A scientific framework to adopt additively manufactured 316L stainless steel closed faced impellers in the power generation sector: Microstructural control, mechanical properties, and fatigue performance

Abstract

Closed-face impellers are critical rotating components widely used in energy, marine, and aerospace industries, where their complex geometries and demanding fatigue performance requirements make a reliable competition for conventional manufacturing. Laser Powder Bed Fusion (LPBF) offers a promising alternative for producing such components; however, the reliable adoption of LPBF parts in safety-critical applications requires a deeper understanding of the relationships between processing conditions, defects, microstructure, and mechanical performance. This thesis establishes a scientific framework for the qualification of LPBF-316L stainless steel components by integrating process optimization, microstructural characterization, and mechanical performance evaluation. Laboratory-scale specimens were first fabricated to investigate the influence of LPBF process parameters and internal defects on microstructure and mechanical behavior. Hot Isostatic Pressing (HIP) was subsequently applied as a post-processing strategy to reduce porosity, homogenize the microstructure, and improve material integrity. Comprehensive characterization, including microstructural analysis, uniaxial tensile testing, corrosion assessment, and rotating bending fatigue testing, was conducted on both as-built and HIP materials. The results demonstrated that HIP significantly enhances the structural integrity and fatigue performance of LPBF-316L. Near-full densification was achieved, ductility increased by approximately 80%, and fatigue endurance improved by about 50 MPa in the high-cycle fatigue regime (10⁶–10⁷ cycles) at 450 °C compared to as-built samples. In addition, the role of defects and corrosion-induced pitting in fatigue crack initiation and propagation was identified. The framework developed in this study was further validated through the successful fabrication of a full-scale LPBF-316L closed-face impeller, demonstrating the feasibility of transitioning additively manufactured stainless steel components from laboratory investigations to industrial applications.