Investigation of on-site repair of 18Ni300 by underwater laser direct metal deposition technique

Abstract

The deep-sea pressure-resistant material 18Ni300 was repaired by underwater laser direct metal deposition (UDMD) technique with various processing parameters in a simulated 30 m underwater environment. The microstructure and mechanical properties of the as-repaired samples were systematically characterized. The results were compared with those of the samples repaired by in-air laser direct metal deposition (DMD). Results showed that the cellular microstructure was formed in the samples repaired by UDMD. The lath martensite in the cellular microstructure was fine and the dislocation density was high in the samples repaired by UDMD in comparison with those in the sample repaired by DMD due to the water quenching effect involved in the UDMD process. Precipitation behavior of intermetallic compounds was not observed in the repaired areas of 18Ni300 due to the short time for intrinsic heat treatment. A number of fine oxide particles were observed in the repaired areas of the samples repaired by UDMD and the number of oxide particles increased with increasing cooling rate. The increase of laser energy density led to the decrease of tensile strengths and increase of impact absorbed energies of the samples repaired by UDMD. The samples repaired by DMD and UDMD using the same processing parameters exhibited equivalent tensile properties, while the impact absorbed energy of the sample repaired by UDMD was lower than that of the sample repaired by DMD. Moreover, laser remelting treatment could significantly increase the tensile properties of the samples repaired by UDMD.