Abstract: TiNi-based shape memory alloys (SMAs) have been used as damping materials to eliminate noise and mechanical vibration. However, their application is limited by low working temperatures and damping capacity. In this work, two novel Ti-Zr-Hf-Ni-Co-Cu high entropy shape memory alloys (HESMAs) with different transformation temperatures and damping properties were investigated. The results show that Ti₂₅Zr₈Hf₁₇Ni₃₀Co₅Cu₁₅ has superior damping performance arising from martensitic transformation, shape memory effect (thermal cycle at constant load) as well as superelasticity. Compared to traditional TiNi-based SMAs, the as-cast HESMAs exhibit a much higher ultrahigh yield strength (∼2 GPa) and storage modulus (∼50 GPa). The high configuration entropy of the HESMAs with high uneven internal stress and severe lattice distortion is revealed as the underlying mechanisms governing distinctive damping performance. The effects of high configuration entropy and microheterogeneity on the martensitic transformation behavior and damping performance of HESMAs are clarified in this work, which provides a basis for designing alloys with superior damping properties.

Key words: High entropy shape memory alloy, Internal friction, Damping, Configuration entropy, Martensitic transformation