THE EFFECTS OF THE INCLINATION ANGLE OF COAXIAL NOZZLE ON CRYSTAL GROWTH AND MICROSTRUCTURE FORMATION IN LASER POWDER DEPOSITION OF SINGLE-CRYSTAL SUPERALLOY

摘要

A three-dimensional mathematical model was developed to investigate the effects of inclination angle of the coaxial nozzle on crystal growth pattern and microstructure formation during laser powder deposition of single-crystal superalloy. Detailed experiments with SX nickel-based superalloy were conducted to verify the computational results. Results show that the inclination of the coaxial nozzle in the longitudinal section of deposited bead has a predominant effect on solidification conditions and corresponding microstructure formation in molten pool. The inclination of coaxial nozzle from normal direction of depositing surface delays the stray grain formation while increases the melting depth of substrate. When the inclination of coaxial nozzle toward laser scanning direction reaches 45°, the height ratio of melting depth to stray grain region exceeds 1.0, which enhances capability of the total remelting of stray grain. The simulation results and experimentally observed microstructure agree well. With the optimized processing parameters, the epitaxial columnar dendrite can grows continuously in multilayer laser powder deposition of single-crystal superalloy. These findings have some important implications for SX LPD repair processing.