Epitaxial growth of a single-crystal nickel-based superalloy during laser melting with high-power flat-top laser

Abstract Laser-induced epitaxial growth is a prevailing technique in repair of single crystal (SX) Ni-based superalloy components. However, due to the non-uniform energy distribution of typical Gaussian laser energy profile, the nucleation and growth of stray grains are often difficult to control. In the present work, a strategy of using high-power (6 KW) flat-top laser profile is adopted to control the crystalline texture of laser melted SX Ni-based superalloy. The effect of laser exposure time on the epitaxial growth is investigated and the underlying mechanism is revealed by both experimental and finite element analysis approaches. The results show that by applying a high-power flat-top laser beam, the melting pool morphology can be effectively regulated to achieve a planar liquid/solid boundary. A longer exposure time leads to a higher G/V ratio, which in turn suppresses the deflection of grain growth within the melting pool. The computed local solidification characteristics (G/V ratio and cooling rate) reveal that favorable conditions for epitaxial growth along build direction can be achieved with the proposed strategy.