Nanometer-scale porosity evolution and mechanical properties of additively manufactured 17-4PH stainless steel.

Understanding of the microstructure and mechanical properties of additively manufactured (AM) 17-4PH stainless steel has matured significantly, but combined wrought-level strength and ductility has yet to be achieved. Identifying the microstructural obstacle(s) impeding this milestone is critical for many future applications and industries interested in this AM alloy. In this work, microstructure, mechanical properties, and fracture behavior is evaluated for AM 17-4PH built via the laser powder bed fusion technique (LPBF) and heat treated via a broad range of techniques to achieve wrought-level 17-4PH strength. The highest strength/ductility was achieved with a two-stage hot isostatic press (HIP) and solution anneal (SA) treatment followed by an aging heat treatment, but wrought-level ductility could not be matched. Persistent nano-porosity (0.06–0.23 μm) was identified and correlated to fracture surface dimpling (R2 = 0.73–0.85) indicating a possible role in this ductility limitation. Contextualization of this study's mechanical properties dataset within the literature suggests that this observation is endemic to the current state-of-the-art processing techniques for AM 17-4PH. • HIP minimizes larger pores, but nanometer-scale pores (60 nm) persist and coarsen. • Reviews 40+ AM 17-4PH mechanical properties studies grouped by heat treatment. • Apply a SA+460 °C/1 h treatment for balanced strength, ductility, and cost. • Apply HIP + SA+460 °C/1 h for strength/ductility and wrought-like microstructure. [ABSTRACT FROM AUTHOR]