Additive Manufacturing Fatigue and Fracture: Developing Predictive Capabilities: Environmental and Corrosion Effects
Sponsored by: TMS Structural Materials Division, TMS: Additive Manufacturing Committee, TMS: Mechanical Behavior of Materials Committee
Program Organizers: Nik Hrabe, National Institute of Standards and Technology; John Lewandowski, Case Western Reserve University; Nima Shamsaei, Auburn University; Mohsen Seifi, ASTM International/Case Western Reserve University; Steve Daniewicz, University of Alabama

Thursday 2:00 PM
March 3, 2022
Room: 258B
Location: Anaheim Convention Center

Session Chair: Mohsen Seifi, ASTM International/Case Western Reserve University

2:00 PM  Invited
Environmental Cracking Behavior of Additively Manufactured 17-4PH Stainless Steel: James Burns1; Trevor Shoemaker1; 1University of Virginia
    Additively manufactured materials intended for use in fracture critical applications must be vetted for environmentally affected crack growth resistance. The current study utilizes fracture mechanics testing to quantify the stress corrosion cracking (da/dt versus stress intensity) behavior of traditionally manufactured 17-4PH stainless steels and its additively manufactured equivalent. The AM samples were subjected to various post-processing steps (HIP and thermal treatments to achieve hardened conditions) to test the AM materials in conditions that would enable direct replacement of traditional components. Testing is performed in full immersion chloride solutions at a variety of electrochemical potentials for 17-4PH. Initial results indicate an enhanced susceptibility for AM materials in both the H900 and H1000 conditions, with AM exhibiting a change in damage mode at modestly severe conditions. The data are interpreted in the context of a micro-mechanical hydrogen embrittlement damage model where microstructural variations are identified and linked to the relevant model parameter.

2:30 PM  
Machining vs Heat Treatment in Additive Manufacturing of Ti6Al4V Alloy: Alireza Dareh Baghi1; Shahrooz Nafisi1; Reza Hashemi2; Heike Ebendorff-Heidepriem1; Reza Ghomashchi1; 1The University of Adelaide; 2Flinders University
    Anisotropy in the mechanical properties of Laser Powder Bed Fusion (L-PBF)-fabricated titanium parts which could be problematic in service, is dependent on the build directions, and may be mitigated by post fabrication treatments such as surface machining or heat treatment. However, investigation of the anisotropy in truly as-printed conditions, i.e., prior to any post process, is always a challenge as the horizontally built parts are noticeably distorted compared to vertically built ones. In this study, by deploying a novel design, straight horizontal samples in the as-printed condition were fabricated. This allowed a comparison to be made possible in the mechanical properties of two built orientations of vertical and horizontal in the as-printed condition. This paper discusses how the surface machining or post thermal treatment influences the anisotropy in the mechanical properties compared to as-printed conditions. It further highlights how annealing process at a temperature of 850C is more effective than stress relieving at a temperature of 670C to nearly diminish the anisotropy in mechanical properties even without any need for machining. Therefore, when machining becomes less feasible due to the geometrical complexity of L-PBF parts, a thermal treatment may be the solution for better service performance.

2:50 PM  
The Elevated Temperature Creep, Fatigue and Fracture Behavior of Additively Manufactured Inconel 718: Michael Kassner1; Theophil Oros1; Kee-Ahn Lee2; Thien Phan3; Lyle Levine3; Andrea Hodge1; 1University of Southern California; 2Inha Univ.; 3NIST
    Elevated temperature creep and fatigue experiments were performed on wrought and additively manufactured (AM) Inconel 718. The creep behavior of the AM Inconel was equal or superior than that of the wrought alloy. However, the elevated-temperature fatigue strength of the AM 718 alloy was inferior to the wrought alloy. More noticeably, the high temperature ductility was dramatically lower than the conventional 718. The basis for the dramatic loss in ductility will be discussed.

