Additive Manufacturing Fatigue and Fracture: Effects of Surface Roughness, Residual Stress, and Environment: Session I
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; Steve Daniewicz, University of Alabama; Mohsen Seifi, ASTM International/Case Western Reserve University
Monday 8:30 AM
March 20, 2023
Room: 22
Location: SDCC
Session Chair: Nik Hrabe, National Institute of Standards and Technology
8:30 AM Invited
Fracture and Adhesion of Cold Sprayed HY80 Steel: Luke Brewer1; Christopher Roper1; Anita Heczel1; 1University of Alabama
This talk describes the first mechanical behavior results for cold sprayed HY80 steel. While cold spray is now progressing well for additive repair of aluminum structures, the approach for high strength steels is just beginning. We have recently demonstrated the ability to successfully cold spray 4340 and HY80 steels using a combination of high pressure cold spray and laser assisted cold spray. We are now turning our attention to the mechanical behavior of these materials. In particular, we will be describing the ductility, impact fracture energy, and adhesion of HY80 steel deposits onto HY80 wrought material. The microstructure of cold sprayed steel resembles that of other cold sprayed material in that it is bimodal with highly deformed prior particle centers ringed with ultrafine-grained recrystallized grains. The ductility is controlled by a competition between stress concentrators produced by micro-porosity and micro-scale regions which lack metallurgical bonding between prior particles.
9:00 AM
Fatigue Behavior of Fastener Holes in High-strength Aluminum Plates Repaired by Additive Friction Stir Deposition: Ismael Hidalgo1; Paul Allison1; Brian Jordon1; Malcolm Williams1; Jacob Williamson2; Jacob Strain2; 1Baylor University; 2The University of Alabama
This present study will characterize the potential for solid-state additive manufacturing techniques, namely additive friction stir deposition (AFSD), in repairing high-strength aluminum alloy 7050. This study uses a blended-out center hole geometry to simulate mechanically or corrosively damaged material that commonly occurs around fastener holes. The microstructure of the repaired specimen will be characterized to evaluate the repair interface and the effect of heat input during processing on the substrate material. Monotonic and fatigue properties will be evaluated for repaired and unrepaired specimen to quantify the structural performance of the repairs. Post-testing fractography will elucidate the failure mechanisms from both cyclic and overload testing to allow for an understanding on the weaknesses and strengths of each process in repairing of AA7050. As such, this study will demonstrate the potential for solid-state manufacturing to return damaged components back to service.
9:20 AM
The Influence of Powder Reuse on the Mechanical Properties of Laser Powder Bed Fused Stainless Steel 316L: Rory Douglas1; Robert Lancaster1; Thomas Jones2; 1Swansea University; 2Rolls-Royce
The use of additive manufacturing (AM) for the fabrication of production parts is expanding. This has been driven by the improvements and optimisation of AM, as well as the unique design or re-design potential that AM can facilitate. Laser powder bed fusion (L-PBF) is an AM technique that can be used to create close to fully dense metal parts in near net geometries. To maintain financial competitiveness with alternative manufacturing techniques, it is common to reuse the powder feedstock in L-PBF across multiple builds. Through powder reuse, it is possible for the properties of the powder feedstock to shift. If this shift is great enough, it may have a knock-on effect upon part properties and performance. In this research, the evolution of L-PBF stainless steel 316L powder after different levels of recycling has been investigated, with a particular emphasis on how powder evolution influences the component’s final cyclic properties.
9:40 AM
An Acoustic Emission Monitoring Method during LPBF Processing for Detection of Microdefects: Kaita Ito1; Rinako Kokaji2; Masahiro Kusano1; Makoto Watanabe1; Takayuki Shiraiwa2; Manabu Enoki2; 1National Institute for Materials Science; 2The University of Tokyo
A novel acoustic emission monitoring method is presented for microdefect detection during laser powder bed fusion processing. This method enables accurate mapping of the occurrence time and location of microdefects. Even in one-time process in which multiple objects with different laser irradiation power and scanning speed are fabricated at the same time, it is possible to identify which object generated the AE by simple measurement using few sensors. Comparison of the observation results of the fabricated objects by X-ray CT and the detection history of AE events revealed that microcracks can be best detected by AE measurement among various types of defects during building. This method enables simple and real-time monitoring of production quality regardless of the material, size, and shape of the modeled object.
