Neutron radiography to detect residual core in investment cast turbine airfoils

Turbine engine blades and vanes for high-temperature applications are generally cooled by internal passages formed by the investment casting process. The cooling efficiency of the airfoil greatly depends on the removal of the ceramic core used to form the cooling passages. The detection of residual core in blades and vanes for operations above 20000F is difficult with standard visual and x-ray techniques because of the complexity of the cooling passages. A technique using neutron radiography for improved residual core detection has been developed. The contrast is enhanced by ''salting'' the ceramic core base material with a 3 percent concentration of gadolinium oxide. Commercial reactors on the west coast are used for this production inspection. Turnaround time is approximately four days. Special fixtures were designed for both shipping and inspection. Neutron radiography is now a standard production technique for high-temperature engines at Detroit Diesel Allison. Recently this inspection has been made a part of the vendor requirements