Analysis of formation and growth of the σ phase in additively manufactured functionally graded materials

Lourdes D. Bobbio, Brandon Bocklund, Ashley Reichardt, Richard Otis, John Paul Borgonia, Robert Peter Dillon, Andrew A. Shapiro, Bryan W. McEnerney, Peter Hosemann, Zi Kui Liu, Allison M. Beese

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31 Scopus citations


This study focuses on the formation of the σ phase in three functionally graded material (FGM) systems made by additive manufacturing (AM): stainless steel 420 (SS420) to V to Ti–6Al–4V, Ti–6Al–4V to V to stainless steel 304 L (SS304L), and SS420 to V. Directly joining Ti–6Al–4V and stainless steel may result in the formation of brittle Fe–Ti intermetallics. This study investigates the potential use of V as an intermediate element between terminal alloys of Ti–6Al–4V and stainless steel. Experimental analysis of the elemental and phase composition revealed that different amounts of σ phase were present in the three FGM systems at locations with similar elemental compositions. Computational studies were performed to simulate the thermal history, phase transformation kinetics, and σ phase growth within these FGMs. The computations suggested that, at the conditions studied, the σ phase should nucleate faster and grow to a larger volume fraction in the SS420–V alloy than the SS304L–V alloy, contrasting with experimental observations. Instead, experimental analysis confirmed that the disparate growth of σ phase in the FGMs was due differences in cracking during fabrication, resulting in different amounts of time spent at the elevated temperatures conducive to σ phase growth in each of the samples.

Original languageEnglish (US)
Article number151729
JournalJournal of Alloys and Compounds
StatePublished - Jan 25 2020

All Science Journal Classification (ASJC) codes

  • Mechanics of Materials
  • Mechanical Engineering
  • Metals and Alloys
  • Materials Chemistry


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