10:00 AM Break
10:20 AM Invited
Nondestructive Inspection for Structural Cold Spray Repairs: Brandi Briggs1; Mackenzie Perry2; Dustin Avery2; Jay Waterman2; Bobbie Diedrich1; 1Naval Air Systems Command Aircraft Division; 2Naval Surface Warfare Center Carderock Division
Additive manufacturing technologies, such as cold spray, are of interest to the Naval Air Systems Command Aircraft Division (NAWCAD) and the Naval Surface Warfare Center (NSWC) as a part repair technique. To date, cold spray has been used as a repair method to restore geometrical features for proper fit and installation, but has not been approved for structural restoration. To qualify this repair technique for structural applications, the defects that cause critical failures of these materials need to be identified and an inspection technique developed to detect critical defects in repaired parts. This presentation will discuss the work completed by NAWCAD and NSWC as part of the Solid State Structural Repair Program to develop nondestructive inspection (NDI) procedures for prototype structural repairs. Results of manufacturing physical inspection standards specific for cold spray repairs, effects of defects mechanical testing, and detectability of these defects with several inspection techniques will be presented.
10:50 AM
Comparison of Hydrogen-Metal Interactions in Additively Manufactured and Wrought 17-4PH via Thermal Desorption Spectroscopy Methods: Zachary Harris1; Alfredo Zafra2; Lauren Singer3; Emilio Martinez-Paneda2; John Scully3; James Burns3; 1University of Pittsburgh; 2Imperial College London; 3University of Virginia
Understanding hydrogen-metal interactions in additively manufactured (AM) materials is critical for the safe implementation of AM in components where environment-assisted cracking (EAC) is a pertinent failure mode. In this study, the hydrogen uptake, diffusivity, and trapping behavior of wrought and selectively laser melted (SLM) 17-4PH steel after a range of post-build thermal treatments (involving various combinations of solution annealing, hot isostatic press, and aging to the H900 or H1025 temper) is assessed using thermal desorption spectroscopy. Results demonstrate that each SLM 17-4PH condition consistently exhibits a lower hydrogen content and faster hydrogen diffusivity than comparable wrought material. Interestingly, only minor differences in hydrogen trapping behavior are observed between comparable wrought and SLM 17-4PH. These results are coupled with EAC measurements on the tested alloys to identify the factors responsible for the observed increase in EAC kinetics for SLM 17-4PH, focusing specifically on the role of microstructural differences.
11:10 AM Invited
Defect-sensitive Fatigue Design in Additive Manufacturing: Flaw Size Effects in Ultrasonic Fatigue of Laser Powder Bed Fabricated Al-10Si-Mg Alloys: Anthony Spangenberger1; Timothy Piette1; Bernd Schönbauer2; Diana Lados1; 1Worcester Polytechnic Institute; 2University of Natural Resources and Life Sciences, Institute of Physics and Materials Science
Additive manufactured (AM) materials frequently contain process-specific flaws that can result in early fatigue crack initiation and reduced fatigue lives. A quantitative understanding of the relationship between defect size and fatigue strength is therefore critical to design structural AM components. Fatigue testing of laser powder bed (LPB) Al-10Si-Mg specimens with polished surfaces and small drilled holes was conducted in the very-high cycle regime using ultrasonic frequencies. Fatigue strength sensitivity to initial flaw size was exhibited both by cracks naturally initiated from lack-of-fusion pores in smooth specimens and those with artificial flaws. Comparison with the Murakami model indicates that adequate fatigue strength predictions are made for both natural and artificial flaws. Complementary near-threshold ultrasonic fatigue crack growth tests were further conducted to establish an upper bound on the defect size sensitivity of the fatigue strength (long crack growth threshold). Recommendations will be made for fatigue design using fracture mechanics-driven methodologies.
11:40 AM
Mechanical Properties of Binder Jet Printed 17 – 4 Precipitation Hardened Martensitic Stainless Steel: Jayaraj Radhakrishnan1; Punit Kumar2; Alexis Bryl3; Jim Mckinnell3; Upadrasta Ramamurty1; 1Nanyang Technological University; 2Lawrence Berkeley National Laboratory; 3HP Inc.
The microstructure and mechanical properties of 17-4PH martensitic stainless steel fabricated using binder jet printing (BJP) were investigated with emphasis on high cycle fatigue (HCF) resistance. Porosity was varied by either controlling process parameters or by hot isostatic pressing. The tensile strength and ductility rise asymptotically with the decrease in porosity, until a critical fraction is reached. While the high cycle fatigue behavior was enhanced by the reduction in porosity, HIP results in a fatigue strength that is similar to CM alloy. Over-aging of the alloy improves its fatigue resistance due to higher stress intensity threshold for crack initiation. These variations are rationalized by recourse to analysis of the microstructure-crack interactions and was found that crack closure mechanisms are dominant at the fatigue crack tip of the over-aged microstructure. Significance of size rather than overall fraction of pore on the fatigue resistance of BJP 17-4PH alloys is highlighted.