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[en] The sensitivity of the mode I/III dynamic notch toughness to the loading rate was studied based on the single edge notched-three point bending test for Zr41.2Ti13.8Cu10Ni12.5Be22.5 (Vit 1) BMG. Different from a mode I fracture, a disordered vein-like pattern was found in the fracture surface under the mode I/III condition, indicating the existence of a complex stress state. It is thought that the complex stress state can promote the generation of denser shear bands. Quantitative analysis revealed that with an increasing loading rate, the shear band number (N s) increased and the spacing between the primary shear bands (λ) decreased. A power law relationship, was noted with and N s, which was similar for various BMGs under the quasi-static loading condition, and λ also showed an excellent power law correlation, with The shear band might act as a bridge between the dynamic notch toughness and loading rate. Moreover, based on the theory of self-organized criticality (SOC), additional shear bands and a smaller spacing between the primary shear bands enhance the interactions of the shear bands, which can buffer large changes, resulting in an effect on the dynamic notch toughness. (paper)
[en] Based on dynamic three-point bending tests, the dynamic notch toughness () of Zr41.2Ti13.8Cu10Ni12.5Be22.5 (Vit 1) bulk metallic glass (BMG) was found to be sensitive to stress intensity factor rate (), which varied from 5.21 to 31.90 MPa m1/2. The number of shear bands (Ns) in the notch tip plastic zone was quantitatively analyzed. The phenomenon wherein Ns decreased with increasing loading rate was explained based on the theory of the shear transformation zone and the softening mechanism. Then, power law relationships were established among Ns, and . The results showed that shear bands can affect and and act as a bridge connecting and . The sensitivity of to in BMGs can be well explained by the variation of Ns with loading rate.
[en] Highlights: • Serration directions change from upward to downward with increasing temperatures. • Decrease of the critical strain for serrations was modeled by an instability theory. • Strain bursts are caused by the combination of sample and platen of the machine. • L12 particles may act as obstacles of mobile dislocations, resulting in serrations.
[en] Highlights: • The AlCrCuFeNi2 HEA consisted of BCC solid solution and FCC solid solution. • The indentation hardness of the BCC crystals is larger than the FCC crystals. • The contact modulus of the FCC crystals is larger than the BCC crystals. - Abstract: High-entropy alloys (HEA) are multicomponent alloys with lattice structures, which have unique mechanical properties. Using X-ray diffraction, the structure of as cast AlCrCuFeNi2 HEA was characterized. The AlCrCuFeNi2 HEA consisted of body centered-cubic (BCC) solid solution and face centered-cubic (FCC) solid solution. Nanoindentation was used to characterize the indentation deformation of the FCC and BCC crystals in the AlCrCuFeNi2 HEA. Both the indentation hardness and the contact modulus of the FCC and BCC crystals decreased slightly with the increase in the indentation load and became constant for large indentation loads. For the indentation load larger than 500 μN, the contact modulus and the indentation hardness of the BCC crystals are 146 and 4.6 GPa, respectively, and the contact modulus and the indentation hardness of the FCC crystals are 207 and 2.8 GPa, respectively. The plastic energy dissipated in the nanoindentation increased with the indentation load and was proportional to the 1.77 and 1.88 power of the indentation load for the FCC and BCC crystals, respectively. The ratio of the dissipated plastic energy to the total energy in the indentations was a linear function of the ratio of the residual indentation depth to the corresponding maximum indentation depth. The slope of the energy ratio verse the indentation depth ratio for the BCC crystals is larger than that for the FCC crystals
[en] The structures of liquid Fe–C alloys in the Fe-rich end were investigated by ab initio molecular dynamics simulations. The trend of intensity of chemical short range order around Fe and C atoms changes at the eutectic composition, indicating the close correlation between liquid structure and phase diagram. The tri-capped trigonal prism (Voronoi index <0,3,6,0>) and mono-capped square archimedean antiprism (Voronoi index <0,4,4,0>) around C atoms have the largest frequency fractions and the longest lifetimes among all the polyhedra. Moreover, they tend to connect with each other to form network structure. The maximum intensity of network structure is located at the 20% C composition, which might be the reason why alloys near eutectic composition have great glass-forming ability. - Highlights: • A new parameter is proposed to describe chemical short range order. • Close correlation between structure and phase diagram is found in Fe–C system. • Close correlation between structure and glass forming ability is also found
[en] Highlights: • Wear rate of nitrided HEAs was lower than that of as-cast HEAs in the same condition. • The wear mechanism of as-cast alloys in air was abrasive wear of oxide particles. • The wear mechanism of the nitrided HEAs in air was adhesive wear and abrasive wear. • The wear mechanism of HEAs in acid rain was abrasive, oxidative and corrosive wear. • The lubrication action of deionized water and acid rain led to the lower wear rate.