Influences of Cooling Conditions on the Liquation Cracking in Laser Metal Deposition of a Directionally Solidified Superalloy

Directionally solidified (DS) nickel-based superalloys are widely used in manufacturing turbine blades, which may fail due to wear and/or material loss during service. Laser metal deposition (LMD) has been considered to be a promising technology in repairing the damaged components thanks to the high temperature gradient formed, which is conducive to the growth of directional microstructure. Intergranular liquation cracking in the heat-affected zone (HAZ) has been one of the major problems in LMD of the DS superalloys. In this paper, the influences of two cooling conditions (conventional cooling and forced cooling) on the microstructure development and liquation cracks were studied for the laser deposition of a DS superalloy IC10. The experimental results showed that, as compared to the conventional cooling, both number and length of the liquation cracks in HAZ were notably reduced under the forced cooling condition. The effects of cooling conditions on temperature and stress fields were analyzed through a thermo-elastoplastic finite element analysis. It was revealed that the maximum tensile stress and high tensile stress region in the substrate were effectively minimized while using the forced cooling measure. The forced cooling on the substrates is a promising method for mitigating the liquation cracking in LMD of DS superalloys.