Environmental Degradation of Additively Manufactured Alloys: AM Materials and Aqueous Corrosion - Part II: Stainless Steel, Inconel 718 and Coatings
Sponsored by: TMS Structural Materials Division, TMS: Corrosion and Environmental Effects Committee, TMS: Additive Manufacturing Committee
Program Organizers: Kinga Unocic, Oak Ridge National Laboratory; Jenifer Locke, Ohio State University; Sebastien Dryepondt, Oak Ridge National Laboratory; Michael Kirka, Oak Ridge National Laboratory; Xiaoyuan Lou, Purdue University; Brendy Rincon Troconis, University of Texas at San Antonio; Luke Brewer, University of Alabama
Thursday 8:30 AM
March 18, 2021
Room: RM 20
Location: TMS2021 Virtual
Session Chair: Brendy Rincon Troconis, University of Texas at San Antonio; Luke Brewer, University of Alabama
8:30 AM
Localized Corrosion of Additively Manufactured Stainless Steels: Michael Melia1; Jesse Duran1; Rebecca Marshall2; Ryan Katona2; Rebecca Schaller1; Jeffrey Rodelas1; Michael Heiden1; Bradley Jared1; Robert Kelly2; Eric Schindelholz3; 1Sandia National Laboratories; 2University of Virginia; 3The Ohio State University
Additively manufactured (AM) metals exhibit numerous microstructural and morphological differences compared to their wrought counterparts from dislocation cell structures to uniquely rough surfaces. The influence these unique features have on the metals’ corrosion resistance are still under investigation with most current works limited to laboratory experiments. The current state of understanding for AM stainless steels in corrosive environments will be presented along with active research including: the atmospheric corrosion behavior of AM stainless steels, reasons for localized corrosion attack of melt pool boundaries, and the impact as-printed roughness has on the local corrosion of AM metals. Several aspects of how the surface roughness of an AM part controls local corrosion will be explored including surface finishing treatments for mitigation and a COMSOL approach to predict pit stability.SNL is managed and operated by NTESS under DOE NNSA contract DE-NA0003525. SAND2020-6651 A.
8:50 AM Invited
Melt Pool Boundaries and the Corrosion of Laser Powder Fusion Stainless Steels: Eric Schindelholz1; Michael Melia2; Christopher Barr3; Bradley Jared3; Jeffrey rodelas3; Paul Kotula3; 1Ohio State University; 2Sandia National Laboratories ; 3Sandia National Laboratories
The nature of melt pool boundaries (MPBs) in additively manufactured alloys are characteristically delineated by differences in grain or subgrain orientation, size and morphology. They may also possess more subtle attributes, such as enrichment of secondary phases or non-uniform residual stresses, which have yet to be fully realized. Several groups have recently reported that MBPs in selective laser melted (SLM) stainless steels suffer considerable localized attack under certain oxidizing and acidic conditions. This behavior has been attributed to secondary phases, pores or non-uniformities in residual stress at the MPB, but without definitive evidence. Here we present electrochemical and detailed electron microscopy results that evidence the characteristics and origin of MPB susceptibility in SLM austenitic stainless steels. The implications of these results along with mitigation strategies, including heat treatment, will also be addressed.SNL is managed and operated by NTESS under DOE NNSA contract DE-NA0003525. SAND2020-7397 A.
9:20 AM Invited
Selective Corrosion and Sensitization Behavior in Laser Powder Bed Fusion 316L: Robert Kelly1; Duane Macatangay1; Jenna Conrades1; Keegan Brunner1; 1University of Virginia
Application of the laser powder bed fusion (LPBF) process to stainless steel alloys, such as 316L, present promise due to the excellent strength and corrosion resistance of the wrought counterpart. Despite growing interest in the research and application of LPBF, little work has been performed to characterize the behavior of these alloys in aqueous environments. As with conventional welding processes, the non-equilibrium structure arising from rapid solidification presents potential issues in selective corrosion in these alloys. This work applies metallographic methods and electrochemical testing to determine the susceptibility of these alloys to selective attack at microstructural features such as melt pool boundaries. Susceptibility of sensitization is also investigated to assess the resistance of these alloys to intergranular corrosion from post-process heat treatments. Findings include melt-pool boundary attack and susceptibility to rapid sensitization that is not observed in conventionally wrought 316L.
9:50 AM
High Performance AM Stainless Steel 316L Under Corrosive Environment: Thomas Voisin1; Zhen Qi1; Yuliang Zhang1; Rongpei Shi1; Josh Kacher2; Manyalibo Matthews1; Brandon Wood1; Y. Morris Wang1; 1Lawrence Livermore National Laboratory; 2Georgia Tech
In this work, we investigate the performance of additively manufactured 316L stainless steel (AM316L SS) in corrosive solution (NaCl). Our main results show that the rapid solidification-induced chemical heterogeneities and the process-induced high surface roughness do not prevent the as-built material to far exceed the corrosion pitting potential of the conventional 316L SS. The first part of the talk will introduce the multi-scale microstructural features that are present in the as-built and annealed AM 316L SS. The second part will focus on understanding why the AM 316L SS is better than its conventional counterpart. To ensure a multi-scale experimental and theoretical approach, we use state-of-the-art in and ex situ electron microscopy, galvanic corrosion testing, and atom force microscopy in addition to phase-field simulations.This work was performed under the auspices of the U.S. Department of Energy by Lawrence Livermore National Laboratory under Contract DE-AC52-07NA27344.
