Influence of composition gradient variation on the microstructure and mechanical properties of 316 L/Inconel718 functionally graded material fabricated by laser additive manufacturing

Abstract

Abstract Laser metal deposition (LMD) is an advanced manufacturing technology combining rapid prototyping and laser cladding technology, which has been applied to manufacture high performance parts with complex structure. In this study, Inconel-steel functionally graded materials (FGMs) with composition transitioning from 100 % 316 L incrementally graded to 100 % Inconel718 by different composition gradients (5%, 10 %, 20 %) were fabricated by LMD. The microstructure, phase evolution and mechanical properties of the components with different composition gradients (5%, 10 % and 20 %) were characterized by microscopy, energy dispersive spectroscopy, X-ray diffraction, micro-indentation and tensile tests. Brittle Laves phase could be observed when the content of Inconel718 exceeded 40 %. With the composition gradient decreasing, the range of micro-hardness along the deposition direction enlarged. The FGM micro-hardness had the widest range of 173 HV-308 HV when composition gradient was 5%. Fe and Ni, the main elements of alloys used in this study, transitioned linearly along the gradient direction and diffused fully between layers. By linearly fitting Fe content, the effect of composition gradient on element transition was determined. The presence of Laves phase was the main inducement leading to the micro-porous aggregation fracture. The best tensile properties with the highest tensile strength (527.05 MPa) and the highest elongation (26.21 %) were obtained by the FGM with composition gradient of 10 %. The findings will be helpful to choose appropriate gradient variation and understand the forming mechanism of functionally graded materials fabricated by laser additive manufacturing.