Serrated flows are known as repeated yielding of bulk metallic glasses（BMGs）during plastic deformation under different loading conditions,which are associated with the operation of shear banding.According to the statistics of some parameters,the shear avalanches can display a self-organized critical state,suggesting a large ductility of BMGs.The emergence of the self-organized criticality（SOC）behavior in different BMGs is due to the temperature,strain rate,and chemical compositions.The SOC behavior is accompanied with the following phenomena：the interactions occur in the shear bands;the incubation time is longer than the relaxation time;the time interval is lacking of typical time scale;and the spatial or temporal parameters should display apower-law distribution.
The metallic glass matrix composites（MGMCs）and bulk metallic glasses（BMGs）were studied by statistical analysis during plastic deformation at the strain rates of 2×10^-2,2×10^-3,and 2×10^-4 s^-1,respectively.No serration events occur in both MGMCs and BMGs during compression tests at the strain rate of 2×10^-2 s^-1.When deformed at the strain rate of 2×10^-3 s^-1,the BMG displays a larger plasticity,which is due to the larger serration events followed by a series of small serrations caused by the continuous movement of free volume.The amplitudes and elastic-energy densities increase with increasing the strain rates owing to many serrations in MGMCs.It is deduced that the Young′s modulus decreases from the normalized stress drop and fluctuations are observed on stressstrain curves,which is attributed to a lower coefficient according to the stick-slip model.
Zhong WANGJiao-jiao LILi-wei RENYong ZHANGJun-wei QIAOBao-cheng WANG
The tribological properties of the in-situ dendrite-reinforced metallic glass matrix composite（Ti42Zr22V14-Cu5Be17）prepared by copper mould casting were analyzed at different normal loads under the dry condition and rainwater.The results showed that the average value of the frictional coefficients and micro-hardness ascended with increasing the normal load,while the wear rate showed a trend of decline under the dry condition.The electrochemical test results showed that the surface of samples was pitting corroded in the rainwater.The matrices were corroded first.Then the dendrites were exposed,leading to the damage of the surface.Both the frictional coefficients and wear rate of the composite in the rainwater were larger than those under the dry condition,primarily owing to the corrosion of chloride ions on the worn surface.The wear mechanisms of composites were mainly adhesive wear,accompanied by the abrasive wear under the dry condition and corrosive wear in the rainwater.The composites have higher wear resistance both under the dry condition and rainwater due to the lower wear rate.
Teng ZHANGXiao-min LINHui-jun YANGYong LIUYong-sheng WANGJun-wei QIAO
Multicomponent alloys with high entropy of mixing,e.g.,high entropy alloys（HEAs）and/or multiprincipal-element alloys（MEAs）,are attracting increasing attentions,because the materials with novel properties are being developed,based on the design strategy of the equiatomic ratio,multicomponent,and high entropy of mixing in their liquid or random solution state.Recently,HEAs with the ultrahigh strength and fracture toughness,excellent magnetic properties,high fatigue,wear and corrosion resistance,great phase stability/high resistance to heat-softening behavior,sluggish diffusion effects,and potential superconductivity,etc.,were developed.The HEAs can even have very high irradiation resistance and may have some self-healing effects,and can potentially be used as the first wall and nuclear fuel cladding materials.Serration behaviors and flow units are powerful methods to understand the plastic deformation or fracture of materials.The methods have been successfully used to study the plasticity of amorphous alloys（also bulk metallic glasses,BMGs）.The flow units are proposed as：free volumes,shear transition zones（STZs）,tension-transition zones（TTZs）,liquid-like regions,soft regions or soft spots,etc.The flow units in the crystalline alloys are usually dislocations,which may interact with the solute atoms,interstitial types,or substitution types.Moreover,the flow units often change with the testing temperatures and loading strain rates,e.g.,at the low temperature and high strain rate,plastic deformation will be carried out by the flow unit of twinning,and at high temperatures,the grain boundary will be the weak area,and play as the flow unit.The serration shapes are related to the types of flow units,and the serration behavior can be analyzed using the power law and modified power law.
