Control of porosity and superelasticity of porous NiTi shape memory alloys prepared byhot isostatic pressing

Abstract

Porous Ni-rich NiTi SMAs have been successfully prepared from elemental Ni and Tipowders, using capsule-free hot isostatic pressing processing. The fabricated alloys haveisotropic and uniform pore distributions of spherical pores ranging from 50 to200 µm. The porosities of these NiTi alloys range from 30 to 40% by volume. The microstructure,martensitic transformation behaviors and mechanical properties of the fabricated porousNiTi SMAs aged under different conditions were studied. It has been found that the phasetransformation behaviors of porous NiTi SMAs are similar to those of conventionally castNi-rich NiTi alloys. It is encouraging that the porous NiTi SMAs exhibit excellentsuperelasticity at room temperature after the appropriate thermomechanical treatment.Experimental results reveal that the superelasticity, which is controlled by the porecharacteristics, such as pore shape, pore size and pore distribution, is important forimproving the toughness, elastic properties and compression strength of the porous NiTiSMAs.