Dam** characteristics of Ti₅₀Ni_49.5Fe_0.5 and Ti₅₀Ni₄₀Cu₁₀ ternary shape memory alloys

Abstract

The dam** characteristics of Ti₅₀Ni_49.5Fe_0.5 and Ti₅₀Ni₄₀Cu₁₀ ternary shape memory alloys (SMAs) have been systematically studied by resonant-bar testing and internal friction (IF) measurement. The dam** capacities of the B19′ martensite and the B2 parent phase for these ternary alloys are higher than those for the Ti₅₀Ni₅₀ binary alloy. The lower yield stress and shear modulus of these ternary alloys are considered to be responsible for their higher dam** capacity. For the same ternary alloy, the B19/B19′ martensite and R phase also have a higher dam** capacity than does the B2 parent phase. In the forward transformations of B2 → R, R → 519′, and B2 → 519′ for Ti₅₀Ni₅₀ and Ti₅₀Ni_49.5Fe_0.5 alloys, the dam** capacity peaks appearing in the resonant-bar test are attributed to both stress-induced transformation and stress-induced twin accommodation. The lattice-softening phenomenon can promote the stress-induced transformation and enhance the dam** capacity peaks. The Ti₅₀Ni₄₀Cu₁₀ alloy had an unusually high plateau of dam** capacity in the B19 martensite, which is considered to have arisen from the easy movement of twin boundaries of B19 martensite due to its inherently very low elastic modulus. The peaks appearing in the IF test for the Ti₅₀Ni₄₀Cu₁₀ alloy are mainly attributed to the thermal-induced transformation due to T ⊋ 0 during the test.