Obtaining NiTi by powder metallurgy

Abstract

Several alloys present the shape memory effect and among them, the equiatomic NiTi alloy, nitinol, is the most important one. It is usually used in general engineering and also in biomedical applications, in the fabrication of orthodontic wire, stents and Judet staples. Although a considerable amount of these biomedical devices is utilized in Brazil and a fraction of it is already made here, all nitinol used is bought abroad. Thus, it is important to develop the necessary know-how to fabricate NiTi wire and sheet. It would mean less importation with job creation and wealth generation for the country. This work proposes to obtain nitinol by powder metallurgy with subsequent plastic work. Compaction behaviour of the alloy, the rule of time and temperature during the sintering process and porosity volume as a function of the plastic work will be studied. On the purpose of eliminating porosity a second route will be also studied, involving pre-sintering, plastic deformation and final sintering. Precipitation of deleterious secondary intermetallic phases is seen as the most challenging obstacle during sintering. Characterization will involve mechanical and shape memory properties. Tensile tests, metalography and microscopy, thermal analysis and X ray diffraction will be used for characterization. (AU)