Development and characterization of 316L/Inconel625 functionally graded material fabricated by laser direct metal deposition

Abstract

Functionally graded material (FGM) is a composite with innovative structure and function, which has the good overall performance and meets working requirements in harsh environments. FGM has been widely used in aerospace, biological, nuclear, and photoelectric engineering fields. Laser direct metal deposition (LDMD) is an advanced manufacturing method that is excellent at fabricating objects with optimized geometries and minimizing weight using far less material and energy. In this paper, FGM with the constitution varying from 100% 316L stainless steel to 100% Inconel625 alloy was successfully fabricated using LDMD technology. Grain morphology, composition, mechanical properties and abrasive resistance were obtained to investigate the microstructure and mechanical performance of FGM. With the Inconel625 content increasing, primary dendrite arm spacing gradually increased, and white second phases began to precipitate along dendrites boundary when the content of Inconel625 exceeded 80%. Micro-hardness gradually increased from 216.47 HV at the bottom of FGM to 355.7 HV at the top. With micro-hardness and the hard phase volume increasing, the wear rate of FGM declined and the wear resistance was improved. The fracture element analysis showed that a large number of small and uneven distributed second phases led to the graded material fracture and the tensile fracture mechanism was of typical micro-porous aggregation toughness fracture.