Microstructure tailoring of laser powder bed fused 316L impellers for enhanced mechanical properties and optimum electrochemical characteristics through hot isostatic pressing
Yahya Aghayar, Ayda Shahriari, Mojtaba Shakerian, Mackenzie Purdy, Mohsen Mohammadi
Abstract
This study investigates the design, manufacturing, and post-processing of 316L stainless steel impellers fabricated using laser powder bed fusion (LPBF) for optimum mechanical properties and corrosion resistance. The as-built components were fabricated using optimized manufacturing parameters, starting with reduced-dimension prototypes featuring various angles. Tailoring the characteristics of the impellers involved stress relieving, hot isostatic pressing (HIP) at 100 MPa and 1150 °C for 4 h, and machining. To assess the impact of these processes on the component functionality, microstructural, mechanical, and electrochemical (MMEC) characterizations were conducted. The as-built microstructure displayed hierarchical features, including melt pools, micrograins, and sub-grains. Following the HIP process, melt pool boundaries and sub-grain features disappeared, resulting in more equiaxed and finer grains and a reduction in porosity to 99.8 % ± 0.05. Additionally, the formation of annealing twins was observed post-HIP, influencing both mechanical and electrochemical properties. While the ultimate tensile strength decreased after HIP, the elongation to failure improved, and both ultimate tensile and yield strength met the standard requirements for 316L stainless steel. Electrochemical analysis showed similar corrosion behavior for both as-built and HIP components, though resistance to localized corrosion, particularly pitting, slightly decreased after HIP. However, HIP caused the least reduction in localized corrosion resistance when compared to other post-heat-treatment techniques observed in LPBF components. Overall, HIP proved to be an effective heat-treatment process for tailoring physical, mechanical, and electrochemical properties of impellers.