Mechanical Properties and Serration Behavior of a NiCrFeCoMn High-Entropy Alloy at High Strain Rates

Serration behavior is a kind of plastic instability phenomenon of materials, which widely exists in the high-entropy alloys and has influence on microstructure and mechanical properties. In this work, the microstructure and mechanical properties of a NiCrFeCoMn high-entropy alloy (HEA) were studied under high-speed impact. The microstructure of a NiCrFeCoMn HEA were investigated by optical microscope (OM), scanning electron microscope (SEM), electron backscatter diffraction (EBSD), and transmission electron microscope (TEM). The dislocation density increased with the true strain at high-strain-rate deformation, and the dislocations can be hindered and released continually by the twin layers, resulting in serration on the true stress—true strain curve. When values of the strain rates are 1250, 2000 and 4800 s−1, the yield strength of the deformed NiCrFeCoMn HEA are 510, 525 and 680 MPa, respectively. Moreover, the fluctuation of the serration became more serious with the increasing of the strain rate. Compared with the as-cast NiCrFeCoMn HEA, the true stress—true strain curve of the deformed NiCrFeCoMn HEAwas smoother.

Effects of Si Addition on Microstructure, Properties and Serration Behaviors of Lightweight Al-Mg-Zn-Cu Medium-entropy Alloys

A series of as-cast lightweight multicomponent alloys Al(86-x)Mg10Zn2Cu2Six (x=0, 0.3, 0.6, 0.9, 1.2 at.%) were prepared by a vacuum induction furnace with a steel die. With the addition of Si, the reticular white Al-Cu phase deposited were gradually replaced by the gray eutectic Mg-Si phase, while the compressive strength of the alloys increases first and then decreases slowly. It is particularly noteworthy that the compression plasticity also exhibits this trend. When the Si content is 0.9 at.%, the compressive strength reaches its maximum at 779.11 MPa and the compressive plasticity reaches 20.91%. The effect of the addition of Si on the serration behavior of alloy was also studied; we found that the addition of Si introduces a new MgSi phase, and with the change of Si is significantly affects the morphology of the precipitated phase, which affects the serration behavior of the alloys. The comprehensive mechanical properties of the alloy are optimal at the critical point where the serration behavior disappears. In this work, we have provided a method and a composition for the preparation of a low-cost, high-strength, lightweight medium-entropy alloys.