Castability of high temperature alloys
Description / Outline
In the last decades, the increase in operating efficiency of gas turbines was mainly governed by the complementary approaches: a systematic alloy development in combination with the development of highly efficient cooling systems. These optimized, thin-walled blades may also lead to lower CO2 emissions and lower disc stresses. Due to a low resistance against grain boundary cracking, some alloys cannot be used for these turbomachine components.The hot tearing behavior has been studied extensively at the Chair of Metals Science and Technology using a castability test built up of two ceramic tubes mounted on a copper chill plate acting as a mould. Analogical to the well-known ring-mould test, the inner tube serves as a core. During solidification stresses arise due to the shrinkage and difference in thermal expansion. This constrained condition might lead to hot tear formation in some alloys. The crack ratio can be used to quantify the tearing resistance of an alloy.