Tailoring the damping and mechanical properties of porous NiTi by a phase leaching process

A porous B2-NiTi compound with fine pore size and homogeneous pore distribution has been successfully fabricated by a novel phase leaching top-down process. In this process, NiTi-NiGd duplex pre-alloys were firstly prepared. Then NiGd phase was etched out in nitric acid solution, leaving NiTi to form pore structures. The pore size could be refined by increasing the cooling rate of the pre-alloys. The porosity could be tailored by changing the volume fraction of NiGd, which was related to the compositions of pre-alloys. The pore size can be refined to ∼0.27 μm in the sample with a porosity of 29%. This sample shows the highest damping capacity (0.08 at ambient temperature) and Young's modulus (6.2 GPa). These excellent damping and mechanical properties should be attributed to the enlargement of stress-strain localization areas of the refined pore structure. However, increasing the porosity to a further extent results in a larger pore size and degrades the damping property. The present homogeneous and fine porous NiTi is considered to be good candidates as damping materials in engineering application.