Effect of Laser Surfacing on the Microstructure and Mechanical Properties of Ultrasonic Welded NiTi Joints

Sansan Ao, Chunjie Li, Wei Zhang, João Pedro Oliveira, Zhi Zeng, Zhen Luo

Research output: Contribution to journalArticlepeer-review

Abstract

In the present work, the effects of laser surfacing aiming at modifying the surface roughness on NiTi sheets prior to the application of ultrasonic welding (USW) were investigated. Three different configurations joining original and laser surfaced specimens were performed: original/original (referred as O/O), original/treated (referred as O/T), and treated/treated (referred as T/T). The influence of surface roughness on the interface formation, diffusion, and mechanical properties was investigated. It is observed that when both bonding surfaces becomes rougher (T/T configuration), the joint strength is the highest, followed by both smooth bonding surfaces (O/O configuration), and the strength of the joint is the lowest when only one of the bonding surfaces was roughened (O/T configuration), which is related to the degree of plastic deformation at the joining interface. The main joining mechanism of NiTi to the Al interlayer was a metallic bonding caused by shear plastic deformation and formation and growth of micro welds at the joining interfaces. Laser surfacing facilitates the metallic bonding, which is directly reflected in the change of the thickness of the Al interlayer after USW. This also helps to produce a mechanical interlocking at the interface, although there is no significant difference in the elemental diffusion. Interfacial failure occurred in all joints tested under different surface contact conditions and exhibited ductile-like fracture characteristics.

Original languageEnglish
Article number011003
JournalJournal of Manufacturing Science and Engineering, Transactions of the ASME
Volume144
Issue number1
DOIs
Publication statusPublished - 1 Jan 2022

Keywords

  • interface formation
  • joining mechanisms
  • laser surfacing
  • NiTi shape memory alloys
  • surface roughness
  • ultrasonic spot welding
  • welding and joining

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