Environmental Degradation of Additively Manufactured Alloys: Environmentally Assisted Cracking (Hydrogen Embrittlement and SCC) / Bio-Corrosion
Sponsored by: TMS Structural Materials Division, TMS: Corrosion and Environmental Effects Committee
Program Organizers: Kinga Unocic, Oak Ridge National Laboratory; Jenifer Locke, Ohio State University; Sebastien Dryepondt, Oak Ridge National Laboratory; Brendy Rincon Troconis, University of Texas at San Antonio; Andrew Hoffman, Catalyst Science Solutions; Xiaoyuan Lou, Purdue University

Tuesday 2:30 PM
March 21, 2023
Room: Sapphire 400A
Location: Hilton

Session Chair: Andrew Hoffman, GE Research, US; Kinga Unocic, ORNL; Sebastien Dryepondt, ORNL


2:30 PM  
Combining NanoSIMS and EBSD Analysis to Define Hydrogen Trapping in Additively-manufactured Stainless Steel 316L: Kaila Bertsch1; P.K. Weber1; Shohini Sen-Britain1; Thomas Voisin1; Chris San Marchi2; Brandon Wood1; 1Lawrence Livermore National Laboratory; 2Sandia National Laboratories
    The diffusion of hydrogen through metallic materials has been studied for decades due to its influence on hydrogen embrittlement, however, hydrogen trapping at specific microstructural features remains incompletely understood. Additive manufacturing (AM) of metals creates distinctive dislocation and segregation structures that offer a unique opportunity to deconvolute the effects of features such as dislocation structures, precipitates, and grain boundaries. In this study, hydrogen trapping was probed directly by combining SEM and EBSD of crystallographic structures and defects with high-resolution NanoSIMS to define hydrogen distributions in stainless steel 316L. Trapping was compared in deuterium gas-precharged components in the AM as-fabricated state, in the well-annealed state, after intermediate straining, and after failure to compare hydrogen redistribution with the evolution of deformation. These observations enabled a novel, direct comparison of the influence of dislocations, grain boundaries, and precipitates on critical aspects of hydrogen transport and trapping.

2:50 PM  
Stress Corrosion Cracking Growth in Additively Manufactured 316L Stainless Steel: Ainsley Pinkowitz1; Tressa White1; 1Naval Nuclear Laboratory
    Additively manufactured (AM) metals have opened exciting pathways for versatility and agility. For components which require stress corrosion cracking (SCC) resistance, AM replacements will need to display equal or slower SCC growth rates to the traditional wrought equivalent. Testing was performed in this work to observe the susceptibility of AM 316L stainless steel (SS) to SCC in both deaerated pure water and aerated, ion faulted conditions at temperatures of 177 – 360°C. Effects of orientation, temperature, environment, and different processing conditions will be discussed. Results indicate superior SCC resistance in the AM 316L compared with its wrought counterpart. A clear orientation dependence was observed, with X-Z (i.e. Crack growth in the direction of dendritic grain growth) having the highest growth rates. Overall AM 316L SS makes a very promising material for use where typical 304/304L or 316/316L wrought is already employed with regards to its impressive SCC growth resistance.

3:10 PM  
Evaluation of Hydrogen Diffusivity, Uptake, and Trapping in Additively Manufactured 17-4 PH Stainless Steel and Possible Consequences Towards Stress Corrosion Cracking: Lauren Singer1; Zachary Harris1; John Scully1; 1University of Virginia
    Hydrogen-metal interactions, such as production, uptake, diffusion, and trapping, can greatly influence the degree of stress corrosion cracking of a material; therefore, evaluation of H interactions in additively manufactured stainless steels is critical in corrosion performance and failure analysis. This work aims to quantify bulk hydrogen behavior of selectively laser melted 17-4 PH stainless steels compared to their wrought counterparts. Electrochemical permeation was used to assess effective hydrogen diffusivity and hydrogen concentration for each condition; the impact of surface effects was examined through specimen thickness variation. Microstructural trapping was investigated through thermal desorption spectroscopy. The barnacle electrode technique and LECO hydrogen testing were used to evaluate diffusible H concentration and total hydrogen uptake, respectively. Results indicate a four- to fivefold increase in global effective diffusivity in additively manufactured versus wrought material, with the usual relationship between temper and hydrogen interactions preserved; possible impacts on stress corrosion cracking are addressed.

3:30 PM  
Hydrogen Embrittlement of Cathodically Pre-charged Inconel 718 Fabricated via Selective Laser Melting: Claudia Santos Maldonado1; Alfredo Zafra1; Emilio Martinez-Pañeda1; Roberto Morana1; Minh-Son Pham1; 1Imperial College
    Additively manufactured (AM) Inconel 718 holds great potential in aerospace, power generation and oil & gas applications due to its excellent mechanical properties. However, to ensure the mechanical integrity and assist the development of next generations sustainable 3D printed Ni-based alloys, this phenomenon needs to be thoroughly studied and understood. In this work, the hydrogen embrittlement (HE) susceptibility of AM Inconel 718 is investigated via pre-cathodic charging in 3wt.% NaCl at 90°C. SEM and EBSD results show the difference in grain morphology, SSRT shows the transition from ductile to brittle with a reduction of ductility to 11% and 5%, in wrought and AM, respectively. And post-mortem fractography analysis brings insights into the HE mechanisms driving the failure process; mainly, microvoid formation (MVC), localized plasticity (HELP) and decohesion of lattice (HEDE) that leads to intergranular cracking along the equiaxed grains in wrought or through cell dendrites in AM specimens.

