Trends and Advances in Nano-structured Materials with Novel Structures and Properties

In this work, AlCo_xCrFeNi_3.1–x (x = 0.4, 1) high-entropy alloys (HEAs) were investigated. The effects of different Co and Ni content (both of which are FCC stabilizers with similar atomic radii) on the microstructure and mechanical properties of the system were studied with the goal of improving the cost-effectiveness of the alloys. AlCo₀⋅₄CrFeNi₂⋅₇ and AlCoCrFeNi₂⋅₁ were prepared via vacuum induction melting. X-ray diffraction and scanning electron microscope results demonstrated that an FCC+B2 structure formed. Additionally, tensile tests at room temperature and impact tests at 77, 200, and 298 K were also carried out. From the results, it could be determined that the tensile properties of the tested samples were similar. The impact toughness of AlCo₀⋅₄CrFeNi₂⋅₇ with a V-notch was 21.77 J at 298 K, and this was more than three times larger than that of AlCoCrFeNi₂⋅₁. Compared with the Al₀⋅₃CoCrFeNi and Al₀⋅₁CoCrFeNi FCC structured HEAs, AlCo_xCrFeNi_3.1–x alloys showed low impact toughness but had a high yield strength.

A composite high manganese structure comprising recovered and recrystallized structures was prepared using a single-phase austenitic Fe-30Mn-0.14C-7Cr-0.26Ni steel by cold rolling and annealing. The yield strength and elongation of the composite increased simultaneously, when the tensile temperature decreased from room temperature (RT) to low temperature (−180°C). The composite structure exhibited a good combination of strength and ductility at RT and −180°C. The notable mechanical properties at low temperature can be attributed to the enhanced strain-hardening capability via introducing multiple deformation mechanisms in the composite structure.