Effect of the Microstructure on the Corrosion and Fatigue Behavior of the Additively Manufactured M789 Stainless Steel

Abstract

Corrosion is one of the most destructive on the environment and also on our safety. Not only does the microstructure influence the severity of corrosion, but also does many other chemical and mechanical factors such as fatigue. For this reason, the ability to evaluate and further predict localized corrosion on materials subjected to stress has been a growing interest in an attempt to foresee the fatigue-corrosion damage before escalating into a material failure, years later.A quantitative and qualitative investigation was conducted to assess the effect of the heterogeneous microstructure on the fatigue and corrosion resistance of the additively manufactured martensitic stainless steel, AMPO M789, employed in application where a high hardness and corrosion resistance is of need. We first examined quantitatively the inclusion content of polished surfaces and the roughness of net-shaped samples, in order to estimate the fatigue strength of the alloy with statistics of extreme values and linear fracture mechanic approach. We then exposed the material to electrochemical tests in synthesized seawater, in order to identify possible corrosion mechanisms and to further assess the pits initiation and their dimensions. Considering those results, we finally predicted a possible performance of M789 in high-cycle fatigue in presence of corrosive environment. We believe our work represents a first step towards studying the synergistic effect of localized corrosion and fatigue strength on the heterogeneity of this new additively manufactured alloy.