Ceramic shell moulds for investment casting of low-pressure turbine rotor blisk

The investment casting process was adopted to cast a low-pressure turbine rotor (LPTR) blisk. The casting was carried out in vacuum at 1525 °C by using BZL12Y superalloy. Ceramic shell moulds for the casting were prepared by two different fillers (mullite and zircon), two types of colloidal silica binders (polymer-free binder-A and polymer-containing binder-B) and cobalt aluminate solution. The shell specimens having binder B showed improved green strength and self-load sag resistance in comparison to their counterparts having binder-A. Samples prepared from the slurry compositions having binder-A showed higher residual fired strength than the samples prepared from slurry compositions having binder-B. Defect-free castings of LPTR blisks with fine equiaxed grains were obtained by using ceramic shell moulds containing binder-B and cobalt aluminate solution. The LPTR blisks cast from the ceramic shell moulds having binder-A showed hot tear defect along-with coarse grains. Irrespective of the filler, the LPTR blisk cast by using ceramic shell moulds and cobalt aluminate showed fine grains. The average surface roughness values of LPTR blisks cast from ceramic shell moulds, having binder-B and binder-A, were observed to be in the acceptable range even though castings with binder-A showed marginally lower surface roughness.