Additive Manufacturing Fatigue and Fracture IV: Toward Confident Use in Critical Applications: Processing-Structure-Property-Performance 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; Steve Daniewicz, University of Alabama; Nima Shamsaei, Auburn University; John Lewandowski, Case Western Reserve University; Mohsen Seifi, ASTM International/Case Western Reserve University
Tuesday 2:00 PM
February 25, 2020
Room: 10
Location: San Diego Convention Ctr
Session Chair: Mohsen Seifi, ASTM International
2:00 PM Invited
Fatigue and Interfacial Fracture Behavior of Cold Spray Deposited Material for Additive Repair: Luke Brewer1; William Story1; Benjamin White1; J Jordon1; 1University of Alabama
This presentation will discuss the use of cold spray deposition for solid state structural repair of high strength aluminum alloy structures. High strength aluminum alloys, such as AA7075 and AA2024, are not readily repaired by fusion-based welding. High quality aluminum alloy material can be deposited by cold spray in relatively large volumes, but the key mechanical properties must be assessed and optimized for use in structural repairs. In particular, adhesion and fatigue response are critical for structural repair of aerospace structures. We will present a new method for measuring interfacial fracture toughness of cold spray deposited AA7075 material. This method shows the impact of substrate preparation and residual stress on the interfacial fracture toughness. In addition, we will present results on the fatigue behavior of cold sprayed material, both as free-standing and in the repair of fastener holes. The interplay between fretting fatigue damage and crack propagation will be discussed.
2:30 PM
Expedited Optimization of AM Materials Using Miniaturized Testing: Jonathan Torres1; Ali Gordon2; 1Bucknell University; 2University of Central Florida
The small punch test (SPT) has been developed for the purpose of characterizing materials which are scarce or costly by using reduced-size test samples. While limitations exist for utilizing the SPT for material characterization, the test economizes resources in optimizing processing for additive manufacturing (AM). Several AM materials were tested under varying conditions and stages of processing. Parameters such as build orientation, post-processing variations, and testing conditions are shown to cause notable differences in sample responses. Conditions varied of samples include variations in both sample preparation and testing conditions, including both monotonic and cyclic loading. Comparisons are made between tests to find the effects of each varied condition, and trends are correlated to show the capabilities of the SPT. Fractography results are shown exploring fracture patterns which vary depending on test conditions such as load and control type and are shown to be dependent on manufacturing orientation and processing conditions.
2:50 PM
Fatigue Behavior and Failure Mechanisms of Laser Beam Directed Energy Deposited Inconel 718: Rakish Shrestha1; Alexander Johnson2; Pooriya Nezhadfar1; Nima Shamsaei1; 1Auburn University; 2Trivector Services Inc
Due to its superior mechanical properties at a wide range of temperatures, Inconel 718, a nickel based super alloy, is being extensively used in jet engines. However, due to its high hardness, Inconel parts are known for their poor machinability. With the opportunity to fabricate near net shaped parts via additive manufacturing, Inconel 718 has been given more prominence lately. In this study, cyclic deformation and fatigue behavior of Inconel 718 fabricated using laser beam directed energy deposition process at room and elevated temperatures are investigated. Fully-reversed, strain-controlled fatigue tests were conducted at ambient temperature and 650 °C under various strain amplitudes. The grain structure evolution due to cyclic deformation at elevated temperature is characterized using microscopy. Fractography analysis is employed to capture failure mechanisms and identify internal defects responsible for the crack initiation.
3:10 PM
Effects of Internal Porosity and Crystallographic Texture on Fatigue Crack Growth Rate of Electron Beam Melted (EBM) Titanium Alloy (Ti-6Al-4V): Nik Hrabe1; Jake Benzing1; Timothy Quinn1; Lucas Koepke1; Jolene Splett1; 1National Institute of Standards and Technology - Boulder
The effects of internal pores and crystallographic texture on ASTM E647 fatigue crack growth rate (R = 0.1) of EBM Ti-6Al-4V were investigated by studying material in the as-built and HIPed conditions as well as in two orthogonal crack growth directions with respect to the build direction. HIPing sufficiently reduced porosity (x-ray CT), and unexpected texture variation (EBSD) was observed for this material (i.e. NOT <100>β-fiber in the build direction). Significant effect on the onset of unstable crack growth was observed due to internal porosity and texture variation.
