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A novel heterogeneous-structure (HS) twinning-induced plasticity (TWIP) steel containing alternating columnar grain (CG) and equiaxed grain (EG) domains was successfully fabricated via prestraining, partial recrystallization, and directional solidification. Compared with the traditional EG sample, the HS sample exhibited a better tensile strength–elongation combination (yield strength ≈ 263 MPa, ultimate tensile strength ≈ 573 MPa, total elongation ≈ 101.5%). The mutually constrained structure could effectively control the unique deformation modes of the EG and CG domains at different deformation stages. The HS sample exhibited stable and continuous plastic deformation owing to the timely release of localized high strain or stress, postponed plastic instability, and restrained crack propagation owing to the constrained structure. The stress relaxation was due to twinning and the effects of geometrically necessary dislocations, which accommodated deformation incompatibility. The improved mechanical properties of the HS sample were due to the persistent occurrence of the TWIP effect under very low to high strain levels during the entire deformation process, the effective grain boundary hardening in the EG domain, and the additional work hardening provided by the GNDs.

The effects of pore density and matrix on the quasi-static and dynamic compressive behaviours of the high porosity open-cell aluminium foams were examined. The results show that pore density has little effect on the collapse strength of the samples under quasi-static conditions. However, as the strain rate increases, the collapse strength decreases with increasing pore density. The different matrix material also shows distinct strain rate response characteristics, which is related to their respective microstructures. The strain-rate sensitivity is mainly attributed to the micro-inertia effect caused by the larger aspect ratio of the cell edges, which was verified by the more transverse elongation of the dynamic compression samples. Moreover, the energy absorption capacity is also discussed in the present paper.

The effects of pore density and matrix on the quasi-static and dynamic compressive behaviours of the high porosity open-cell aluminium foams were examined. The results show that pore density has little effect on the collapse strength of the samples under quasi-static conditions. However, as the strain rate increases, the collapse strength decreases with increasing pore density. The different matrix material also shows distinct strain rate response characteristics, which is related to their respective microstructures. The strain-rate sensitivity is mainly attributed to the micro-inertia effect caused by the larger aspect ratio of the cell edges, which was verified by the more transverse elongation of the dynamic compression samples. Moreover, the energy absorption capacity is also discussed in the present paper.

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. Two types of porous Cu–Al–Ni shape memory alloys (SMAs) are prepared using different raw materials. Their structures and damping properties are compared, which have important reference significance for follow–up research. The damping of the porous Cu–Al–Ni SMA prepared from Cu, Al, Ni powders is significantly improved by adding Ce element. Correlated mechanisms are discussed.

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. Internal friction (IF) in a Cu–Al–Mn shape memory alloy (SMA) is studied as a function of strain amplitude (SA). It is found that both the non‐isothermal IF and the isothermal IF show obvious dependence on SA. Based on transmission electron microscopy observation, correlated mechanisms are discussed in terms of the change of the density of moveable interfaces, the mergence of martensites, the de‐pinning of dislocations.

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 γ2precipitate 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.

The effect of heat treatment on the damping behaviour of a Cu–11.9Al–2.5Mn (wt%) alloy was investigated and correlated with the martensite microstructures. It is found that elevated quenching temperature and rapid cooling can give rise to increased damping capacity due to the formation of favourable martensite microstructures characterized by coarse twin boundaries and a high twin content. (© 2006 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

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 AlNb3phase in the Cu–Al–Mn matrix. Due to the pinning effect of the AlNb3phase 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. For the first time, the damping of a Cu–Al–Mn shape memory alloy is significantly improved by the combined use of parent phase aging and addition of Nb element. According to the evolution of microstructures, correlated mechanisms are explained in terms of the changes in martensitic transformation behaviors, contents of Al element and quenched‐in vacancies, interfacial mobility, and phase composition.