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

Abstract

proposal I-20160912 ; 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. ; publishersversion ; published

Topics

• microstructure
• phase
• x-ray diffraction
• hardness
• transmission electron microscopy
• defect
• precipitation
• joining
• rapid solidification