Development of Columbium Base Alloys
Abstract
A high strength columbium alloy, Cb-28W-2Hf-O. 067C, was scaled up to 3 inch diameter ingots and processed to bar for evaluation as a potential gas-turbine bucket material. Recrystallization, grain growth and thermal-mechanical processing response were studied. To correlate structure with mechanical properties, carbide phase identity, stability and morphology were investigated. A metastable carbide phase was found, after 1700 degree C annealing, which transformed to a cubic (Cb;Hf) C1-x phase with intermediate temperature aging. Mechanical properties were measured for several structural conditions. The best low temperature ductility-high temperature creep strength combination occurred upon a 1 hour, 1700 degree C anneal after extrusion and warm swaging. This material had a 100 hour rupture strength at 1315 degree C of 25,500 psi (strength-density ratio of 68,500 inches) and room temperature elongation of 11 percent. Electron microscopy indicated that the carbide phase may strengthen this alloy by stabilizing dislocation networks. A section of as extruded bar stock was precision forged into a turbine bucket shape. Limited study of the substitution of 1 atom percent Zr for 1 atom,1 percent Hf revealed no creep strength change but the Hf alloy was more fabricable.
Document Details
- Document Type
- Technical Report
- Publication Date
- Nov 01, 1967
- Accession Number
- AD0824229
Entities
People
- J. A. Cornie
- R. C. Goodspeed
- R. T. Begley