3:30 PM Break
3:50 PM Invited
Fatigue Crack Growth Properties of Selective Laser Melting Produced Nickel and Titanium Based Alloys: Jamie Kruzic1; Halsey Ostergaard1; Tarik Hasib1; 1University of New South Wales
Selective laser melting (SLM) produces unique microstructures (e.g., epitaxial columnar grains, texture, etc.) that influence mechanical properties. In this work, the fatigue crack growth properties of SLM produced Alloy 718 and Ti-6Al-4V were examined at room temperature with various cracking orientations relative to the build plane and various post heat treatments, including hot isostatic pressing (HIP). Both materials showed very weak anisotropy in their 25°C fatigue growth rates. For Alloy 718, HIPing was found to recrystallize much of the columnar microstructure and mostly eliminate the weak anisotropy in growth rates seen for the non-HIPed structure; however, growth rates and thresholds remained well below that of wrought material. At 650˚C, anisotropy in fatigue crack growth rates became significant. For Ti-6Al-4V, fatigue thresholds increased with increasing alpha lath thickness and decreasing strength. Microstructure analysis, fractography, and observations of crack profiles were used to understand the microstructure influence on fatigue crack growth.
4:20 PM
Fatigue Properties of Additively Manufactured Ti-6Al-4V-ELI Material Hot Isostatically Pressed at Temperatures Above the Material’s Beta Transus Temperature: Julius Bonini1; Ho Mei Leung1; Kevin Knight2; Bruno La Razer3; Magnus Ahlfors4; 1Lucideon; 2JTL America, Inc.; 3Zenith Tecnica; 4Quintus Technologies
Hot Isostatic Pressing (HIP) is known to improve the fatigue performance of Ti-6Al-4V castings, and can result in a significant reduction in porosity. It is often used as a post-processing step in Additively Manufactured (AM) Ti-6Al-4V-ELI components and has been shown to significantly affect microstructure and heal internal porosity and other defects. The effects of various HIP temperatures on AM Ti-6Al-4V-ELI materials as it relates to the fatigue performance will be assessed. HIP exposures at various temperatures above the beta transus temperature will be examined and compared to results previously obtained on as-built and standard HIP processed samples. Axial fatigue results with full S-N curves will be presented from specimens of Electron Beam Manufactured (EBM) Ti-6Al-4V-ELI in the various HIPed conditions. Microstructural effects of these exposures will also be examined and documented. Fracture surfaces of the specimens will also be evaluated to contrast the samples’ fracture modes.
4:40 PM
Implementing Processing and Post-processing Strategies to Control Microstructure, Defect Content and Mechanical Properties of Electron Beam Melted Ti-6Al-4V: Jake Benzing1; Nikolas Hrabe1; Tim Quinn1; Enrico Lucon1; Magnus Ahlfors2; 1National Institute of Standards and Technology; 2Quintus Technologies
The effects of processing and post-processing conditions on defect content, grain orientation, grain morphology, tensile properties and fracture toughness of Ti-6Al-4V parts (produced by electron beam melting - a powder bed fusion method) have been investigated. Changes in grain orientation from changes in scan length (distance the electron beam travels before turning around on a new track) were examined. Hot isostatic pressing (HIP) is a commercial post-processing step known to seal internal porosity in additively manufactured parts. In the present work, sub-Beta transus and super-Beta transus HIP treatments were employed to manipulate the size, orientation and morphology of grains in Ti-6Al-4V parts. The effects of microstructural variations and porosity on tensile properties and fracture toughness will be presented.
5:00 PM
Prediction of Mechanical Properties of Additively Manufactured Ti6Al4V Based on the Microstructure and Porosity Distribution: Mohamed Elkhateeb1; Yung Shin1; 1Purdue University
Additive manufacturing (AM) is mainly challenged by the existence of porosity and inhomogeneous microstructure in the fabricated parts. Prediction of the effects of such defects on the parts’ bulk behavior and fatigue life requires huge heterogeneous finite element models, which can make the computational cost prohibitive for large structures. In this work, the extended mechanics of structure genome (XMSG) is used as computationally efficient multi-scale homogenization scheme to predict the bulk behavior and fatigue life of AMed Ti6Al4V with porosity and having a heterogeneous microstructure. In the XMSG, homogenization was conducted on a structure genome, which contains the basic representative microstructural and porosity details, and does need updates with porosity growth and coalescence. The predicted results showed a very good agreement with the experimental results with a 94% reduction in the computational time compared with the corresponding heterogeneous models-based finite element simulations.