Dynamic mechanical damping analysis of up/step-quenched Cu-Zn-Sn-based shape memory alloys

Abstract

The effect of thermal quenching procedures on the damping properties of Cu-Zn-Sn-based SMAs is reported. Three compositions of Cu-Zn-Sn-based SMAs designated A (Cu-15.6Zn-12.1Sn), B (Cu-26.1Zn-9.3Sn), and C (Cu-29.6Zn-8.9Sn) samples produced by the casting process were subjected to direct quenching, up-quenching, and step-quenching treatments. The microstructure of the samples was examined using the backscattered electron microscope with fixtures for energy-dispersive spectroscopy analysis. The damping properties were assessed on a dynamic mechanical analyzer and presented in terms of tan delta. The microstructures of Cu-Zn-Sn-based SMAs consist of γ-Cu5Zn8 and Cu4 major phases containing some black dot precipitation and a small amount of white circular precipitates in the parent phase. For the A alloys, the step-quenched samples exhibited the highest damping capacity with peak internal friction of 0.041 at 37℃, which is greater than 0.028 at 37℃ and 0.26 at 25℃ obtained for the up-quenched and direct-quenched samples respectively. The step-quenched B alloys show the highest damping capacity with peak internal friction of 0.104 at 227℃, which is far greater than 0.053 at 23℃ and 0.034 at 35℃ obtained for the up-quenched and direct-quenched samples respectively. For the C alloys, the up-quenched samples show the highest damping capacity with peak internal friction of 0.053 at 235℃, which is greater than the peak values of 0.037 at 238℃ obtained for the step-quenched samples. Direct-quenched samples gave the lowest damping capacity with a peak value of 0.027 at 235℃. In general, step-quenching treatment effectively improved the damping properties of Cu-Zn-Sn-based SMAs.