The Impact Of Crystallization Behavior On Bulk Metallic Glass Mechanical Properties

With the development of science and technology,more and more novel multi-component alloys with extremely good glass forming ability(GFA)are obtained. It enables the synthesis of bulk amorphous alloy at very low cooling rate.Compared to the conventional amorphous alloys,the bulk ones usually exhibit a distinct glass transition process,large supercooled liquid region and high thermal stability.Once crystallization occurs amorphous alloys will loss many good properties.In this dissertation,research activities are mainly focused on crystallization of amorphous alloys and the influence for deformation in the supercooled liquid region Zr_53.5Ni₅Cu_26.5Al₁₂Ag₃ bulk amorphous alloy is chosen in the study which exhibit good GFA and high thermal stability against crystallization in supercooled liquid region Static annealing tests and high temperature thermal compression tests combined with differential scanning calorimetry(DSC),X-ray diffraction(XRD)and microhardness analyzer are used to investigate crystallization and deformation of bulk amorphous alloy Influence of the annealing temperature and annealing time on crystallization,annealing temperature and time and strain rate on deformation are analyzed.Based on the relationship between nano-crystalline and high temperature mechanical properties of amorphous alloy,constitutive equation of flow stress,temperature,strain rate and crystallization phase volume fraction are discussed.Some of main experimental results and conclusions are listed as follows:at the same annealing temperature,the primary stage crystallization rate is small.Then it increases sharply which follow S curve.With the annealing time extend,both crystallization volume fraction and crystallization rate increased.For structure relaxation and nano-crystalline,the microhardness of annealed samples rise.The homogeneous rheological behavior of bulk amorphous alloy in supercooled liquid region depends on the temperature and strain rate.With lower temperature or increasing strain rate of rheological behavior shows that Newtonian flaw change to non-Newtonian flow.During amorphous alloy hot defomlation tests,peak stress varies in the law with the temperature,annealing time and the strain rate'S change.