D. C. Dunand, Northwestern University, Evanston, IL
This paper presents a review of processing, structure and properties of porous/foamed NiTi for both medical and actuation applications. For medical applications, the low stiffness, high surface area (allowing bone ingrowth) and superelasticity/shape memory of porous NiTi, beside its established biocompatibility, makes it attractive for bone implants. For actuation, the high surface area permits rapid heat transfer to the foam, thus allowing for fast shape-memory actuation.
Processes are mostly based on powder metallurgy with (i) elemental powders via self-propagating high-temperature synthesis or (2) pre-alloyed powders with partial sintering in the presence of spaceholders. These can be temporary and be removed early during the sintering process (e.g. ammonium carbonate), or permanent and removed in a second step after densification (e.g. NaF or NaCl). A few processes use liquid NiTi, where pores are created by spaceholder removal after infiltration, or by evolution of dissolved gases. In many cases, shape-memory or superelastic properties are reported for this foams, provided the process did not alter the composition.
This presentation will provide a review of processing, structure and properties of porous/foamed NiTi for both medical and actuation applications. For medical applications, the low stiffness, high surface area (allowing bone ingrowth) and superelasticity/shape memory of porous NiTi, beside its established biocompatibility, makes it attractive for bone implants. For actuation, the high surface area permits rapid heat transfer to the foam, thus allowing for fast shape-memory actuation.
