Effect of Process Parameters on Pulsed-Laser Repair of a Directionally Solidified Superalloy

Abstract

Directionally solidified nickel-based superalloy GTD-111 was repaired using pulsed Nd:YAG laser powder deposition (PLPD). A test matrix was created and tested to link deposit and defect formation to process parameters. Epitaxial solidification of the deposit was achieved. The grain size was uniform throughout multiple layers of deposit and appeared to be of cellular dendritic morphology. The crack formation is associated with the “stray” grains, which seem to be controlled by the geometry and overlap of the deposits. The formation of stray grains tended to be suppressed in deposits with shallow and wide profiles with smooth toe transitions into previous beads. Geometric discontinuity and formation of stray grains were found to contribute significantly to the formation of microfissures at the weld toes. Multiple pulses were found to remelt and heal the microfissures in the previous spot deposit. With optimized process parameters, crack-free, multiple-layered, deposits were achieved for tip repair (top-down orientation) of GTD-111 blades with Rene 80 and IN625 filler metals.