Effects of transition layer thickness on microstructure and mechanical properties of STS 316L/In718 functionally graded material fabricated by LMD

Purpose Laser metal deposition is an ideal method to fabricate functionally graded materials (FGMs) whose properties vary with the dimensions, and the transition layer would highly influence the mechanical properties. However, the transition layer thickness is mostly an arbitrary set. This study aims to investigate the influences of the deposited layers number of FGMs on the microstructure, phase, composition and mechanical properties of FGMs. Design/methodology/approach To investigate the effect of thickness of transition layer on the microstructure and mechanical properties of STS 316 L/Inconel 718 FGMs, the number of individual compositional layers was designed to be 10, 20 or 30 for each composition, and the microstructure, composition and mechanical properties were compared among the deposited samples. Findings As the number of deposited layers increased, the primary dendritic arm spacing increased due to more heat accumulation, the Laves phase was dissolved, the lattice constant increased, the compositional transitions changed from continuous linear to discontinuous gradient transitions. In bad performance addition, the range of microhardness increased and the tensile properties decreased due to the formation of hot cracks. The tensile properties of the FGM components depended on the combined effect of the improvement due to the dissolution of the Laves phase and the degradation due to the formation of hot cracks. The highest tensile strength for 522.77 MPa and the highest elongation for 18.77% were obtained by the component with the least deposited layers. Originality/value The effects of layer thickness on the microstructure and mechanical properties of STS 316 L/Inconel 718 FGMs were investigated to provide a layer thickness reference for the fabrication of FGMs. This study provides an understanding of the correlation between the thickness of the transition layer and microstructure, dendrite spacing, hardness and tensile properties of FGMs.