10:10 AM
Improving the Corrosion Performance of Additively Manufactured 316L via Chemically-modified Feedstock: Joseph Sopcisak1; Steven Storck1; Rengaswamy Srinivasan1; Jason Trelewicz2; David Sprouster2; Kevin Hemker3; Mo-Rigen He3; Timothy Montalbano1; 1Johns Hopkins University Applied Physics Laboratory; 2Stony Brook University; 3Johns Hopkins University
Due to the complex thermal profiles associated with consolidation of material on small length scales, additive manufacturing (AM) has many advantages over conventional manufacturing methods. Nevertheless, the implementation of AM into corrosive environments is ultimately limited by the poor corrosion performance of metal AM components when compared to their conventionally manufactured counterparts. We demonstrate improvement in the pitting corrosion resistance of AM-316L via modification of the feedstock material. In this effort, 316L powder was modified by adding trace amounts of ceramic dopant. Test specimens were manufactured in a LPBF system and were consolidated via SLM. The resultant material shows little or no evidence of pitting corrosion in aqueous solutions of 5%, 30% and 60% FeCl3. It also remains free of pitting corrosion under anodic polarization in aqueous 3.5% sodium chloride electrolyte. High resolution TEM and synchrotron x-ray analysis were carried out to understand the underlying mechanisms causing this improvement.
10:30 AM
Electrochemical Response of Additively Printed Inconel 718 by Laser-based Direct Energy Deposition: Sangram Mazumder1; Mangesh V. Pantawane1; Yee-Hsien Ho1; Narendra B. Dahotre1; 1University of North Texas
Precipitation hardened nickel-based superalloys marks a long tradition of applicability in oil field applications owing to their superior resistance to extreme environments. Additive manufacturing with all its fabrication advantages is breaking into oil and gas industries, promising rapid fabrication and repair of critical components. This research aims to investigate and underline the electrochemical behavioral traits of additively printed nickel superalloy Inconel 718 using laser-based direct energy deposition, known as DED. Electrochemical behavior was assessed using potentiodynamic polarization techniques and electrochemical impedance spectroscopy, and microstructural features were observed using scanning electron microscopy. Isotropic electrochemical behavior was observed in the horizontal and vertical sections of the DED printed Inconel 718 part with rapid detachment of undissolved secondary phases leading to higher current efficiencies at low current densities. Electrochemical behavioral results indicated similar and comparable traits in terms of pitting, in additively printed and commercially available Inconel 718.
10:50 AM
Corrosion Behavior of Functionally Graded Inconel 718 Produced by Additive Manufacturing: Yaiza Gonzalez-Garcia1; Lola Devignes2; Aytac Yilmaz1; Arjan de Groot1; Evgenii Borisov3; Vera Popovich1; 1Delft University of Technology; 2SIGMA Clermont; 3Peter de Great Saint-Petersburg Polytechni University
The corrosion behavior of functionally-graded (FGM) Inconel 718 manufactured by Selective Laser melting (SLM) was studied. A set of different process parameters was used to print specimens featuring a columnar coarse-grained (~500µm) and a fine equiaxed-grained (~100µm) structure with interface region of ~10µm. The corrosion properties were evaluated by polarization, EIS, SKP and SECM localized measurements in a 3.5%-NaCl solution on different with respect to building direction surfaces. Results showed no significant differences in the overall corrosion performance of the different zones, with the presence of a passivity region and high-capacitive response in the EIS spectra. The as-processed graded SLM specimens showed a comparable behavior to a commercial wrought and heat-treated Inconel alloy. From SKP and SECM, local differences in the reactivity of the zones were elucidated and directly correlated to the microstructural differences. The graded interface showed a gradual transition between the regions, without a dramatical change in reactivity.
11:10 AM
Nano-crystalline Cold Spray Coatings for Repair and Retrofit of Existing Large-Scale Structures: Rose Gerani1; Baillie Haddad1; Kris Klus1; Christian Widener1; 1VRC Metal Systems
Cold spray processing is a solid-state, additive manufacturing method of developing coatings with fine microstructures, high tensile strength and adhesion, superior wear performance, and tailorable anodic or cathodic corrosion protection. In structural applications, steel is often exposed to aggressive atmospheric conditions, which frequently occurs in highly polluted areas or near saltwater, causing much higher corrosion rates than experienced in rural environments. Nevertheless, damage to critical structural members over time is unavoidable, due to any number of anticipated or unanticipated loading and environmental conditions. Conventional modes of repair, such as welding, often introduce additional problems, such as cracking caused by high tensile residual stresses at inherent discontinuities in the weld, corrosion sensitized areas adjacent to the weld repair, and weakening of the surrounding material from the heat input. In this novel work, a nano-crystalline cold spray coating was optimized for corrosion and wear protection of structural steel, using nitrogen.
11:30 AM Invited
Tailoring Microstructure in Additively Manufactured Stainless Steels for Enhanced Corrosion Performance: Jason Trelewicz1; David Sprouster1; Gary Halada1; Joseph Sopcisak2; Steven Storck2; 1Stony Brook University; 2The Johns Hopkins University Applied Physics Laboratory
In laser additively manufactured 316L, enhanced pitting susceptibility has been discussed in the context of the cellular microstructure that forms during printing. Interestingly, some studies also report on laser printed samples with seemingly enhanced stability against pitting relative to wrought 316L. The complexity of these highly heterogeneous microstructures has thus made it difficult to identify the mechanisms governing localized attack, and in turn design printed alloys with performance exceeding their wrought counterparts. In this study, we explore the microstructural underpinnings of localized corrosion in laser additively manufactured 316L using multi-modal characterization techniques. The dislocation density and its dependence on printing conditions are correlated to chemical heterogeneities formed at the nanoscale. On this basis, accelerated pitting is attributed to depletion of Cr and carbide formation in regions of high dislocation density. We finally show that ceramic dopants can inhibit accelerated pitting corrosion by augmenting the chemical state of the cellular walls.