Microstructural studies of direct-laser-deposited stainless steel 316L-Si on 316L base material

Microstructure and hardness of SS316L-Si deposited by direct laser deposition (DLD) on a conventional SS316L base material are studied. The DLD process produced a crack-free metallic part with a density of ~ 99.5%. The as-deposited samples exhibit a microstructure with millimetre-sized solidified melt pools. They consist mainly of columnar dendrites which were formed preferentially along < 001 > direction, generating solidification texture and columnar grains. Dendrites with cellular morphology were also formed in regions of higher solidification rates, mainly above the localized heat-affected zone in the layers. The deposited SS316L-Si contains a primary austenitic matrix and secondary δ-ferrite in the interdendritic regions. The average hardness measured along parallel and normal surfaces with respect to the building direction is nearly the same (~ 185 HV), indicating homogeneity in the microstructure of the as-deposited SS316L-Si along the two orthogonal surfaces. The analysis of microstructure, defects and intermetallic phases was carried out using optical microscopy, scanning electron microscopy and transmission electron microscopy.