Segregation-induced grain-boundary precipitation during early stages of liquid-metal embrittlement of an advanced high-strength steel

Y. Ikeda, H. C. Ni, A. Chakraborty, H. Ghassemi-Armaki, J. M. Zuo, R. Darvishi Kamachali, Christoph Robert Eduard Maass

Research output: Contribution to journalArticlepeer-review

Abstract

Liquid-metal embrittlement (LME) of galvanized (Zn-coated) advanced high-strength steels is a long-known problem in materials science. Here we reveal the initial microstructural processes underneath the Zn-coating that lead to LME-microcrack initiation in the steel substrate. We track the microstructural evolution during the first tens of milliseconds and find pronounced signatures of Fe-Zn intermetallic precipitation in both ferrite grain boundaries and at internal ferrite-oxide phase boundaries. In concert with novel CALPHAD-integrated density-based thermodynamic modelling, we demonstrate that Zn-rich intermetallic phase-nucleation can occur at markedly low processing temperatures due to a segregation transition. We show that a small Zn-enrichment caused by Zn bulk-diffusion during the initial temperature rise in a joining process is sufficient to induce the segregation transition and subsequent nucleation of Fe-Zn intermetallic grain-boundary phases, which the experiments link to crack initiation sites. These findings direct focus onto LME-controlling microstructural and thermodynamic phenomena at temperatures below the ductility trough and the austenite formation temperature.

Original languageEnglish (US)
Article number119243
JournalActa Materialia
Volume259
DOIs
StatePublished - Oct 15 2023
Externally publishedYes

Keywords

  • grain boundaries
  • liquid-metal embrittlement
  • resistance spot welding
  • steels

ASJC Scopus subject areas

  • Electronic, Optical and Magnetic Materials
  • Ceramics and Composites
  • Polymers and Plastics
  • Metals and Alloys

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