Mechanical Properties,Damage and Fracture Mechanisms of Bulk Metallic Glass Materials

The deformation, damage, fracture, plasticity and melting phenomenon induced by shear fracture were investigated and summarized for Zr-, Cu-, Ti- and Mg-based bulk metallic glasses （BMGs） and their composites. The shear fracture angles of these BMG materials often display obvious differences under compression and tension, and follow either the Mohr-Coulomb criterion or the unified tensile fracture criterion. The compressive plasticity of the composites is always higher than the tensile plasticity, leading to a significant inconsistency. The enhanced plasticity of BMG composites containing ductile dendrites compared to monolithic glasses strongly depends on the details of the microstructure of the composites. A deformation and damage mechanism of pseudo-plasticity, related to local cracking, is proposed to explain the inconsistency of plastic deformation under tension and compression. Besides, significant melting on the shear fracture surfaces was observed. It is suggested that melting is a common phenomenon in these materials with high strength and high elastic energy, as it is typical for BMGs and their composites failing under shear fracture. The melting mechanism can be explained by a combined effect of a significant temperature rise in the shear bands and the instantaneous release of the large amount of elastic energy stored in the material.

Moiré-superlattice MXenes enabled ultra-stable K-ion storage in neutral electrolyte

Ti_(3)C_(2)MXene is an auspicious energy storage material due to its metallic conductivity and layered assembly.However,in the real working condition of electrochemical energy storage with long cycle charging-discharging,a structural collapse is usually caused by the stacking of its layers creating a large attenuation of specific capacitance.Inspired by the superlattice effect of magic angle graphene,we conducted microscopical regulation of rotation mismatch on the Ti_(3)C_(2)lattice;consequently,a hexagonal fewlayered Ti_(3)C_(2)free-standing film constructed with Moiré-superlattices.Such finding not only solves the problem of Ti_(3)C_(2)structural collapse but also dramatically improves the specific capacitance of Ti_(3)C_(2)as a supercapacitor electrode under long cycle charging and discharging.The ultra-stable energy storage of this electrode material in a neutral aqueous electrolyte was realized.Moreover,the formation mechanism of rotating Moirépattern is revealed through microscopy and microanalysis of the produced Moirépattern,assisted with modeling and analyzing the underlying mechanism between the Moirépattern and the rotation angle.Our work provides experimental and theoretical support for future construction of Moiré-superlattice structure for a wide range of MXene phases and is undoubtedly promoting the development of MXene materials in the field of energy storage.

Microstructure and mechanical properties of Fe_xCoCrNiMn high-entropy alloys

The microstructure and tensile properties of FexCo Cr Ni Mn high-entropy alloys(HEAs) were investigated.It was found that the FexCo Cr Ni Mn HEA has a single face-centered cubic(fcc) structure in a wide range of Fe content. Further increasing the Fe content endowed the FexCo Cr Ni Mn alloys with an fcc/bodycentered cubic(bcc) dual-phase structure. The yield strength of the FexCo Cr Ni Mn HEAs slightly decreased with the increase of Fe content. An excellent combination of strength and ductility was achieved in the FexCo Cr Ni Mn HEA with higher Fe content, which can be attributed to the outstanding deformation coordination capability of the fcc/bcc dual phase structure.