Cause Analysis on Cracks of K418 High Temperature Alloy Turbine

Cracks were found on K418 high temperature alloy turbines after overrunning test, and means such as metallographic examination, chemical compositions analysis, fracture analysis and energy spectrum analysis were used to analyze the formation reason of the cracks. The result show because the investment casting mold shell was not cleaned up or the mold and the shell were not bonded tightly, material of the mold shell were involved into the liquid alloy and formed inclusions distributing along the grain boundaries during the casting process, which weakened the adhesion strength of the grain boundaries. So cracks formed along the weak grain boundaries under the action of overrunning test stress.