Corrosion Behavior of Additively Manufactured Austenitic Stainless Steel for Nuclear Power Plants

Abstract

This project aims to study the corrosion behavior of additively manufactured (AM) austenitic stainless steel produced using Laser Powder Bed Fusion (L-PBF) method. This material is becoming increasingly popular in various industries, namely the nuclear power plant industry. Metals fabricated using LPBF or any AM method result in a difference in microstructure compared to conventional manufacturing methods, which results in differences in mechanical, physical, and chemical properties. A thorough grasp of metals fabricated using AM corrosion resistance is imperative, given the growing use of additive manufacturing techniques in nuclear power plants to fabricate complex components. The study evaluate the corrosion resistance and some mechanical properties of L-PBF manufactured SS316L utilizing electrochemical methods, surface analysis, and microstructural analyses. Another aim of this study is to observe the influence of processing parameters on the properties of the fabricated LPBF 316L specimen. Observing the porosity using surface analysis has shown that processing parameters play a huge role, specimens fabricated using high laser power and scanning speed and low hatch distance have shown the lowest porosity due to the sufficient melting and fusion between layers. The observed microstructure has shown to be typical of laser technologies showcasing melt tracks and pools due to the scanning laser. An increase in melt pool and track overlaying was observed at lower hatch distance and discontinuous melting was observed in specimens fabricated at low laser power and scanning speed. Electrochemical corrosion tests in three different solutions (0.6M NaCl, 1M HCl, and 1M NaOH) have shown that LPBF 316L specimens can have enhanced corrosion resistance compared to conventional 316L at the correct processing conditions. The presence of porosity plays a role in 0.6M NaCl and 1M NaOH solutions, where lower porosity is favored in achieving greater corrosion resistance properties. However, porosity isn’t the only factor, analysis of the influence of processing parameters has shown that an increase in hatch distances is favorable in achieving greater corrosion resistance properties in 0.6M NaCl solutions, due to the decrease in melt pool boundaries, which tend to contain defects that initiate pitting. However, this trend is less apparent in 1M HCl and 1M NaOH solutions, which indicates other factors playing a role and further testing is required. Electrochemical corrosion tests in hydrogen peroxide-containing environments have shown that increasing hydrogen peroxide concentration promotes passive layer formation, which indicates changes in passive layer properties. Further testing is required to determine the performance of the passive layer formed in such solutions. The results showcase that 316L fabricated using LPBF can have greater corrosion resistance properties at the correct processing conditions, and is a step forward in the implementation of AM metals in various industries including the nuclear sector.

Date of Award	9 Dec 2024
Original language	American English
Supervisor	Akram Alfantazi (Supervisor)