Fracture Behaviour of Nickel-Titanium Laser Welded Joints

Abstract

In this study, the effects of Nd:YAG laser welding on the fracture behavior of Ni-rich nickel-titanium sheets are analyzed by experimental investigations. The welding was carried out in open air conditions by using a special shielding/clamping system to avoid the chemical contamination of the molten zone and the formation of hot cracks. Mechanical tests of standard dog bone-shaped and single edge crack specimens were carried out to measure the stress-strain response and the fracture resistance of both the base and the welded materials. Furthermore, scanning electron microscopy observations of the fracture surfaces were carried out in order to better understand the failure mechanisms. Finally, systematic comparative studies between base and laser-welded materials were carried out.

Fiber laser welding of NiTi to Ti-6Al-4V

“…While similar welds NiTi/NiTi are well succeeded, joining these materials to others is not a simple issue, due to hightemperature diffusion with localized changes in chemical composition and the formation of brittle intermetallics [10][11][12].…”

“…Embrittlement occurs mainly due to high-temperature reaction of elements such as oxygen, nitrogen, and hydrogen. Brittle intermetallics like Ti 2 Ni and Ti 3 Ni can precipitate during solidification, having adverse effects on strength and shape memory characteristics [12,14]. This work aimed to analyze the possibility of welding NiTi to Ti-6Al-4V plates by laser in butt joint configuration.…”

Numerical modeling of heat transfer and fluid flow in hybrid laser–TIG welding of aluminum alloy AA6082

“…The benefits of hybrid welding arise due to synergy effect and interaction between two heat sources, i.e., laser and arc [1,7,3]. During laser and hybrid welding, a deep and narrow vapor filled cavity is created, the so-called keyhole, due to high-focused laser energy and thus allows for a much deeper weld penetration to be obtained [8,3,[9][10][11]. Metal vapors leaving the laser-generated keyhole are the main source of this laser-arc synergy when the arc and laser are in close proximity [3,5,1].…”

<i>In Situ</i> Structural Characterization of Laser Welded NiTi Shape Memory Alloys

“…Gugel et al [10] reported, for laser welded Ni-rich wires, a tensile strength up to 75% of the base material, as well as a pronounced SE up to 10 cycles. Maletta et al [11] evaluated the fracture behaviour of laser welded NiTi and reported very interesting results regarding tensile strength of welded joints. As a continuation of a previous study [9], Khan et al [12] analyzed the effects of laser processing on the transformation temperatures of Nitinol; their DSC results revealed additional high temperature transformation peaks that can be attributed to the local phase conversion induced by laser processing; these results were further corroborated with RT XRD analysis, showing only austenite in the base metal and added martensite peaks in the melted metal.…”