Additive Manufacturing Fatigue and Fracture: Effects of Surface Roughness, Residual Stress, and Environment: Session III
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
Tuesday 2:30 PM
March 21, 2023
Room: 22
Location: SDCC
Session Chair: Mohsen Seifi, ASTM International/Case Western Reserve University
2:30 PM Invited
Assessment of Fatigue Evolution and Damage Tolerance in Additive Manufactured Metals: Mustafa Awd1; Daniel Kotzem1; Felix Stern1; Mirko Teschke1; Jochen Tenkamp1; Frank Walther1; 1TU Dortmund University
The microstructure, defects and roughness in additive manufacturing (AM) processes determine the fatigue performance in engineering applications. Modern testing strategies and measurement techniques enable accurate monitoring of the influence of process-induced characteristics on the fatigue behavior. Intermittent fatigue testing revealed the interaction between microstructure, local porosity and fatigue crack initiation until very high cycle fatigue (VHCF) region. For 316L, AlSi, TiAl and Ni alloys, the effect of defects, building direction and stress ratio on fatigue evolution was investigated. The fatigue strength could be correlated with the hardness and the effective defect or pore size relative to load direction using Murakami-Noguchi concept. By elastic-plastic modification by J-integral of Heitmann, the effect of microstructure on cyclic stress-strain behavior and fatigue damage tolerance could be proofed. The studies reveal the potential to enhance the fatigue lifetime and damage tolerance based on comprehensive structure-property relationships to be integrated in uniform fatigue damage tolerance approaches.
3:00 PM
Role of the Oxide Layer in Cold Sprayed Metallic Structures: Mobin Vandadi1; Nima Rahbar1; Winston Soboyejo1; 1Worcester Polytechnic Institute
The lightweight of aluminum alloys and incredible properties of titanium alloys make them desirable for many applications. Additive manufacturing is one of the fastest and easiest methods for making new parts and cold spray is a new method in this field. In this method, micron size particles are accelerated towards the substrate, and this will result in bonding. There are many parameters that are influential in efficiency of this method such as the velocity and size of particles, temperature, etc.; however, a less studied parameter is the oxide layers on the substrate and powders. The oxide layer is a hard and brittle layer that does not bond as well as the underlying metal. In this work, first the failure of the oxide layers of both aluminum and titanium is studied using molecular dynamics. Next, FEA is used to study the effect oxide on the efficiency of the cold spray deposition.
3:20 PM
Evaluating Residual Stress Effects on Fatigue Crack Growth Behaviour of AM Stainless Steel Processed via DED and PBF: Christine Smudde1; Christopher San Marchi2; Michael Hill1; Jeffery Gibeling1; 1University of California, Davis; 2Sandia National Laboratories, Livermore
Additive manufacturing technologies, such as directed energy deposition (DED) and powder bed fusion (PBF), offer unique advantages for innovative engineering design. However, they also introduce challenges in fatigue critical applications due to process induced residual stress in as-built material. In this study, fatigue crack growth behaviour of type 304L stainless steel produced by DED and PBF methods was evaluated and compared. Fatigue crack growth rates were explored over a range of applied alternating stress intensity factors in the near threshold regime and were quantitatively corrected for the influence of residual stress using residual stress intensity factors determined using online compliance. Specimens oriented for crack growth parallel and perpendicular to the build direction provided insight into the anisotropy of residual stress and resulting fatigue behaviour. Finally, assessments of variations in crack growth rates due to crack tip interactions with microstructure were made using images of grain morphology surrounding crack path profiles.
3:40 PM
Tunable Fatigue Performance in Laser Powder Bed Fusion Titanium Alloy via Laser Shock Peening: Nik Hrabe1; Tom Berfield2; Jake Benzing1; Newell Moser1; Orion Kafka1; Nicholas Derimow1; 1National Institute of Standards and Technology; 2University of Louisville
Laser shock peening (LSP) shows potential to improve fatigue performance of additive manufacturing metals through controlled manipulation of residual stress with little effect on surface roughness or microstructure. In this work, LSP was used to manipulate the residual stress profile of titanium alloy (Ti-6Al-4V) specimens manufactured via laser powder bed fusion (PBF-L). Vertically oriented, cylindrical specimens were built in a single build using standard melt parameters and powder. Specimens were tested without machining in axial stress-controlled high-cycle fatigue (R= 0.1, ASTM E466) in four material conditions: as-built (no surface treatment or heat treatment), stress relieved (600 °C, 3 hours, vacuum, furnace cool), and two laser shock peening parameter sets (varying number of passes). Residual stress (contour method), porosity (XCT), surface roughness (profilometry and XCT), fractography (SEM), and microstructure (EBSD) evaluations were performed within specimen gauge sections for all four conditions.
