Characterization of Inconel/steel bimetallic structures fabricated by selective laser melting

Abstract

Multi-material combinations in selective laser melting (SLM) have been a challenge to achieve compared to a single material build. The benefits of additive manufacturing (AM) can also be brought to fabrication parts with multiple materials such as pressure tubes of nuclear reactors which uses 316L stainless steel and Inconel 718. Traditionally welding was used to combine them which had negative effects which caused defects that would compromise the structure. In this project, characterization of Inconel/steel bimetallic structure fabrication by SLM was carried out. The objectives were to analyze and compare the samples with varying process parameters and linear energy densities. The characterization techniques used were optical microscopy (OM), scanning electron microscope (SEM) and energy dispersive spectroscopy (EDS). It was found that at the interface, a lower linear energy density (LED) would result in lesser cracks but increased incomplete fusions pores. Increasing LED would result in larger cracks, but it was observed at the highest LED set of parameters (LED = 0.91 J/mm) that large cracks throughout the interface is significantly reduced. The depth of the intermixed region trend was observed that higher LED would result in more diffusion between the two materials which is better. Higher microhardness values readings were taken for parts with fewer large cracks but could not account for the porous nature of the sample. LED = 0.91 sample would go against the trend with comparable microhardness values due to lesser large cracks.