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, J. P. Oliveira, Zhi Zeng, Huijie Cui, Zhen Luo

Research output: Contribution to journalArticle

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 degrees 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 degrees C for 90 min. Furthermore, finely dispersed nanoscale Ni(4)Ti(3)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

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

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