Detecting Methods And Process Of Trace Residual Ceramic Cores In Hollow Blades

In the investment casting process of turbine blade, the complicated cooling passages are formed by a ceramic core within the blade, the ceramic core is leached out after casting. The removal of ceramic core is very difficult for the extraordinary complex internal passages. Any residual ceramic core will affect the cooling of blade, which will, in turn, affect the life and safety of aircraft engines. Therefore, the detection of residual ceramic cores is very important. X-ray radiography and neutron radiography detection of residual ceramic cores were studied in this paper.HfO₂ was chosen tracer agent for the residual ceramic core detection based on the principle of X-ray detection. The effect of tracer agent on the X-ray detection of trace residual ceramic core in hollow blades was studied by mixing tracer agent into the ceramic core material. The experiment results show that the X-ray detection of residual ceramic cores was enhanced greatly by the tracer agent, and the detection of 0.2mm thick residual ceramic cores on 1.0mm thick superalloy specimens is possible for X-ray radiography when HfO2 concentration is 15%. HfOCl₂ was also chosen tagging agent for the X-ray detection, hollow blades with residual ceramic core was immersed in the saturated HfOCl2 solution and the residual ceramic cores were tagged by HfOCl₂, the blades were then X-ray radiographed. The results show that the image contrast of residual ceramic core was enhanced greatly by the tagging step. Image enhancement technique of X-ray image was also studied preliminarily, and the results of X-ray radiography were processed by using different image enhancement methods.Gd2O3 was chosen doping agent for the ceramic core material according to the principle of neutron radiography, thermal neutron radiograph was taken on Peking University 4.5 MV Von de Graff accelerator, the feasibility of neutron radiography inspection and effect of doping agent on inspection results was studied by mixing Gd2O3 into the ceramic core material. The results indicate that 0.2mm thick residual ceramic core can be easily seen on 1.0mm thick blades material at a low Gd₂O₃ concentration (2%) and the image contrast of residual ceramic core increases with the doping agent. The results of X-ray detection and thermal neutron radiography were also compared, it was found that the advantage of neutron radiography was broadly apparent compared with the X-ray radiography.