Additive Manufacturing Fatigue and Fracture V: Processing-Structure-Property Investigations and Application to Qualification: Titanium
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

Tuesday 8:30 AM
March 16, 2021
Room: RM 2
Location: TMS2021 Virtual

Session Chair: Nik Hrabe, National Institute of Standards and Technology (NIST)


8:30 AM  Invited
Implementing Processing Strategies and Unique Hot Isostatic Pressing Treatments to Control Microstructure, Defect Content, and Mechanical Properties of Electron Beam Melted Ti-6Al-4V: Jake Benzing1; Nikolas Hrabe1; Enrico Lucon1; Timothy Quinn1; Julius Bonini2; Magnus Ahlfors3; 1National Institute of Standards and Technology; 2Lucideon M+P; 3Quintus Technologies
    Materials of known, repeatable properties that are resistant to fracture are of prime importance for structural applications, but additively manufactured parts often contain internal voids and heterogeneities at the microstructural level which reduces strength and repeatability. Post-manufacture, hot isostatic pressing (HIP) treatments are commonly employed to seal the internal porosity. In this work, Ti-6Al-4V parts were manufactured with different melt model sizes to produce crystallographic textures that do not match the texture assumed for most Ti-6Al-4V AM parts (<001>β-fiber in the build direction). In addition, the parts were also subjected to three different HIP treatments, which are all effective in sealing internal porosity. HIP treatments were carried out at temperatures above and below the β transus for Ti-6Al-4V. The relationships between these processing and post-processing strategies on defect content, crystallographic texture, prior-β grain morphology, α-lath thickness, tensile properties, J-type fracture toughness, and high-cycle fatigue life will be presented.

9:00 AM  
Effect of Oxide and Hydroxide on Cold Spray of Titanium Particles: Mobin Vandadi1; Arvand Navabi1; Trevor Bond1; Nima Rahbar1; Winston Soboyejo1; 1Worcester Polytechnic Institute
    This paper presents results of a multi-scale study on mechanical behavior of Titanium powders in Cold Spray process. Effects of oxide and hydroxide layer on surface of particle are first studied using Molecular Dynamics simulations. Afterward, these results are used in Finite Element Simulation to study the cold spray process. Elastic moduli, toughness, and fracture energies of oxide and hydroxide layers are derived from MD and are input into FEA. Then, parameters such as particle size and oxide thickness are changed to understand their effect. A bi-linear Johnson-Cook model is used to predict deformation of Titanium and brittle cracking method is used for oxide and hydroxide parts. Results show that there is a portion of oxide and hydroxide layer which does not fail during the impact. Size of trapped section is computed as a function of other parameters. This result has important implications in the robustness of cold sprayed part.

9:20 AM  
The Inhomogeneous Microstructure and Properties of Ti-6Al-4V Additively Manufactured with Electron Beam Freeform Fabrication: Samuel Present1; Karen Taminger2; Chris Domack2; Kevin Hemker1; 1Johns Hopkins University; 2NASA Langley Research Center
    Electron beam freeform fabrication (EBF3) is a wire-fed directed energy deposition additive manufacturing process that emphasizes a high deposition rate and offers the capability to additively manufacture large-scale structural components in remote space environments. Despite its promise, the relationships between processing parameters, microstructure, and the mechanical properties of material produced by EBF3 are not well understood. This study was undertaken to characterize the inhomogeneous “fish scale” macrostructure of as-deposited Ti-6Al-4V that arises due to the unique thermal history of the EBF3 process. Temperatures in the heat affected zone of subsequent deposition beads exceed the beta transus temperature, which results in a periodic microstructure across the bulk material. The inhomogeneous microstructure gives rise to attendant inhomogeneous mechanical behavior. Location-specific elastic modulus, hardness, and strength were measured with nanoindentation. Fabrication of milli-scale tensile samples and digital image correlation facilitated mapping of strain localization and analysis of the overall response of Ti-6Al-4V builds.

9:40 AM  
Quantifying Layer Uniformity in Ti6Al4V Hybrid Additively Manufactured Samples Using Ultrasound: Luz Sotelo1; Cody Pratt1; Rakeshkumar Karunakaran1; Cody Kanger1; Michael Sealy1; Joseph Turner1; 1University of Nebraska Lincoln
    Hybrid additive manufacturing (AM) is an emerging approach to create functionally architected components based on microstructural changes, without drastically varying the material chemistry. However, methods of characterization and inspection for these components are limited to ensure they meet design requirements and are suitable for service throughout their life. It is necessary to incorporate material complexity considerations into model-based nondestructive evaluation (NDE). In this work, statistics-based ultrasonic NDE methods grounded in diffuse ultrasonic backscatter modeling are used to detect and quantify spatial variations imparted by a hybrid AM process (DED + milling). These methods were successfully implemented in self-evaluation as well as evaluation across an ensemble of Ti6Al4V samples. The results of this work are expected to inform future NDE strategies that are needed to enhance the performance of high-value components. The potential expansions and limitations of these methods are also discussed.