Alloying and aging treatment effect on the shape memory and damping properties of Cu-13Al-4Ni alloys

Abstract

Copper-based shape memory alloys (SMAs) are gaining attention as materials that require a good damping property in high temperature applications because they exhibit high damping properties during martensitic transformation and have an effective energy dissipation. However, copper-based SMAs such as the ternary alloy Cu-Al-Ni are not easily deformed in the lower temperature martensitic phase which can be attributed to brittleness induced by coarse grain size, high degree of order and elastic anisotropy. Hence, this study aimed to improve the properties of Cu-13Al-4Ni SMAs by addition of fourth alloying element and aging treatment that provides a significant effect on the microstructures and properties of the alloys. In this research, Cu-13Al-4Ni-X alloys with the addition of the fourth additional elements (X=titanium, cobalt or boron) were prepared by casting. The as-cast alloys were then homogenized at 900°C and followed by an aging treatment at 150°C, 200°C and 250°C for 24 hours. The transformation temperatures and microstructure characteristics of Cu-Al-Ni-X SMAs were investigated via differential scanning calorimetry (DSC), scanning electron microscopy (SEM) coupled with energy dispersive spectroscopy (EDS) and x-ray diffraction (XRD). The hardness of these alloys was determined using Vicker’s hardness tester. The shape memory effect was determined by compression test using an Instron universal testing machine. The damping property was measured by dynamic mechanical analysis (DMA) technique. The results revealed that the addition of titanium to the Cu-Al-Ni alloy led to the formation of X-phase which consists of intermetallic compounds of NiTi and AlTi2 that refined the microstructures. On the other hand, addition of cobalt changed the morphologies of the phases with formation of ?2 phase which improved the ductility of the quaternary alloy. Addition of boron to Cu-Al-Ni alloy led to the formation of secondary phases which also refined the microstructures. Among the three element additions, Co, B and Ti, it was found that the alloy with 0.7% of Co addition at aging treatment of 150°C for 24 hours showed the best shape memory effect with 100% recovery followed by Cu-13Al-4Ni-0.7Ti at aging temperature of 200°C with 97.5% recovery. However, the Cu-13Al-4Ni-0.7Ti at aging temperature of 200°C has the best damping properties with 0.18 internal friction followed by Cu-13Al-4Ni-0.7Co at aging temperature of 150°C with 0.1 internal friction. The findings showed that both of these alloys are good candidates for damping application.