Product Code: ICAL08_M601

Laser Welding of Shape Memory Alloys for Medical Applications
Authors:
Ronny Pfeifer, Laser Zentrum Hannover E.V.; Hannover Germany
Dirk Herzog, Laser Zentrum Hannover e.V.; Hannover Germany
Andreas Ostendorf, Laser Zentrum Hannover e.V.; Hannover Germany
Oliver Meier, Laser Zentrum Hannover E.V.; Hannover Germany
Heinz Haferkamp, Laser Zentrum Hannover E.V.; D 30419 Germany
Thomas Goesling, Medizinische Hochschule Hannover; Hannover Germany
Christian Muelller, Medizinische Hochschule Hannover; Hannover DC Germany
Christof Hurschler, Medizinische Hochschule Hannover; Hannover Germany
Presented at ICALEO 2008

Shape memory alloys (SMA) are of increasing interest in research and industry due to their outstanding properties. Besides the shape memory effect (SME), these properties include high mechanical strength and biocompatibility, which is of high importance for medical applications.
The SME offers new possibilities in the design of implantable components, e.g. in the field of fracture healing. Conventional implants which are connected to bones cannot change mechanical properties such as stiffness, length and torsion resistance without additional surgeries once implanted. Implants made of SMA instead may change their properties by contactless application of heat from the outside by induction.
This paper presents a possible design for an osteosynthetic implant made from NiTi elements. Obviously, it is necessary to machine these elements from the NiTi sheet material by suitable processing methods that allow for a high precision and keeping the SME. Therefore, laser welding has been investigated due to its local energy distribution and small heat affected zones. Temperature measurements and metallographic investigations are presented to show the affected area where the SME is lost. Using a specially designed induction coil, the remaining SME is evaluated and the shape change is detected and the design of the implant is iteratively improved.