3:10 PM  
On Fatigue Performance of Al-Cu-Mg-Ag-Ti-B Alloy: Additive Manufactured Versus Cast: Maryam Avateffazeli1; Md Faysal Khan2; Shuai Shao2; Nima Shamsaei2; Meysam Haghshenas1; 1University of Toledo; 2Auburn University
    In this research, the fatigue behavior of a newly developed laser beam powder bed fusion (LB-PBF) fabricated Al-Cu-Mg-Ag-Ti-B alloy, i.e., A205 alloy, was investigated and compared against the cast counter material in the stress relieved and aged conditions (T7 temper). To correlate the fatigue performance and the microstructural features of the studied materials, electron backscattered diffraction, transmission, and scanning electron microscopy measures were also conducted. The in-situ addition of thermally stable nanosized TiB2 particles along with the very high cooling rate produced through the LB-PBF process resulted in an ultrafine, equiaxed, and uniform grain structure of the additive manufactured material (as compared with the cast counter material) leading to superior mechanical properties. The T7 aged thermal treated materials showed superior fatigue performance as compared with the as fabricated and stress relieved samples. Finally, tangible differences were observed between cast and LB-PBF A205 materials in terms of fatigue performance.

3:30 PM Break

3:50 PM  Invited
Accelerated Corrosion Behavior of Cold Spray Deposited AA2024 and AA7075 and Implications for Mechanical Performance: Gregory Kubacki1; Ozymandias Agar1; Munsu Kim1; Sheri Stanke2; Christine Sanders2; Rachel Black3; Sean Kane3; Luke Brewer1; 1The University of Alabama; 2Naval Research Laboratory; 3Naval Air Systems Command
    This presentation will focus on the environmental performance of cold-gas dynamic spray (cold spray) deposited aerospace aluminum alloys in simulated repair geometries. Cold spray is a promising solid-state technology for additively manufactured repairs to a range of material systems. We will cover the results of laboratory and outdoor, accelerated exposure testing that compares the atmospheric corrosion behavior of cold spray deposited AA2024 and AA7075 to their wrought counterparts. Testing to this point has shown that atmospheric corrosion behavior depends on spray quality and defect density, with idealized, robotically deposited flat-on-plate samples performing equivalently to the substrate, wrought, material. Defects in simulated repair depositions performed by hand resulted in poor conversion coating efficiency at those points, resulting in accelerated localized attack that may serve as crack initiators. Additional testing to investigate corrosion progression at the deposit-substrate boundary and its effect on mechanical stability of the repair will also be presented.

4:20 PM  
Short-crack Growth Behavior in Additively Manufactured AlSi10Mg: Robert Rhein1; Qianying Shi2; J Wayne Jones2; Srinivasan Arjun Tekalur1; Jason Carroll1; Kathleen Chou1; 1Eaton Corporation; 2University of Michigan
    The very high cycle fatigue behavior of an additively manufactured aluminum alloy, AlSi10Mg-T6, has been studied to better understand the role of process related defects on fatigue life and initiation. Ultrasonic fatigue methodologies were used for the determination of an operative fatigue strength. Fatigue crack growth rates were determined for small fatigue cracks that initiated and grew from artificial (FIB) surface defects in specimens subjected to ultrasonic fatigue. X-ray computed tomography (CT) was used in an effort to detect possible crack initiation and growth in specimens cycled for fractions of the nominal VHCF fatigue strength. Small crack growth from FIB-produced micronotches appeared to be transgranular and noncrystallographic. While modest increase in size of some features identified by x-ray CT for interrupted fatigue tests was observed, particularly at defects characterized as flat or oblate spheroids, no definitive evidence of the emergence of a fatal crack from a single defect was found.

4:40 PM  
High Cycle Fatigue Behaviour of Additively Manufactured 316L Austenitic Stainless Steel: Punit Kumar1; Jayaraj Radhakrishnan1; James McKinnell2; Upadrasta Ramamurty1; 1NTU Singapore; 2HP Inc.
    The microstructures, and mechanical properties of the 316L SS fabricated using binder jet printing (BJP) and laser powder bed fusion (LPBF) were investigated and compared with those of the conventionally manufactured (CM) alloy, with particular emphasis on the high cycle fatigue resistance. Results show that the work hardening behavior, ductility, and fatigue strength (σf) of the BJP specimens, which contain significant amounts of pores, are surprisingly comparable to those of the CM alloy. In contrast, the SLM specimens are considerably stronger, less ductile, and far inferior in terms of σf although the porosity in them is relatively smaller as compared to the BJP specimens. Because of the deformation behaviour and combination of other microstructural factors the small cracks that nucleate at the corners of the pores were arrested, both under quasi-static and cyclic loads; therefore, neither ductility nor σf of the BJP alloys were adversely affected by the porosity.