Additive Manufacturing Fatigue and Fracture IV: Toward Confident Use in Critical Applications: Processing-Structure-Property-Performance II
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; Steve Daniewicz, University of Alabama; Nima Shamsaei, Auburn University; John Lewandowski, Case Western Reserve University; Mohsen Seifi, ASTM International/Case Western Reserve University

Tuesday 8:30 AM
February 25, 2020
Room: 10
Location: San Diego Convention Ctr

Session Chair: John Lewandowski, Case Western Reserve University


8:30 AM  Invited
Tailoring the Microstructures of AM Metals for Enhanced Fracture Toughness and Fatigue Resistance: Ramamurty Upadrasta1; 1NTU
    Additive manufacturing of metallic components offers a number of exciting opportunities, which includes the possibility of exploiting the micro- and meso-structural features for enhancing strength-toughness-fatigue resistance combinations. In this presentation, I shall review some of our recent work on SLM Ti-6Al-4V, with particular emphasis on understanding their quasi-static tensile, fracture, fatigue crack growth, and unnotched fatigue properties, both in the as-SLM state as well as after post-SLM heat treatments.

9:00 AM  
High Strain Rate Fracture Properties of Additively Manufactured (AM) Stainless Steel: Kevin Lamb1; Josh Kacher2; Katie Koube2; 1University of Tennessee-Knoxville; 2Georgia Institute of Technology
     The majority of mechanical property testing for AM samples has been dedicated to static or quasi-static loading conditions. Typically, those properties represent commonly accepted attributes used by design engineers. In reality, the mechanical properties of materials under rapid loading conditions often differ greatly from the static case.Gas gun uniaxial strain plate-impact experiments were performed to determine high strain rate compression and tensile (spall) strength and fracture behavior of additively manufactured 316L SS samples at flyer plate velocities up to 1000 m/s (producing strain rates up to 10^5 s-1). The dynamic strength based on free-surface velocity measurements using VISAR and PDV interferometry, combined with in-depth characterization of the fracture morphology on soft-recovered impacted samples using electron microscopy will be presented. Correlation of the strength and fracture behavior with respect to voids within AM steels coupled with NDE of the samples to enable process-structure-property mapping will be discussed.

9:20 AM  
Surface Roughness and Layer Orientation Effects on Fatigue Behavior of LB-PBF Inconel 718 in the High Cycle and Very High Cycle Fatigue Regimes: Palmer Frye1; Muztahid Muhammad2; Jutima Simsiriwong1; Nima Shamsaei2; 1University of North Florida; 2Auburn University
    In this study, the high-cycle fatigue (HCF) and very-high cycle fatigue (VHCF) behavior of Inconel 718, nickel-based super alloys, manufactured via a Laser Beam-Powder Bed Fusion (LB-PBF) process is investigated, with emphasis on the influences of surface roughness and layer orientation. LB-PBF specimens are fabricated in two different build directions (vertical and 45° with respect to the build plate) and two surface finishes (as-built and machined surface conditions). Uniaxial fully-reversed (R = -1) constant amplitude force-controlled fatigue tests are conducted at various stress amplitudes utilizing a servo-hydraulic test system and an ultrasonic test system operating at 10 Hz and 20 kHz, respectively. Fractography analysis is performed using an optical microscope and a scanning electron microscope to identify microstructural features that initiate fatigue cracks in the specimens. Experimental results from LB-PBF Inconel 718 specimens are presented and compared to those of wrought Inconel 718.

9:40 AM  
Static and Dynamic Mechanical Properties of Selective Laser Melted Ti-6Al-4V Solid Material Printed with Optimized Argon Flow: Oscar Quintana1; Robert Rybolt1; William Relue1; 1DePuy Synthes Joint Reconstruction
    Shielding gas flow has been found to affect the stability of the process and consequently the quality of AM components. In addition to provide an inert atmosphere during the printing process, the argon flow removes process by-products, such as spatter and smoke that take place during the selective laser melting. Inefficient argon flow results in the interaction of the laser beam with the by-products, thereupon re-deposition on the melt pool. This has a negative impact on the surface morphology and density of the parts. In this study we investigated two argon flows (optimized vs non-optimized) and their effects on the tensile, and surface finish on Ti-6Al-4V samples (stress relieved) with different size dimensions and printing directions (horizontal vs vertical). Additional fatigue testing showed that samples printed with optimized flow had a 66% higher fatigue strength. The effects of argon flow on density and metallurgical characteristics of samples were also discussed.

