Microstructural and mechanical behaviour of friction welded SS316L components fabricated by selective laser melting

The research study on solid state welding, especially rotary friction welding (FW) on the selective laser melted (SLM) components is limited. The present study is performed to deduce the scope of FW on SLM stainless steel (SS) 316 L parts and also to understand the plastic deformation effect on SLM components. The obtained results can be considered as a reference for the dissimilar welding joints of SS316L with other metallic systems in future studies. The microstructural analysis revealed significant changes in microstructural features like grain morphology and grain orientation. Also, it showed the conventional three distinct zones during the FW process, viz., base metal (BM), heat affected zone (HAZ) and weld zone (WZ). The columnar grains in the BM change into elongated deformed grains while moving towards the WZ. The findings also confirmed the existence of homogeneous equiaxed grains due to complete recrystallization in the WZ. The refined grains, resulted in improved hardness by 23 % at the WZ, when compared with SLM sample. Tensile test results demonstrated an enhancement of yield strength of about 190 MPa, however by sacrificing the ductility. WZ has achieved higher hardness and strength than the SLM component, even though the dislocation density is very high in later one. To understand this coupled effect, work hardening calculations and strengthening contributions were evaluated. The results from strengthening mechanisms confirmed that Hall-Petch strengthening is the dominant strengthening contribution in the welded samples and in case of as built parts it was due to dislocation strengthening.