Search

The effects of casting and different heat treatment processes on the corrosion resistance of AlFeCoNiMo0.2 high-entropy alloy in 3.5% NaCl (mass fraction) and 0.5 mol/L H2SO4 solutions were investigated using dynamic potential polarization curves, SEM, XRD, XPS, and other test methods. The results show that in the Cl− environment, the cast alloy has the lowest corrosion current density and higher corrosion resistance compared to the annealed alloy. The elements Al and Mo are severely segregated in the crystal and in the grain boundaries, where galvanic corrosion occurs, and the Al-rich phase produces pitting corrosion in the crystal. The main components of its passive film are oxides of Al, Fe, Co, and Mo, and oxides and hydroxides of Ni. In the SO42− environment, the best corrosion resistance is achieved in the 900 °C annealed state of the alloy. Electrochemical test results show that the alloys all undergo secondary passivation, producing two successive product films to protect the metal matrix. Preferential corrosion areas are concentrated in the molybdenum-rich grain boundaries and nearby dendritic regions, reducing the corrosion resistance of the alloy. The main components of the passive film are oxides of Al and Mo; oxides of Fe, Co, Ni; and hydroxides. The Mo element in the passive film prevents the activated dissolution of Fe and produces the protective component MoO3, which inhibits the dissolution of the alloy and improves the stability of the passive film. The presence of Mo elements increases the selective dissolution of Fe, and the aggregation of Mo elements at grain boundaries after annealing weakens the corrosion resistance of the alloy and leads to the dissolution of the passive film. The main components of the passive film are oxides of Al and Mo; oxides of Fe, Co, Ni; and hydroxides.

As an efficient hydrogen storage material, magnesium hydride (MgH2) has a high capacity of 7.6 wt%. However, its performance deteriorates because of high thermodynamic and kinetic temperatures and the fast agglomeration of its nanocrystals during the hydrogen uptake and release process. The exploration of efficient catalysts is a popular, but currently challenging, topic. Therefore, we successfully prepared flake-like molybdenum (Mo) catalysts and doped them into MgH2 to enhance its properties. We found that the incorporation of 7wt%Mo into MgH2 could reduce the starting desorption temperature by approximately 100 °C. In addition, the 7wt%Mo-doped MgH2 could desorb almost all of the H2 within 20 min at a 325 °C isothermal condition. For hydrogenation, MgH2-7wt%Mo could absorb approximately 5 wt% of hydrogen within 5 min at a 250 °C isothermal condition with a hydrogen pressure of 3 MPa. In addition, the MgH2-7wt%Mo composite could maintain approximately 98% of the initial capacity at the end of 22 cycles, presenting good cycling performance.

The cyclic stress response behavior of Ti-3Al-8V-6Cr-4Mo-4Zr alloy with three different microstructures has been systematically studied. The cyclic stress response was highly related to the applied strain amplitude and precipitated phase. At low strain amplitude, the plastic deformation was mainly restricted to soft α phase, and a significant cyclic saturation stage was shown until fracture for all three alloys. At high strain amplitude, three alloys all displayed an initial striking cyclic softening. However, the softening mechanism was obviously difference. Interestingly, a significant cyclic saturation stage was noticed after an initial cyclic softening for alloy aging for 12 h, which could be attributed to the deformation of {332} twin and precipitation of α″ martensite.