Processing of NiTi Polymer Composites

NiTi shape memory alloy composites are highly attractive for application in the medical field due to a good biocompatibility. Polymer coatings on NiTi can be used to impede the critically discussed dissolution of Ni ions. Nevertheless, one key aspect for the fabrication of hybrid NiTi polymer structures is a sufficient adhesion between both types of material. Both materials strongly differ in terms of mechanical and chemical properties and as a consequence, interface engineering is required to provide a good adhesion and to prevent delamination processes. In the present work, we show how different types of NiTi surface treatments improve the adhesion in hybrid NiTi polymer structures fabricated by injection moulding. Initially, pseudoelastic NiTi ribbons were prepared by mechanical and chemical polishing, plasma treatments and application of surface agents. Surface coatings (polyamide PA6) were applied by subsequent injection moulding. The adhesion quality was evaluated by mechanical pull-out testing. Our results show that NiTi surfaces after mechanical polishing only provide a very poor pull-out strength. The adhesion quality can be strongly improved by the application of silane surface agents on electropolished NiTi surfaces.