Extrusion of nickel–titanium alloys Nitinol to hollow shapes

Nickel–titanium alloys, Nitinol, with their special characteristics such as like superelasticity and shape-memory effect have achieved significant importance in recent years. The major part of superelastic Nitinol alloys applies at present in medical technology. For this application particularly, tube products are used. The present production of Nitinol tubes usually takes place via forging, gun-drilling and hot/cold drawing procedures. For the production of solid and hollow semi-finished materials by extrusion, which enable a substantially larger cross-section of reduction in one step, compared to the above mentioned process, so far no fundamental realizations have been presented. This paper describes the results of the hot extrusion of Nitinol alloys. The deformation resistance of these alloys can be determined experimentally, provided that the extrusion forces are known. The deformation resistance of Nitinol and the tool stresses in relation to the extrusion temperature and ram velocity, and billet preparation and process details, will be reported. These results are of great importance in two aspects: the evaluation of the extrusion process and the design of extrusion tools.