Effects of postweld heat treatment on the phase transformation and mechanical behavior of NiTi ultrasonic spot welded joints with al interlayer

Chunjie Li, Sansan Ao, João Pedro Oliveira, Zhi Zeng, Huijie Cui, Zhen Luo

Research output: Contribution to journalArticlepeer-review

2 Citations (Scopus)

Abstract

The influence of postweld heat treatments (PWHTs) on the phase transformation characteristics, microstructural evolution, and mechanical properties of ultrasonic spot welded NiTi alloy with Al interlayer was investigated. At room temperature, the as-welded joints were fully austenitic, while the microstructure of welded joint after PWHT at 450°C consisted of a mixture of martensite and austenite. The transformation temperatures were found to increase after the PWHT. Transmission electron microscope analysis shows that Al3Ti intermetallic compounds were formed on the Al side of the Al/NiTi interface after the PWHT at 450°C for 90 min. Furthermore, finely dispersed nanoscale Ni4Ti3 precipitates were observed in the joint. These nanoscale precipitates resulted in an increase in the transformation temperatures and improved the mechanical properties of the PWHT material. During lap shear test, the as-welded samples failed in a brittle manner in the NiTi alloy, while the PWHT samples failed in the Al interlayer and exhibited ductile-like fracture characteristics.

Original languageEnglish
Article number101006
JournalJournal of Manufacturing Science and Engineering, Transactions of the ASME
Volume142
Issue number10
DOIs
Publication statusPublished - 1 Oct 2020

Keywords

  • joints
  • mechanical properties
  • NiTi shape memory alloys
  • phase transformation
  • postweld heat treatment
  • ultrasonic spot welding
  • welding and joining

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