Study On Deformation Mechanism Of Amorphous Alloys And Preparation Of CuZr-based Bulk Amorphous Alloys

Since the first discovery of bulk amorphous alloys,it has been favored for its excellent physical,chemical and mechanical properties.The unique properties of amorphous alloys are derived from their inherent atomic structure:short-range order and long-range disorder.However,the defect most amorphous alloys have poor room temperature plasticity or brittle greatly restricts the further development and application of such materials.Nowadays,the exploration ofthe microstructure and the mechanism of plastic flow of amorphous alloys have been the focus of attention.Although many structural models and theoretical models of plastic flow have been proposed,none of them can fully explain the mechanical,physical and chemical behavior of amorphous alloys in service.On the one hand,based on the classic BDT percolation theory and the existing theoretical model of plastic flow of amorphous alloys,a new percolation model for plastic yield with amorphous alloys as percolation system has been established,and the yield behavior of amorphous alloys is also studied microscopicallyin this paper.On the other hand,the applicability of different yield criteria in the tensile and compressive experiments of amorphous alloys is analyzed based on the macroscopic fracture characteristics of amorphous alloys under tension and compression.Moreover,some new bulk amorphous alloys have been prepared.The main contents and research results are summarized as follows:1)Firstly,the research history,properties and applications of amorphous alloys,as well as important structural models are introduced.Secondly,two important rheological phenomena and related rheological theoretical modelsof amorphous alloys and percolation theory are analyzed in detail.Finally,a new percolation model for yield of amorphous alloys has been established,and the critical phenomena for ductile-brittle transition hasalso been discussed.2)Based on free volume theory,STZ theory,flow unit theory and classical BDT percolation theory,a percolation model for plastic yield of amorphous alloys has been established.In addition,Some meaningful microstructural parameters are also proposed.3)The results show that the plastic deformation ability of amorphous alloys is related to the size and distribution of the flow unit.The smaller the size of the flowunit and the looser the distribution,the higher the plastic deformation ability of the amorphous alloys;on the contrary,the worse the plastic deformation ability of the amorphous alloys.The ductile-brittle transition mechanism of 94 kinds of amorphous alloys with different compositions in different systems was studied.It was found that the size of flow unit of amorphous alloys in the same system was influenced by the main elements in the alloy composition.It is also found that the ductile-brittle transition threshold(?SC?0.515)of amorphous alloys is similar to the critical reduced free volume x?0.024 on plastic yield,which is the inherent property of amorphous alloys..4)The tensile-compressive asymmetry of the shear fracture of amorphous alloys originates from its unique micro-atomic structure,but this unique phenomenon can be well explained by the improved Mohr-Coulomb(M-C)?Drucker-Prager(D-P)and the newly developed elliptic criterion.Comparing the predicted values calculated by the improved three criteria with the experimental values of tension and compression tests,it is found that under uniaxial compressive stress,D-P criterion is more suitable for amorphous alloy yield criterion,while under uniaxial tension stress,elliptic criterion is more suitable.5)Cu45Zr55-xAlx(x=5,6,7,8,9,and10 at.%)bulk amorphous alloys have been successfully developed,and its critical diameter is greater than or equal to 8 mm.