Effect Of Atomic Bond Proportion And Free Volume On The Properties Of Metallic Glasses

Identifying the underlying mechanisms of the special physical properties of metallicglasses (MGs) is of fundamental interest. The complexity and uncertainty in the structureof MGs have been an obstacle to the development of an efficient structure-propertyrelationship. To predict the properties of MGs, this work presents atomic bondproportion and free volume content, instead of exploring the complicated atomicstructure. Atomic bond proportion is a totally new parameter which can be calculatedthrough partial coordination number method and statistical calculations method. Partialcoordination number method can calculate the atomic bond proportion by the averagepartial coordination number of the MGs. This method can be easily acceptable but thepartial coordination number is hard to obtain. Statistical calculations method can directlycalculate the atomic bond proportion through component mole fraction and atomic radius.This method has a wide application, but it can only be applied to the MGs with metallicbond. Based on these two methods, the proportion of different types of atomic bonds fora series of MGs (e.g., Ca60Mg15Zn25, Zr67Ni33, and Al90Y10) is successfully given, and theresults from both methods significantly agree with each other.The present letter studied the influence of the preparation of MGs and commonprocessing methods on atomic bond proportion and free volume content, respectively. Itcan be found that the initial temperature of the quenching and the cooling rate greatlyinfluent the free volume content, but they have little influence on the atomic bondproportion. High pressure treatment is conducive to the annihilation of the free volumeand plastic deformation is beneficial to the formation of free volume. Meanwhile, highpressure makes it easier for the smaller atoms to squeeze into the interstice between thebigger atoms, which increases the atomic bond number between the heterogeneous atoms,but decreases the atomic bond number between the similar atoms. Therefore, for theMGs with small component atomic sizes difference, high pressure can hardly haveinfluence on the atomic bond proportion. However, for those rare earth-based MGswhose component atomic sizes are of large difference, the atomic bond proportionexperiences a significant variation. The previous studies have achieved remarkable results in estimating the elasticitymodulus by carrying out weighted average on elasticity modulus of fine metal, that is,Mf iMi. Statistical calculations method establishes the relationship between thecomponent and the atomic bond proportion. The macroscopical properties of the materialis determined by the atomic interaction, and there’s no exception with the MGs. Takingthe atomic bond as the component and employing the weighted average method, thepresent work studies the various macroscopical properties of MGs. This newcombined-method can explain some unexplained problems. Taking Zr-Cu alloy as theexample, elasticity modulus does not monotonously rise with the increase of the contentof Cu. Due to large negative mixing enthalpy, the strength of Zr-Cu bond is more greaterthan Zr-Zr bond and Cu-Cu bond. The application of the new combined-method canaccurately fit the curve between elasticity modulus and component. Meanwhile, it alsoobtains significant achievement in studying crystallization temperature and enthalpy offormation of MGs system. The present letter calculates the multi-system enthalpy ofmixing which is from the heterogeneously atomic interaction by making use ofheterogeneously atomic bond proportion, the results of which is consistent with that ofthe previous studies.During the rapid cooling process, the atomic motion becomes locked in a short time.Being lack of sufficient relaxation, large number of free volume is residual. The contentof free volume reflects the degree of density of MGs and greater free volume decreasesthe mechanical property and chemical property of materials and the stability of theamorphous phase. The present letter annihilates large number of free volume by highpressure treatment, in which way many properties can be remarkable improved.