Investment Casting of Columbium Alloys

The state of the art of columbium alloy investment castings has been advanced. In addition to demonstration of castability of four different alloys, the cast material itself has been characterized with respect to microstructure, alloy segregation, weldability, and the effect of heat treatment. Based upon a number of alloy selection criteria, one of the alloys, C-103, was chosen for more detailed investigation including casting of solid and cored turbine vanes having a wall thickness as low as 0.040 in. Heat treatment parameters were established for optimization of C-103 mechanical properties including post-weld heat treatment. Under some casting conditions, the as-cast mechanical properties are equivalent to wrought properties. Heat treatment improves particularly ductility, and restores properties after welding. Chemistry, mechanical property, and economic considerations of material recycle are discussed. A tentative specification has been written covering C-103 castings incorporating producibility and material characterization available to date.