Simulation of stray grain formation in Ni-base single crystal turbine blades fabricated by HRS and LMC techniques

Abstract

The simulation models of the thermal and macrostructural evolutions during directional solidification of Ni-base single crystal (SX) turbine blades under high rate solidification (HRS) and liquid metal cooling (LMC) have been constructed using ProCAST software, coupled with a 3D Cellular Automaton Finite Element (CAFE) model. The models were used to investigate the tendencies of stray grain (SG) formation in the platform region of turbine blades fabricated by HRS and LMC techniques. The results reveal that the LMC technique can prohibit SG formation by smoothing the concaved isotherm and in turn alleviating the undercooling in the platform ends to let the dendrites fill up the undercooled zone before SG nucleation. The simulation results agreed well with the experimental results, indicating that these models could be used to analyze the macrostructural evolution or to optimize process parameters to suppress SG formation. Using these models, the critical withdrawal rate for casting SX turbine blades without SG formation were determined to be around 75 μm·s-1 and 100 μm·s-1 for HRS and LMC respectively, suggesting that LMC can be used as an efficient technique in fabricating SX turbine blades without any SG defect formation.

Keywords

• thermal profile; macrostructural evolution; simulation; HRS; LMC; stray grain