Dissimilar micro beam welding of titanium to Nitinol and stainless steel using biocompatible filler materials for medical applications

Abstract

In the present investigation, thin sheet geometries of commercially pure titanium (cp, grade 4) are butt-welded to AISI 316L stainless steel as well as Nitinol by means of micro electron beam welding using filler materials. In order to avoid mixing of the base materials, the refractory metals tantalum, niobium and hafnium are applied as intermediate layers. Owing to the biocompatibility of these filler materials, the final products are suitable for medical technology applications. In combination with low energy inputs and precise beam alignments, it is demonstrated that high-quality and crack-free joints can be produced using micro electron beam welding. The welded joints are analysed using nanoindentation to identify critical weld areas, e.g. high concentrations of intermetallic compounds, and to evaluate the compatibility of the base and filler materials. To correlate the hardness mappings with the microstructural evolution of the welds, an exemplary joint is analysed by means of electron backscatter diffraction and energy dispersive X-ray spectroscopy with special emphasis on intermixing and the formation of intermetallic compounds. Based on the generated hardness mappings as well as the ultimate tensile strengths of the joints, it will be concluded which filler material provides the most promising results for the given material combinations.

Dissimilar Laser Beam Welding of Titanium to Stainless Steel Using Pure Niobium as Filler Material in Lap Joint Configuration

“…Dissimilar welded joints have the potential to combine the individual properties of different metals and, thus, generate various functional and economic advantages. In particular, hybrid parts made of commercially pure titanium (cp-Ti) and stainless steel are of high relevance in manifold industrial sectors, for example, the chemical, energy, and medical technology industries [1,2]. However, dissimilar fusion welding of cp-Ti to stainless steel is limited by thermophysical and chemical incompatibilities [1,3].…”

“…Nevertheless, the aforementioned material combinations do not exclusively involve biocompatible materials and are consequently unsuitable for medical technology applications. In a recent study by Wiegand et al [2], pure Nb was identified as a promising interlayer material for dissimilar welding of cp-Ti to stainless steel. By micro-electron beam welding, it was possible to achieve tensile strengths of up to 394 MPa in butt joint configuration.…”

“…The present investigation seeks to build on this study and addresses the intermixing of a Nb foil into a cp-Ti/Nb/316L dissimilar weld in a lap joint configuration. Complementary to the study by Wiegand et al [2], in which the two base materials were completely separated by the filler material, the study at hand serves to evaluate the intermixing of the materials and the influence on the weldability and mechanical properties of the joints. Furthermore, the consideration of the lap joint and the utilization of a pulsed laser beam system can potentially generate further opportunities for a transfer into current medical technology applications.…”

Obtaining of combined titanium-steel structures by electron beam freeform fabrication using niobium and copper interlayers

“…It`s implementation makes it possible to increase the installation and repair work manufacturability. Refractory metals such as vanadium [8][9][10][11][12][13][14], niobium [15][16][17][18][19][20][21][22][23] and tantalum [10,15,24,25] can be used for deposition on titanium alloy during additive forming. However, the use of tantalum may cause technological problems due to the large difference in melting temperatures.…”

“…However, according to scienti c papers [12,13,33,34], the formation of unfavourable ω-phase is revealed only in the Ti-V system. In the Ti-Nb system the formation of ω-phase is not observed [15,[16][17][18][19][20][21][22][23]. In addition to the formation of ω-phase, the creation of the unmixed region with zones of high and low titanium content is an important feature of the Ti-V system [14].…”