Microstructure and Mechanical Properties of Repaired Joint on Single Crystal Superalloy Using Laser Metal Deposition

DD6 single crystal superalloy was repaired by laser metal deposition (LMD). The microstructural characteristics and mechanical properties of the single crystal superalloy base metal and laser repaired joint were studied by optical microscopy, scanning electron microscopy, and microhardness testing. The results show that the microstructure of the laser repaired area is directionally-solidified columnar crystal with epitaxial growth. It is composed of γ-phase matrix and a small number of intergranular MC-type carbides. The microstructure and phase composition of the heat-affected zone (HAZ) of DD6 single crystal superalloy are similar to those of the base metal, but the size of γ′ phase in HAZ is smaller (≤0.2 μm) and the ratio of γ′/γ decreases obviously. After laser metal deposition repair, the microhardness of the laser repaired area is up to 450~470 HV, significantly higher than that of DD6 single crystal superalloy base metal, indicating that the repaired area has better wear resistance.