Heat treatment of additively manufactured cardiovascular CoCr stents

Aim of this thesis work is an experimental study concerning the heat treatment and characterization of additively produced CoCr stents and bulk samples. Additive manufacturing is a new technology which is also used in biomedical area. Stents produced by selective laser melting process have many advantages like manufacturing parts directly from powder, customized production and shape flexibility. Nevertheless, as-built AM stents have lack of some properties to be utilized in biomedical field. Heat treatment process should be suggested to improve mechanical properties of AM stents. The work has been focused to give sufficient ductility to stents produced additively. For this purpose, proper heat treatment temperatures are detected from both previous studies and DSC analysis. In addition, evolution from as-built condition to heat treated condition of stents has been investigated. Stents and bulk samples were produced according to two different scanning strategies with selected process parameters. In this context, effect of the strategies on the microstructure of the material has been examined. In addition, bulk samples and stents produced with the same parameters were compared within themselves. Thus, size effect has been also investigated comparing bulk and stent samples.

Obiettivo di questo lavoro di tesi riguarda la caratterizzazione microstrutturale e meccanica di parti prodotte con tecnologia additiva a letto di polvere in CoCr. La produzione di stent con tecnologie additive può portare ad alcuni vantaggi, tra cui la personalizzazione del componente e la flessibilità nella realizzazione di geometrie tridimensionali molto complesse. In questo lavoro si è studiato anche l’effetto dei trattamenti termici, necessari per garantire proprietà meccaniche adeguate, basandosi su informazioni fornite dalla letteratura e da misure calorimetriche, fatte appositamente sui campioni presi in esame. In particolare, è stato studiato l’effetto di alcune condizioni di processo differenti (effetto della strategia di scansione laser) e l’effetto dimensionale, confrontando campioni massivi e campioni sottili, quali stent.