Zhang and colleagues investigated the effects of doping of rare earth element Sm on the structure, mechanical properties, and Shape Memory Effect (SME) of the Cu-13.0Al-4.0Ni alloy. They showed that it not only reduces the grain size but also it causes a 2H martensite to become a single phase martensite. In addition, it has been shown that, Sm doping greatly improved mechanical properties and the shape memory effect (SME) of the Cu-13.0Al-4.0Ni alloy. Their study recently appeared in the Journal Materials.
Shape memory alloys (SMA’s) are metals, which exhibit two very unique properties due to its reversible thermoelastic matensitic transformation: hyperelasticity, and the shape memory effect. These properties makes them suitable for sensing and drive applications. Some developed SMAs such as Ni-Ti have martensitic transformation temperature less than 100°C, which limits their further application. Thus, several studies are focusing on the application of SMAs at higher temperatures, and in particular, high temperature shape memory alloys (HTSMAs) have the potential to be used as solid-state actuators in high temperature fields of aerospace, nuclear power, fire, oil, and gas exploration.
At present, the Cu-Al-Ni alloy has become a potential HTSMA due to the low cost and outstanding properties of its single crystal. However, the severe brittleness of polycrystalline Cu-Al-Ni alloys limits its practical application, which is related to its large elastic anisotropy and large grain size. In recent years, powder metallurgy, rapid solidification, and alloying methods are all methods used for improving the mechanical properties and mechanical properties of alloys by reducing the grain size. Among them, the alloying method has the characteristic of simple equipment, and so the addition of the fourth element is considered to be an effective method to improve the mechanical properties of Cu-Al-Ni SMAs, with simple operation and convenient production.
Recent studies demonstrated that the addition of rare earth elements can change the microstructure and mechanical properties of Cu-Al-Ni SMAs. In addition, Zhang and colleagues previously conducted research on adding rare earth elements such as Gd and Nd to the Cu-13.0Al-4.0Ni alloy. Their results demonstrated that the addition of rare earth elements greatly improves the mechanical properties of the Cu-13.0Al-4.0Ni alloy. Now, they investigated the effects of doping of rare earth element Sm on the structure, mechanical properties, and SME of the Cu-13.0Al-4.0Ni alloy.
They first showed that the Sm addition reduces the grain size of the Cu-13.0Al-4.0Ni alloy from millimeters to hundreds of microns.
It also causes the 2H martensite in the Cu-13.0Al-4.0Ni alloy to disappear and become a single-phase 18R martensite, which is accompanied by the formation of a Sm-rich second phase (Cu-13.0Al-4.0Ni-xSm) in the process.
Additionally, they found that with the increase in Sm content to 0.5%, the compressive fracture strength and the compressive fracture strain of the sample also further increased to 1021 MPa and 14.8%, respectively.
“Compared with most non-rare earth elements, the rare earth element Sm can better improve the SME of the Cu-Al-Ni alloys, but its effect is not as good as that of the B element and the rare earth elements Gd and Nd.”— they said
Finally, they found significant improvement in mechanical properties and the shape memory effect (SME) of the Cu-13.0Al-4.0Ni alloy, due to fine-grain strengthening, which was enhanced by Sm doping. However, the rare earth element Sm cannot be added to the Cu-Al-Ni alloys without limitation, because as the Sm content in the alloy increases, the number of the Sm-rich second phase will also increase.
“The influence of a Sm-rich second phase on the mechanical properties of the Cu-Al-Ni alloys is not clear, and thus an in-depth study is needed in the future, but a Sm-rich second phase can definitely lower the SME of the alloy.”— they concluded.
Featured image: Metallographic photo of Cu-13.0Al-4.0Ni-xSm (x = 0.2 (a), 0.5 (b)) alloys and SEM micrograph ofbCu-13.0Al-4.0Ni-xSm (x = 0.2 (c), 0.5 (d)) alloys, the illustration in (c,d) is a partial enlarged view of the box part © authors
Reference: Zhang, Q.; Cui, B.; Sun, B.; Zhang, X.; Dong, Z.; Liu, Q.; Cui, T. Effect of Sm Doping on the Microstructure, Mechanical Properties and Shape Memory Effect of Cu-13.0Al-4.0Ni Alloy. Materials 2021, 14, 4007. https://doi.org/10.3390/ma14144007
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