SHIELDS
THERMAL SHOCK
ALLOYS
CHEMICAL COATING
CHEMICAL REACTIONS
COATINGS
DEPOSITION
ELEMENTS
MECHANICAL PROPERTIES
METALS
NONMETALS
SEMIMETALS
SHIELDS
360101* - Metals & Alloys- Preparation & Fabrication