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Porous Cu–Al–Ni shape memory alloys (SMAs) are fabricated via powder metallurgy method using Cu, Al, Ni powders and Cu–Al–Ni alloy powder as raw materials, respectively. It is found that the two kinds of specimens have similar macroscopic morphologies: connected pores are uniformly distributed in the Cu–Al–Ni matrix, forming a 3D network structure. By comparison, the specimen fabricated using alloy powder has much finer microstructures than the specimens fabricated using Cu, Al, Ni powders. After adding Ce element to the latter, the microstructure of the Cu–Al–Ni matrix is significantly refined because of the formation of Ce‐rich particles. Damping tests show that the latter has superior damping capacity than the former. With the increase of Ce content, the damping of the latter increases first and then decreases. When the Ce content reaches 0.05 wt%, the highest damping can be achieved. Correlated mechanisms are discussed based on the microstructural observations. [ABSTRACT FROM AUTHOR]

Strain amplitude (SA) dependence of internal friction (IF) in a Cu–Al–Mn shape memory alloy (SMA) is investigated. Microstructure observation is conducted with the aim to clarify related mechanisms. It is found that the IF measured during the continuous heating process shows a nonmonotonous dependence on SA, that is, the IF increases first and then decreases. The increase of IF can be attributed to the mergence of martensite laths promoted by the reorientation of martensite variants, whereas the decrease of IF is related to the decrease in the density of moveable interfaces. The isothermal IF measured at low temperatures increases monotonously with the increase in SA, because the density of movable interfaces and the sliding distance of these interfaces in the tangential direction increase. Thermal cycles can significantly improve the isothermal IF because of the annihilation of quenched‐in vacancies and the reorientation of martensite variants. At around 240 °C, the isothermal IF in all specimens shows a nonmonotonous dependence on SA, which can be ascribed to the dragging effect of quenched‐in vacancies on dislocations and the breakaway of dislocations from these vacancies when the SA is high enough. [ABSTRACT FROM AUTHOR]

It is recognized that both parent phase aging and element addition can dramatically enhance the comprehensive properties of Cu‐based shape memory alloys (SMAs). However, further in‐depth studies are still needed to clarify the detailed laws and mechanisms. Herein, the effects of parent phase aging and Nb element on the microstructure, martensitic transformation (MT), and damping behaviors of a Cu–Al–Mn SMA are systematically studied. It is found that both the damping at low temperatures and the height of internal friction peak arising from the reverse MT of the Cu–Al–Mn SMA can be improved by the parent phase aging due to the increase in interfacial mobility. When the aging temperature reaches 600 °C, the best damping can be obtained. Nb forms AlNb3 phase in the Cu–Al–Mn matrix. Due to the pinning effect of the AlNb3 phase on grain boundaries, the grains of the Cu–Al–Mn SMA can be remarkably refined. With the increase in Nb content, the damping of the 600 °C aged Cu–Al–Mn SMA increases first and then decreases. The associated mechanisms are discussed. This work aims to provide theoretical basis and technical support for the improvement of damping property of Cu‐based SMAs. [ABSTRACT FROM AUTHOR]

The grain-boundary relaxation as well as corresponding internal friction (IF) mechanism in Cu-based shape-memory alloy was investigated taking Cu-20.4Al-8.7Mn (at%) as an example. A relaxational IF peak was found at around 214 °C during the heating process, whereas the peak completely disappears during the subsequence cooling process. The IF peak with the activation energy and pre-exponential factor of 1.60 eV and 3.8 × 10−18, respectively, shifting towards higher temperature as the measuring frequency increased indicates that the peak correlates to a thermal-activation process. The results obtained revealed that the viscous sliding of the grain boundaries should be the operative mechanism for the appearance of the peak. However, the appearance of the γ2 precipitate particles formed during the heating process provides a reverse contribution to the peak, leading to the disappearance of the peak due to their pinning effect on the grain boundaries. [ABSTRACT FROM AUTHOR]