Effects of Heat Treatment on Microstructure Change and Mechanical Performance of Additively Manufactured 316L Stainless Steel Stents

Abstract

Currently, percutaneous coronary intervention, based on stenting, is employed to provide scaffolding support to correct occlusion and diminished blood supply caused by atherosclerosis. To guarantee procedural efficacy and enhanced structural integrity of stents, further developments of stent materials and manufacturing methods are particularly required. In this paper, 316L stainless steel stents fabricated by additive manufacturing are studied through heat treatment, microstructural characterization, and mechanical deformation in vitro. After solution heat treatment conducted at 1200°C for durations ranging from 1 to 4 h, coarsening of columnar grains and changes in the grain boundary characters were observed, indicating the potential of microstructure modification through heat treatment. Electrochemical polishing can effectively improve surface quality by dissolving surface imperfections caused by partially sintered powders and uneven solidification processes, characteristics of additively manufactured parts. Mechanical deformation behaviors are evaluated by expansion tests before and after heat treatment. Specifically, free expansion tests are carried out to assess the mechanical performance of the stent alone, while in vitro mechanical performances are evaluated using silicone arteries filled with silicone plaques, corresponding to a stenosis rate of 70%. Coarsened grain microstructures in heat-treated stents lead to improved expansion flexibility, reduced dog-boning ratio, and slightly increased recoil, as compared to the as-printed stents. Results demonstrate the viability of improving the mechanical performance of additively manufactured 316L stainless steel stents through heat treatment process.