10:00 AM Break

10:20 AM  Invited
Microstructure Design for Optimizing Mechanical Performance of Additive Manufactured Metallic Alloys: Ayman Salem1; Daniel Satko1; 1MRL Materials Resources LLC
     The inherent fast cooling rates during additive manufacturing (AM) of metallic alloys result in uncertainty and anisotropy in the location specific (LS) material properties. Such unique material characteristics can be correlated to the LS microstructure compromising the spatial characteristics of various phases (e.g size, morphology, and crystallography) and defects ( e.g. size, morphology etc). To enable certification of AMed parts for flight critical application, uncertainty in the LS properties need to be understood and quantified which can be achieved via understanding of LS microstructure evolution which can ultimately lead to tailoring the microstructure to achieve desired part performance. In this talk, a summary of microstructure-property correlations will be presented for commonly AMed Ti6Al4V, AlSi10Mg, 316L and novel titanium superalloys (e.g. beta Ti185) and aluminum superalloys (e.g Al-Zr). Various material properties will be presented including tensile and fatigue responses with correlations to as-built and tailored (i.e. designed) microstructures.

10:50 AM  
Optimization of Additively Manufactured Low Carbon Steels for Fatigue-critical Applications: Matthew Ryder1; Colt Montgomery2; Michael Brand2; Robin Pacheco2; John Carpenter2; Peggy Jones3; Diana Lados1; 1Worcester Polytechnic Institute, Integrative Materials Design Center; 2Los Alamos National Laboratory; 3General Motors Powertrain
    Additive manufacturing (AM) provides unparalleled flexibility in component design, and a comprehensive understanding of the AM parts’ behavior is imperative for their implementation in fatigue-critical applications. Two low carbon steels fabricated by Laser Powder Bed (LPB) have been investigated in this study – in both as-fabricated and heat treated conditions – and compared to their wrought counterparts. Build parameters have been selected through meltpool geometry optimization, and used in the fabrication of tensile, fatigue, and fatigue crack growth specimens. Microstructure, yield and tensile strengths, and hardness have been evaluated for all materials and conditions. Residual stresses have been predicted using DANTE® simulations, and experimentally measured via x-ray diffraction, the contour method, and notch clamping on fatigue crack growth (compact tension) specimens. Through systematic high-cycle fatigue (R=-1) and fatigue crack growth (R=0.1, 0.8) testing and characterization, crack initiation and propagation mechanisms have been identified and used in the process-microstructure-performance optimization.

11:10 AM  
Fatigue Crack Growth Behavior of DED Type 304L Stainless Steel: Christine Smudde1; Christopher San Marchi2; Christopher D'Elia1; Michael Hill1; Jeffery Gibeling1; 1University of California, Davis; 2Sandia National Laboratory, Livermore
    While additive manufacturing (AM) offers technological advancements supporting innovative engineering design, it also introduces challenges in fatigue critical applications. Due to the highly localized heating and the resulting temperature gradients of the manufacturing process, AM materials have unique microstructures and significant residual stresses that influence mechanical properties, including fatigue behavior. In this study, fatigue crack growth resistance of AM type 304L stainless steel produced by directed energy deposition was evaluated. Increasing and decreasing alternating stress intensity factor tests were conducted to provide a complete profile of fatigue crack growth behavior. In addition, constant alternating stress intensity factor tests were used to explore variations in crack growth rates at different locations in the build. Assessments of microstructural features and residual stress in AM type 304L through electron backscatter diffraction imaging and slitting measurements, respectively, support a more complete understanding of the factors affecting the material’s fatigue crack growth resistance.

11:30 AM  
Effect of Laser Shock Peening Processing Parameters on the Microstructure, Residual Stress, and Fatigue Behavior of Additive Manufactured CoCrMo Alloy: Micheal Kattoura1; Boetang Twum Donkor2; Jie Song2; Jan Kaufman3; Seetha Ramaiah Mannava2; Vijay Vasudevan2; 1LSP Technologies Inc.; 2University of Cincinnati; 3Institute of Physics of the Czech Academy of Sciences
    The effect of Laser Shock Peening (LSP) on the microstructure, residual stress, and fatigue behaviour of Additive Manufactured (AM) CoCrMo Alloy was investigated. Three LSP processing parameters were studied to optimize the laser peening process 1) sacrificial layer: vinyl tape versus aluminum tape, 2) shift between two peening layers, and 3) laser wavelength: infrared (IR) laser versus second harmonic generation (SHG) laser. In all studied laser peening conditions, laser peening induced a Strain-Induced Martensitic Transformation (SIMT) shifting the initially FCC structure to HCP+FCC structure at the surface. Laser peening converted the high tensile residual stresses created by the AM process to high compressive stresses that protects the material against different type of metal failures. The laser peened samples showed increase in the yield strength by around 15%. Laser peening improved the fatigue life of AM-CoCrMo by 10x to 15x of that of the as-built samples.