Additive Manufacturing: Processing, Microstructure and Material Properties of Titanium-based Materials: Session III
Sponsored by: TMS Titanium Committee
Program Organizers: Ulf Ackelid, Freemelt AB; Ola Harrysson, North Carolina State University; Peeyush Nandwana, Oak Ridge National Laboratory; Rongpei Shi, Harbin Institute of Technology
Tuesday 2:00 PM
October 19, 2021
Room: A120
Location: Greater Columbus Convention Center
Session Chair: Ola Harrysson, North Carolina State University
2:00 PM
Examining the Role of Parent Grain Orientations on the Texture and Physical Properties of Additively Manufactured Ti 6-4 Alloys: Michael Hjelmstad1; Pat Trimby1; 1Oxford Instruments
It is well established that additively manufactured Ti 6-4 grows from the melt with cubic beta-grains building epitaxially on underlying beta-grains. These beta-grains typically have a strong <100> texture aligned with the build direction and upon cooling, largely transform to the hexagonal alpha-phase. Using electron backscatter diffraction (EBSD) data of the final alpha-dominated microstructure, recent developments have made it possible to reconstruct the parent grain orientations based on the crystallographic relationship between parent beta grains and daughter alpha variants.Here we present a new, commercially available technique for the rapid and effective reconstruction of parent microstructures and demonstrate the application to some electron powder bed fusion (ePBF) manufactured Ti 6-4 samples. The results indicate the importance of the prior beta-grain microstructure, not only for its control of the resulting alpha-texture, but also in determining the elastic and deformation properties of the final Ti 6-4 sample.
2:20 PM
On the Use of Defects as Microstructural Informants in EBM Ti-6Al-4V: Katie O'Donnell1; Maria Quintana1; Matthew Kenney1; Peter Collins1; 1Iowa State University
Additive manufacturing processes of metallic materials involve complex physics and often the generation and/or retention of various defects (e.g., pores, keyholing). Defects are perceived as undesirable as they significantly affect key properties. Thus, in-situ monitoring and/or post-deposition processes are typically undertaken to avoid their formation or eliminate them. However, these otherwise bad actors can act as 'informants', revealing information about the temperature fluctuations, phase transformations, and stresses that occur, both locally and in the part as a whole. Microstructural, crystallographic, compositional, and morphological analysis of defects in electron beam powder bed printed Ti-6Al-4V parts, as well as knowledge of their mechanisms of formation, among other aspects, has been used to reveal key information about the physical mechanisms undergone by the material during the build process, including the relationship between local thermal stresses and cyclic phase transformations, melt pool fluid flow, and grain growth and formation.
2:40 PM
Use of Small Geometry Specimens to Determine the Fracture and Fatigue Crack Growth Properties of Additively Manufactured Ti-6Al-4V via DED Technique for Repair: Sammy Ojo1; Sulochana Shrestha1; Joseph El Rassi1; Manigandan Kannan1; Gregory Morscher1; Andrew Gyekenyesi1; Onome Scott-Emuakpor1; 1University of Akron
Ti-6Al-4V is a critical material for aerospace applications where fatigue crack growth and fracture properties are considered as critical mechanical properties. Repair methodologies are being considered for complex parts such as an integrally blade rotor via directed energy deposition additive manufacturing. A study was undertaken to assess the anisotropic fracture and fatigue crack growth properties of Ti-6Al-4V fabricated by DED AM method using notched compact test specimens. These specimens were cut from DED repaired and mildly heat-treated specimens. Because these small, sub-specimens of pure DED AM material were machined from 50/50 stock/DED AM repaired coupons from another study. Full field displacements were measured via digital image correlation while direct current potential drop was incorporated to monitor crack growth. To gain insight into failure mechanisms and microscopic features of the studied materials, fractured surfaces and polished section were examined, thereby, establishing a correlation between the resultant mechanical properties and microstructural features.
3:00 PM
Vibration Bending Fatigue Analysis of Additively Repaired Ti-6Al-4V Airfoil Blades: Lucas Smith1; Onome Scott-Emuakpor2; Joy Gockel3; Dino Celli2; Brian Runyon2; 1Ohio Aerospace Institute; 2Air Force Research Laboratory; 3Wright State University
Repairing airfoil blades is necessary to extend the life of turbine engines. Directed energy deposition (DED) additive manufacturing (AM) provides the ability to add material at a specific location on an existing component. In this work, AM repairs on Ti-6Al-4V airfoil blades were analyzed to determine what effect the repair will have on the blade performance in high cycle vibration fatigue testing. Targeted sections were cut out of airfoil blades near high stress locations and repaired using DED. To understand the defects that arose with this type of repair, computed tomography imaging was used to quantify the defects from the AM process. The blades were then tested until failure using vibration bending fatigue to simulate turbine engine loading conditions. Results suggest that understanding the impact of internal and surface level defects arising from the AM process is critical towards the implementation of AM repair in aerospace components under fatigue loading.
3:20 PM
Influence of Foreign-Object Damage on the High Cycle Fatigue Properties of Direct Energy Deposition Repaired Ti-6Al-4V: Sulochana Shrestha1; Manigandan Kannan1; Gregory Morscher1; Andrew Gyekenyesi2; Onome Scott-Emuakpor3; 1University of Akron; 2Ohio Aerospace Institute; 3Aerospace Systems Directorate
Additive Manufacturing (AM) approaches based on Direct Energy Deposition (DED) show promise as tools for repairing damaged Integrally Bladed Rotors (IBRs/blisk) which would otherwise require either an expensive replacement or a complicated repair. For the implementation of such repair approaches, proper assessment of material properties should be done under various scenarios. One key concern is the high cycle fatigue (HCF) related failures of IBR due to Foreign Object Damage (FOD) from ingested debris. FOD induces premature crack initiation resulting in unpredictable and accelerated failure of components. This study focuses on the influence of FOD in wrought annealed and DED repaired Ti-6Al-4V using wire feedstock. FOD was simulated by high-speed impacts of steel spheres on the flat surface of the thin, rectangular HCF coupons prior to testing. The impact created stress risers caused a marked reduction in fatigue life as compared to non-impacted coupons.