4:00 PM Break
4:20 PM
The Influence of Sample Thickness, Residual Stress, and Surface Condition on Ultrasonic Fatigue Behavior of LPBF 316L: Megan Trombley1; John Allison1; 1University of Michigan
We have previously shown that the ultrasonic fatigue response of additive manufacturing samples of 316L steel exhibits a pronounced effect of as-built sample diameter. Laser powder bed fusion (LPBF) specimens built on a Concept Laser M2 have shown an increase in fatigue life and fatigue strength as the diameter of specimens is reduced from 5.0 mm to 2.5 mm and 1.5 mm. The current work investigates the influence of surface condition and residual stress on these results. Axial residual stress depth profiling, stress relief annealing, and varying degree of surface removal and polishing are used to quantify how surface roughness and residual stress impact the sizing effects observed. This work will help inform the ICME framework and design guidelines to better correlate lab testing to component applications.
4:40 PM
Influence of Post-Processing Techniques on Process-induced Defects in AM AlSi10Mg and CP-Ti: Austin Ngo1; Hannah Sims1; John Lewandowski1; 1Case Western Reserve University
Additive Manufacturing (AM) processes have versatile capabilities but are susceptible to the formation of non-equilibrium microstructures, process-induced defects, and porosity, which have deleterious effects on the mechanical performance of AM-processed structural materials. A variety of post-processing techniques were investigated as a method of reducing process defect severity and improving mechanical properties. Specimens of Laser Hot Wire CP-Ti and Laser Powderbed Fusion AlSi10Mg were fabricated over a range of process parameters, followed by post processing in different ways to illustrate beneficial changes in mechanical performance. Fracture surfaces were analyzed using OM and SEM methods. The effects of post processing techniques on both LHW CP-Ti and LPBF AlSi10Mg will be discussed in terms of mechanical properties and fractography.
5:00 PM
Fatigue of L-PBF Ti-6242 under Different Heat Treatment Processes, and Comparisons to Ti64: Amir Hadadzadeh1; Mahdi Habibnejad Korayem2; Reza Molaei1; 1University of Memphis; 2AP&C Advanced Powder and Coating, a GE Additive Company,
While titanium and its alloys are known for their excellent creep resistance as well as high strengths, their applications are mostly limited to about 400℃. However, a recently manufactured alloy, Ti6242 (Ti-6Al-2Sn-4Zr-2Mo-0.08Si) can be used for long-term high temperature applications up to 540℃, making it a better candidate for aerospace applications such as jet engine components and industrial gas turbines. Despite the higher strength, this alloy is highly sensitive to the heat treatment processes. 8 different heat treatment procedures were designed and applied to the L-PBF samples under monotonic loading, and the results indicated that different processes can significantly affect strength and ductility of the specimens.Due to the cyclic nature of the applied stresses in the operational environments, their cyclic and fatigue properties are of utmost important considerations. Specimens fabricated with different heat treatments will be tested under both elastic and plastic loads and the results will be compared.
5:20 PM Invited
Development of Metal Powders for Additive Manufacturing Applications: Lorena Perez1; Luke Brewer1; 1University of Alabama
The growth of additive manufacturing (AM) applications has led to a demand for alloy powders suited for these advanced processing methods. Atomization is the most common process for producing powders for AM. Most often the powders used for AM are pre-existing alloys developed for conventional manufacturing processing methods, e.g. wrought plate. The processing conditions during AM, i.e., rapid solidification and high-temperature gradients, lead to microstructures and mechanical properties different from the wrought material. Therefore, to explore the full potential of AM and to achieve mechanical properties equivalent or superior to those of conventional manufacturing methods, the development of novel AM-suitable alloy powders is critical. In this talk, we will provide a comprehensive look into the recent advances in the field of alloy design of new alloy powders and modification of pre-existing metallic powders produced by gas atomization to advance the mechanical properties of components built up by AM.