(Mg66.2Zn28.8Ca5)100-xCux(at%,x = 0,1,3,and 5) bulk metallic glasses(BMGs) of 2 mm in diameter were prepared by the conventional copper mold injection casting method.Besides,the influence of Cu content on the microstructure,thermal stability,mechanical properties,and corrosion behavior of Mg-Zn-Ca BMGs was investigated.It is found that the addition of Cu decreases the glass-forming ability of Mg-Zn-Ca BMGs.Crystalline phases are precipitated at a higher Cu content,larger than 3at%.The compressive fracture strength of Mg-Zn-Ca BMGs is enhanced by the addition of Cu.With the formation of in-situ composites,the compressive strength of the Mg-Zn-Ca alloy with 3at% Cu reaches 979 MPa,which is the highest strength among the Mg-Zn-Ca alloys.Furthermore,the addition of Cu also results in the increase of corrosion potential and the decrease of corrosion current density in Mg-Zn-Ca BMGs,thereby delaying their biodegradability.
Refractory high-entropy alloys present attractive mechanical properties,i.e.,high yield strength and fracture toughness,making them potential candidates for structural applications.Understandings of atomic and electronic interactions are important to reveal the origins for the formation of high-entropy alloys and their structure−dominated mechanical properties,thus enabling the development of a predictive approach for rapidly designing advanced materials.Here,we report the atomic and electronic basis for the valence−electron-concentration-categorized principles and the observed serration behavior in high-entropy alloys and highentropy metallic glass,including MoNbTaW,MoNbVW,MoTaVW,HfNbTiZr,and Vitreloy-1 MG(Zr_(41)Ti_(14)Cu_(12.5)Ni_(10)Be_(22.5)).We find that the yield strengths of high-entropy alloys and high-entropy metallic glass are a power-law function of the electron-work function,which is dominated by local atomic arrangements.Further,a reliance on the bonding-charge density provides a groundbreaking insight into the nature of loosely bonded spots in materials.The presence of strongly bonded clusters and weakly bonded glue atoms imply a serrated deformation of high-entropy alloys,resulting in intermittent avalanches of defects movement.
William Yi WangShun Li ShangYi WangFengbo HanKristopher A.DarlingYidong WuXie XieOleg N.SenkovJinshan LiXi Dong HuiKarin A.DahmenPeter K.LiawLaszlo J.KecskesZi-Kui Liu
In this work,we develop a new many-body potential for alpha-hafnium(α-Hf)based on the second moment approximation of tight-binding(TB-SMA)theory by introducing an additional Heaviside step function into the potential model and a new analytical scheme of density function.All the parameters of the new potential have been systematically evaluated by fitting to ground-state properties including cohesive energy,lattice constants,elastic constants,vacancy formation energy,structure stability and equation of state.By using the present model,the melting point,melt heat,thermal expansion coefficient,point defects,and low-index surface energies ofα-Hf were calculated through molecular dynamics simulations.Comparing with experiment observations from others,it is shown that these properties can be reproduced reasonably by the present model,some results being more consistent to the experimental data than those by previous suggested models.This indicates that this work is sutiable in TB-SMA potential for hexagonal close packed metals.
LIN DeYeWANG YiSHANG ShunLiLU ZhaoPingLIU ZiKuiHUI XiDong
(Zr41.2Ti13.8Cu12.5Ni10Be22.5 )100xNbx(at%, x=0 and 8) bulk metallic glasses (BMGs) were coated on the surface of Q195 steel wires by a continuous coating process. The potentiodynamic polarization tests of these BMGs were conducted in 3.5wt% NaCl aqueous solution. It is found that the addition of 8at% Nb into Zr 41.2Ti13.8Cu12.5Ni10Be22.5 alloy results in the improvement of corrosion resistance with the pitting potential of -52mV, the open circuit potential of -446mV, and the corrosion current density of 9.86×10 6 mA/cm2 . This may be attributed to that Nb is beneficial to passivate and stabilize Zr and Ti.
Four Zr–Cu–Fe–Al-based bulk metallic glasses(BMGs) with Zr contents greater than 65at% and minor additions of Nb were designed and prepared. The glass forming abilities, thermal stabilities, mechanical properties, and corrosion resistance properties of the prepared BMGs were investigated. These BMGs exhibit moderate glass forming abilities along with superior fracture and yield strengths compared to previously reported Zr–Cu–Fe–Al BMGs. Specifically, the addition of Nb into this quaternary system remarkably increases the plastic strain to 27.5%, which is related to the high Poisson's ratio and low Young's and shear moduli. The Nb-bearing BMGs also exhibit a lower corrosion current density by about one order of magnitude and a wider passive region than 316 L steel in phosphate buffer solution(PBS, pH 7.4). The combination of the optimized composition with high deformation ability, low Young's modulus, and excellent corrosion resistance properties indicates that this kind of BMG is promising for biomedical applications.
