Laser welding of H-phase strengthened Ni-rich NiTi-20Zr high temperature shape memory alloy

João Pedro Oliveira, Jiajia Shen, J. D. Escobar, C. A. F. Salvador, Norbert Schell, N. Zhou, O. Benafan

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Abstract

Laser welding of a Ni-rich NiTi-20Zr (at.%) high temperature shape memory alloy was performed. The starting base material was aged for 3 h at 550 °C followed by air cooling prior to welding to induce H-phase precipitation. Advanced microstructure characterization encompassing scanning and transmission electron microscopy, coupled with synchrotron X-ray diffraction, were used. Defect-free welds were obtained with a conduction welding mode. The weld thermal cycle altered the microstructure across the heat affected and fusion zones of the joints. The heat affected zone exhibited partial H-phase dissolution, causing a decrease in hardness. In the fusion zone, the H-phase fully dissolved, and the non-equilibrium rapid solidification conditions prevented the H-phase from re-precipitating during cooling, leading to a microstructure resembling that of an as-cast alloy with the same material composition. Mechanical testing revealed that the laser welded samples sustained stresses in the order of 500 MPa and exhibited stress-strain responses comparable to those of the unwelded base material. Thus, this initial study shows new possibilities for using advanced laser joining methods in these alloys.

Original languageEnglish
Article number109533
JournalMaterials and Design
Volume202
DOIs
Publication statusPublished - Apr 2021

Keywords

  • H-phase
  • High temperature shape memory alloys
  • Laser welding
  • NiTiZr
  • Rietveld refinement
  • Synchrotron X-ray diffraction

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