The effects of rare earth element Sm on the microstructure, mechanical properties, and shape memory effect of the high temperature shape memory alloy, Cu-13.0Al-4.0Ni-xSm (x = 0, 0.2 and 0.5) (wt.%), are studied in this work. The results show that the Sm addition reduces the grain size of the Cu-13.0Al-4.0Ni alloy from millimeters to hundreds of microns. The microstructure of the Cu-13.0Al-4.0Ni-xSm alloys are composed of 18R and a face-centered cubic Sm-rich phase at room temperature. In addition, because the addition of the Sm element enhances the fine-grain strengthening effect, the mechanical properties and the shape memory effect of the Cu-13.0Al-4.0Ni alloy were greatly improved. When x = 0.5, the compressive fracture stress and the compressive fracture strain increased from 580 MPa, 10.5% to 1021 MPa, 14.8%, respectively. When the pre-strain is 10%, a reversible strain of 6.3% can be obtained for the Cu-13.0Al-4.0Ni-0.2Sm alloy.

In this study, the influence of an aging treatment on the shape memory effect and martensitic transformation was investigated in an Fe–Mn–Al–Ni alloy by adding a small amount of Nb and C elements. Results show that the aging treatment can significantly improve the shape recovery rate of the alloy. In the bending test with 4% deformation, after aging at 200 °C for 1 h, the recovery rate increased from 20 to 45%, and it further increased to 51% after the two-step aging treatment at 800 and 200 °C. The high-temperature in situ X-ray diffraction and atomic force microscope were used to reveal the shape memory effect between room temperature and 400 °C in this alloy due to γ′→α transformation. The microstructure of aged specimens was investigated using transmission electron microscopy. With the extension of the aging time from 0.5 to 6 h, the size of NiAl precipitation gradually grew from 9 to 32 nm, and the distribution became more uniform. Meanwhile, the NbC particles were found in the two-step aging treatment alloy, which was the key to improving the shape memory effect.

High-strength steels are widely used in various mechanical production and construction industries for their low cost, high strength and high toughness. Among these, bainitic steels have better comprehensive performance relative to martensite and ferrite. In this paper, from the point of view of its microscopic fine structure and mechanical properties, the high-carbon silicon-containing steel Fe-0.99C-1.37Si-0.44Mn-1.04Cr-0.03Ni was austenitized at high temperature after a brief isothermal treatment at 280 °C and is briefly reviewed. We have used EBSD, TEM and 3D-APT to observe a unique transformation in which high-carbon silicon-containing steels form nanostructured bainite with nanometer widths. Intriguingly, as the isothermal duration decreases, the beam bainite width becomes increasingly finer. When the beam bainite width falls below 50 nm, there is a sudden shift in defect type from the conventional edge-type dislocations to a defect characterized by the insertion of a semi-atomic surface in the opposite direction, which leads to different degrees of reduction in the micro- and macro-mechanical properties of high-carbon silicon-containing steels from 1754 MPa to 1667 MPa. This sudden change in the sub-structural properties is typical of the reverse Hall–Petch effect.