characterization and investigation of grain selection in spiral grain selectors during casting single-crystal turbine blades

manufactured single crystal components using ni-base super alloys are routinely used in the hotsections of aero engines and industrial gas turbines due to their outstanding high temperaturestrength, toughness and resistance to degradation in corrosive and oxidative environments. tocontrol the quality of the single crystal turbine blades, particular attention has been paid to grainselection, which is used to obtain the single crystal morphology from a plethora of columnar grains.for this purpose, different designs of grain selectors are employed and the most common type is thespiral grain selector. a typical spiral grain selector includes a starter block and a spiral (helix)located above. it has been found that the grains with orientation well aligned to the thermal gradientsurvive in the starter block by competitive grain growth while the selection of the single crystalgrain occurs in the spiral part. in the present study, 2dspiral selectors with different geometrieswere designed and produced using a state-of-the-art bridgeman directional solidification castingfurnace to investigate the competitive growth during grain selection in 2d grain selectors. theprincipal advantage of using a 2-dselector is to facilitate the wax injection process in investmentcasting by enabling significant degree of automation. the directional solidification process forobtaining single crystal component for nickel super alloys based on the competitive growth in 2dand 3d single crystal grain selector was experimentally investigated for various geometries.transverse sections of the grain selectors using optical and ebsd microscopy techniques wereobserved to understand the competitive grain growth process.