Abstract: Shape memory alloys (SMAs) are well-suited for vibration and noise reduction due to their outstanding mechanical and damping properties. However, their damping capacity is limited due to low-temperature stabilized thermoelastic martensite and constrained twin migration. This work designs nanoscale Nb phases to enhance the damping capacity and maintain a wide working temperature range of NiTiHf-based SMAs. The NiTiHf/Nb alloys containing spherical Nb phases demonstrate a 125 % improvement in internal friction (IF) and remain stable up to 400 K. Alloys with spherical Nb phases exhibit relatively high intrinsic IF, which is mainly attibuted to the high migration ability of martensitic twin boundaries. High-resolution transmission electron microscopy images and IF spectra suggest spherical Nb phases pro-vide additional dislocation damping effects and interface damping effects by inducing multiple types of dislocations near the multi-directional phase interfaces. These findings provide insights into the role of second-phase shape effect in damping properties and offer valuable guidance for designing ultra-high damping alloys.

Key words: Damping, Morphology effect, Nanoscale Nb phase, High-temperature shape memory alloys