Shear Stability And Strengthening Of Metallic Glasses

As a new type of amorphous material,the internal atomic distribution of metallic glasses,（MGs）is disordered,featuring long-range disorder and short-range order,which is completely different from traditional crystalline alloys.Therefore,compared with tra-ditional alloys,metallic glasses have a series of excellent properties,such as high strength,high elasticity,excellent soft magnetic properties,and good catalytic properties,etc..Among them,the mechanical properties are particularly outstanding and have become a hot research topic in the field of metallic glasses.Due to its unique disordered structure,the plastic deformation of metallic glasses is highly concentrated in the shear band at the nano-meter scale.The unstable expansion of the shear bands leads to catastrophic fracture of metallic glasses,which greatly limits the application of metallic glasses in the field of structural materials.Room temperature brittleness and unstable catastrophic fracture of metallic glasses has become a pressing problem in the field of metallic glasses.In this paper,the effect of external factors such as temperature on the shear stability of metallic glasses is investigated to address the problem of unstable fracture at room temperature,and various strategies are used to improve the shear stability of metallic glasses and strengthening metallic glasses.We investigate the plastic deformation behaviour of Zr-based metallic glasses at different temperatures and find that the plasticity of Zr-based metallic glasses does not vary monotonically with temperature,but has an maximum value at a certain temper-ature.The maximum value of plasticity of Zr-based metallic glasses corresponds to the transition point from serrated flow to non-serrated flow.Furthermore,by studying the serration events on the stress-time curves,we find shear bands slide steadily at a constant rate at the transition point,shear bands are most stable and the shear stability of metallic glasses is very high.The results show that Zr-based metallic glasses have the best shear stability at the transition point from serrated flow to serrated flow,which deepens the understanding of the shear band kinetic behaviour and macroscopic plasticity of metal-lic glasses and provides a theoretical basis for the design of metallic glasses for low temperature plasticity.We studies the plastic deformation behaviour of Ir-Ni-Ta high-temperature metallic glasses at the micro-nano scale and found that brittle Ir-Ni-Ta high-temperature metallic glasses have extraordinary intrinsic shear stability at the micro-nano scale.The experi-mental results show that the brittle fracture of Ir-Ni-Ta high-temperature bulk metallic glass occurs before reaching the yield point,while the plastic deformation of Ir-Ni-Ta high-temperature metallic glass changes from brittle fracture to serrated flow with ex-traordinary intrinsic shear stability when the sample size is reduced to the micro-nano scale.Ir-Ni-Ta high temperature metallic glass micropillars with diameters ranging from～500 nm to～5μm all exhibit plasticity in excess of 25%up to 35%and yield strength can reach 7 GPa,far exceeding the strength of most metallic materials.Furthermore,we calculated the shear band slip distances for different systems of metallic glasses in ser-ration events and normalized by the sample diameter to describe the shear stability of metallic glasses.The results show that the Ir-Ni-Ta high-temperature metallic glass has higher shear stability than Mg-,Zr-,and Cu-based metallic glasses with good deforma-bility.The results make Ir-Ni-Ta high-temperature metallic glass an ideal candidate for micro-and nano-devices operating at high temperatures or under extreme conditions.By introducing second-phase nanocrystalline in Ti-based metallic glasses,we have developed Ti-based nanocrystalline/amorphous dual-phase alloy with ultra-high yield strength and ultra-high specific strength,with yield strengths up to 3.6 GPa and specific strengths up to 704.6 N·m·g^-1,much higher than those of pure Ti,Ti alloys and Ti-based metallic glasses.During the plastic deformation of Ti-based nanocrystalline/amorphous dual-phase alloy,the nanocrystalline dispersed in the metallic glass matrix hinder the expansion of the shear band and accompany its own fragmentation,greatly reducing the degree of stress and strain localisation and improving shear stability.The small angular grain boundaries between the nanocrystalline and the large number of stacking faults prevent the sliding of dislocations in the nanocrystalline during plastic deformation and have an enhanced effect on the strength of the material.The research results promote the application of Ti alloys in the field of micro/nano-devices,and also significantly advance the development of lightweight alloy materials.In this paper,the effect of temperature on the shear stability of metallic glasses is investigated and different methods are applied to improve the shear stability of metallic glasses.Furthermore,we develop Ti-based nanocrystalline/amorphous dual-phase al-loy with ultra-high specific strength.This improves the problem that metallic glass is prone to destabilization and fracture,increases the shear stability of metallic glass,and promotes the application of metallic glass in the field of structural materials.