Three-dimensional chemical analysis of laser-welded NiTi–stainless steel wires using a dual-beam FIB

Abstract

The biomedical industry has an increasing demand for processes to join dissimilar metals, such as laser welding of NiTi and stainless steel wires. A region of the weld close to the NiTi interface, which previously was shown to be prone to cracking, was further analyzed by energy dispersive spectrometry (EDS) extended in the third dimension using a focused ion beam. As the spatial resolution of EDS analysis is not precise enough to resolve the finest parts of the microstructure, a new segmentation method that uses in addition secondaryelectron images of higher spatial resolution was developed. Applying these tools, it is shown that this region of the weld close to the NiTi interface does not comprise a homogeneous intermetallic layer, but is rather constituted by a succession of different intermetallics, the composition of which can be directly correlated with the solidification path in the ternary Fe-Ni-Ti Gibbs simplex.

Nickel-Titanium Alloys Welding of Thin Sheets Using GTAW: Comparative Study Between Similar and Dissimilar Welding with AISI 304 Stainless Steel

“…It is very important to note that most studies on similar and dissimilar welding involving NiTi SMA were performed with wires [7][8][9][10][11][12][15][16][17] and using the LBW process. There are only a few studies on thin sheets [18][19][20] and even fewer using simpler and less expensive processes, such as the gas tungsten arc welding (GTAW).…”

Welding and Joining of NiTi Shape Memory Alloys: A Review

“…This peculiar site for crack initiation and propagation was studied in more detail [175] by a new 3D-EDS technique combining both FIB and SEM. With such configuration it was possible to obtain multiple EDS spectra of the region of interest and different heights (steps of 100 nm, with a total of 352 EDS maps).…”

Enhanced quantification for 3D SEM–EDS: Using the full set of available X-ray lines

“…SEM–EDS mapping can be extended to three-dimensional (3D) microanalysis using a dual beam microscope formed by a SEM coupled to a focused ion beam (FIB) [15–17] . The geometry of acquisition is shown in Fig.…”

“…The analysed surface is surrounded typically by trenches, in which spurious X-rays may be emitted. Minimising these limitations during acquisition and through post-processing, 3D EDS by FIB/SEM was shown to be a powerful tool to enable a deep understanding of a sample [15,18] .…”