MeTiWeld

Nitinol, an alloy of approximately 50% titanium and 50% nickel commonly used in medical technology, exhibits two important properties: The shape memory effect and superelasticity. In many industrial applications, it is necessary to combine stainless steel and nitinol while retaining the superelastic properties.

The project aims to demonstrate that micro-beam and laser beam welding, using biocompatible additives, can be used to produce a welded joint between the two materials that can withstand a tensile stress in the range of the superelastic plateau of nitinol.

Stainless steels, titanium and titanium alloys as well as the shape memory alloy Nitinol are metallic materials frequently used in medical technology which exhibit biocompatibility. Nitinol, as a phase consisting of approx. 50% nickel and 50% titanium, is characterized by the fact that it undergoes defined changes in shape during certain externally stimulated transformations or, depending on conditioning, can withstand elastic elongations of up to approx. 10% without undergoing significant plastic deformation. While dissimilar welds, both on titanium and on non-steels, can be produced by laser or electron beam welding with the same tensile strength of the base material, and nitinol also has about 80% of the tensile strength of the base material in the dissimilarly welded state, dissimilar joining of the metals mentioned causes considerable problems. When these materials are welded, embrittling intermetallic phases are formed, so that fusion welding processes can only be used to a limited extent, if at all, and only with significantly reduced joining properties.

The use of products with welded joints of titanium and stainless steel, as well as titanium and nitinol without the previous limitations of mechanical-technological properties, is of great interest to a large number of SMEs in the medical and microsystems technology industries. Therefore, within the scope of the project it shall be demonstrated that with the help of micro-electron and laser beam welding using biocompatible filler metals from the group of refractory metals, a welded joint can be produced between the above-mentioned materials which can withstand a tensile stress in the range of the superelastic plateau of nitinol. In the course of the investigations, particular emphasis will be placed on the avoidance of embrittling intermetallic phases and the biocompatibility of the resulting joint.