3:50 PM  
The Effect of Hydrogen Embrittlement on Additively Manufactured IN718 in Dependency of the Delta Phase Volume Fraction: Andreas Kirchmayer1; Jan-Oliver Hücking1; Felfer Peter1; Mathias Göken1; Steffen Neumeier1; 1Friedrich-Alexander Universität Erlangen-Nürnberg
    To realize the change in mobility needed to achieve the environmental goals set by governments all around the world, new means of resource-saving production as well as a new energy carrier is needed. Additive manufacturing and hydrogen as fuel in jet engines can contribute to solve both these problems for the aerospace sector. This work aims to analyze the influence of hydrogen embrittlement on the Ni-based superalloy IN718 manufactured by selective laser melting (SLM) using electrochemical hydrogen charging and subsequent tensile tests. By applying different heat treatments, the morphology as well as the amount of the high temperature delta phase can be changed. It is shown, that an increase in delta volume fraction leads to stronger hydrogen damage, as one of the main reasons for hydrogen embrittlement is the delamination around delta precipitates. To validate any effect stemming from the SLM process, the results are compared to conventional forged IN718.

4:10 PM Break

4:30 PM  
Biocorrosion Response of Heterogeneous Microstructure in Laser Additively Deposited CoCrMo: Sangram Mazumder1; Selvamurugan Palaniappan1; Mangesh V. Pantawane1; Madhavan Radhakrishnan1; Shreyash M. Patil1; Narendra Dahotre1; 1University of North Texas
    Bio-corrosion response of laser-based directed energy deposited CoCrMo in simulated body fluid at physiological temperature (37 ℃) was investigated. The cellular-dendritic solidification with selective elemental segregation in CoCrMo fabricated using five different laser powers. Such microstructural evolution was attributed to the extremely rapid thermokinetics inherently associated with laser-based additive manufacturing. Bio-corrosion response in terms of potentiodynamic polarization and electro-impedance spectroscopy of the laser additively manufactured CoCrMo samples varied marginally, compared to a conventionally manufactured CoCrMo. However, significant difference in corrosion morphology characterized by spatially non-uniform corrosion was observed in laser additively manufactured CoCrMo, while a homogeneous corrosion was observed in conventionally manufactured CoCrMo. Heat treatment at 1150 ℃ for 150 minutes in Ar atmosphere eliminated the microstructural heterogeneity in laser additively manufactured CoCrMo samples rendering uniform corrosion characteristics. Also, enhancement in equilibrium potential was observed, attributed to the specific microstructural aspects after heat treatment of the laser additively manufactured CoCrMo.

4:50 PM  
Biocorrosion Response of Laser Additively Deposited TiNbSn Alloy in Physiological Medium: Selvamurugan Palaniappan1; Sangram Mazumder1; Madhavan Radhakrishnan1; Alberto Canales-Cantu1; Narendra B. . Dahotre1; 1University of North Texas
    TiNbSn alloys have been used in biomedical applications for more than decades due to their excellent corrosion resistance, biocompatibility, and high mechanical strength with low Young’s Modulus. Although these alloys are in use for a long time, not many studies have been done using Additive manufacturing to check the material properties to fit certain bio-medical applications. In light of this, an attempt was made to deposit TiNbSn with variable quantities of Nb using laser-based directed energy deposition. The mass percentages of Nb in TiNbSn were varied from 30 wt.% to 35 wt.% and the additively manufactured samples were characterized for microstructures and phases. Biocorrosion response in terms of potentiodynamic polarization and electrochemical impedance spectroscopy of these samples were evaluated in simulated body fluid at physiological temperature (37 ℃) and were compared to that of the cast alloys. Moreover, these results were further related to the microstructural aspects evolved in the additively manufactured TiNbSn.

5:10 PM  
Microstructure and Electrochemical Response of Selective Laser Melted NiTi: Anurag Srivastava1; Chaudhry Usman2; Bilal Mansoor2; Chen Zhang1; Ibrahim Karaman1; Alaa Elwany1; 1Texas A&M University; 2Texas A&M University at Qatar
    This research fabricated the NiTi alloy cubes with SLM and explored the influence of laser power and hatch spacing on its microstructure and electrochemical response. Specimens were fabricated with different laser power, scan speed (80 W/330 mm.s-1, 200 W/1080 mm.s-1) and hatch spacing (64 µm, 80 µm). Electrochemical analyses, in Hanks’ Balanced Salt Solution at 37⁰C, were carried out on surfaces that were parallel and perpendicular to the building direction and were correlated to the microstructure. Microstructures of the specimens were investigated through optical microscopy and SEM. Our initial results indicate that the transverse surface presented columnar grains while the longitudinal surface showed chessboard-like grains. Electrochemical properties determined using electrochemical impedance spectroscopy and potentiodynamic polarization showed that samples fabricated with higher laser power, scan speed and lower hatch spacing had better corrosion properties. Pitting corrosion was observed with pits initiating from porosity defects present in the samples.