Investigation of the Feasibility of Producing Tungsten-Hafnium Carbide Alloy by Powder Metallurgical Techniques.

摘要

By virtue of its excellent elevated temperature strength, the W-0.35HfC alloy is a candidate air vane leading edge material for hypersonic missile application. Because of difficulties associated with arc melting and extrusion of large ingots of this alloy, the feasibility of producing material by powder metallurgy techniques with mechanical properties equivalent to arc cast material was investigated. Three consolidation approaches were evaluated. In Process A, deoxidized tungsten powder was blended with hafnium hydride and graphite powder, encapsulated in mild steel cannisters, and dehydrided under vacuum at elevated temperature. In Process B, deoxidized tungsten powder was blended with degassed hafnium carbide, encapsulated in mild steel cannisters, and evacuated. In Process C, prealloyed W-0.35HfC powder was encapsulated in mild steel cannisters and hydrogen deoxidized at elevated temperatures followed by evacuation. Process A and B powders were consolidated by extrusion at 2300 F. The resulting materials had oxygen levels and controlled carbon levels comparable to arc cast material. Mechanical properties of these materials did not approach those of arc cast material due to incomplete densification and incomplete homogenization of the HfC. Additional thermal-mechanical processing appears to be necessary to improve mechanical properties. The prealloyed WHfC powder, Process C, could not be extruded at 2300 F. However, the material was successfully extruded at 3600 F and had tensile strength equivalent to arc cast material.