Variant selection and macrozone in Ti-6Al-4V walls during laser hot wire direct energy deposition

Published

November 17, 2024

Author(s)

Rajib Halder, Souvik Sahoo, Jake Benzing, Alec Saville, Anthony Rollett

Abstract

Additively manufactured Ti-6Al-4V (Ti64) wall structures used as various structural aerospace components suffer from the spatial variations in mechanical properties, texture-mediated anisotropy, and macrozones that degrade the mechanical performance, especially fatigue, under certain service conditions. The development of texture and macrozone formation in titanium alloys are closely related to the variant selection during the phase transformation in the additive manufacturing process. In this study, electron backscatter diffraction (EBSD) was employed to investigate the variant selection mechanism and macrozone formation criteria in single- and multi-wall specimens manufactured with laser hot wire directed energy deposition (LHW-DED). Variant analysis revealed that strong variant selection with a preferred selection of the type 2, variant occurs in both single and multiwalls. The primary factor dictating the selection of the variant boundaries was found to be the cooling rates. The main underlying mechanism governing variant selection to compensate for transformation strain during solid-state phase transformation was determined to be the triple-alpha variants clustering of Category I. Evidence of thermal stress playing a minor role in variant selection was also observed. Furthermore, location-specific variant analysis revealed that the white bands (microstructural bands with distinct etching contrast) on the walls consist of fewer variants than the bulk. The macrozones formation criteria are proposed and the effect of macrozones on mechanical behavior is discussed in conjunction with the Schmid factor analysis of variants with respect to different loading directions. The density of macrozones was also quantified.

Citation

Journal of Materials Research and Technology

Volume

33

Pub Type

Journals

Download Paper

https://doi.org/10.1016/j.jmrt.2024.11.061

Local Download

Keywords

Variant selection, Macrozones, Ti-6Al-4V (Ti64), Laser hot wire directed energy deposition (LHW-DED), Wall structure

Citation

Halder, R. , Sahoo, S. , Benzing, J. , Saville, A. and Rollett, A. (2024), Variant selection and macrozone in Ti-6Al-4V walls during laser hot wire direct energy deposition, Journal of Materials Research and Technology, [online], https://doi.org/10.1016/j.jmrt.2024.11.061, https://tsapps.nist.gov/publication/get_pdf.cfm?pub_id=958448 (Accessed December 12, 2024)