Submicron-porous NiTi and NiTiNb shape memory alloys with high damping capacity fabricated by a new top-down process

In this paper, submicron-porous NiTi and NiTiNb shape memory alloys were firstly fabricated by a new top-down process, including solidified phase controlling and etching process. These porous alloys possessed fine pore size (~0.4. μm) and homogeneous pore distribution. The mechanical properties of these porous alloys were similar to those prepared by conventional powder metallurgy techniques or bottom-up process. However, the damping capacity of the submicron-porous NiTi was ~0.07 and 40% higher than the counterparts produced by the conventional powder metallurgy techniques. The damping capacity of the submicron-porous NiTiNb was ~0.18 and 50% higher than its dense counterpart. The internal friction value at austenite state for submicron-porous NiTiNb was ~0.04 and 200% higher than its dense counterpart, 300% higher than submicron-porous NiTi. The high damping capacity of these submicron-porous shape memory alloys was considered to be caused partly by their fine pore structures, which enhanced the stress concentration and the microplastic deformation or collapse of thin nodes. These porous shape memory alloys exhibited moderate stiffness as well as high damping capacity and high specific strength, making them good candidate as practical engineering damping materials.