Wetting Behaviors And Interfacial Characteristics Of TiZr-based BMG Melt And TiZrCu Alloy

Recently,the glass forming ability?GFA?of Ti-based metallic glass have been improved to centimeter level,Ti-based bulk metallic glasses?BMG?are of great industrial structure application due to their high strength and low density.However,the very little plastic deformation at room temperature limit the wide application of BMG.By the addition of the second phase,preparing the bulk metallic glass composites?BMGCs?,the plasticity of BMG can be effectively improved.Currently,some reports take attention tothe controllable structure of BMGCs,which is of great significant to develop BMGCs with good performance.The preparation of ex-situ BMGCs is simple and controllable,the two phases of in-situ BMGCs usually have good consistency and quality of interface bonding.In this thesis,based on the wettability of matrix and the second phase,the feasibility of prepare the Ti32.8Zr30.2Ni5.3Cu9Be22.7/Ti_61.5Zr_36.4Cu_2.1 laminar BMGCs and its microstructure are studied,which the Ti_61.5Zr_36.4Cu_2.1 have excellent consistency with Ti32.8Zr30.2Ni5.3Cu9Be22.7.The wetting behavior of Ti32.8Zr30.2Ni5.3Cu9Be22.7melt on Ti_61.5Zr_36.4Cu_2.1 substrate have been studied,the melt wets the substrate well.The decrease of contact angle can be divided into two stages under continuous heating.The wetting kinetics shows two stages of rapid spreading and equilibrium under isothermal condition?750,800 and 850??.The dissolution of Ti_61.5Zr_36.4Cu_2.1 substrate occurred at the interface,and the solid / liquid junction form a diffusion layer which indicates the good quality of connection.After the melting of Ti32.8Zr30.2Ni5.3Cu9Be22.7,the primary crystallization product precipitate,and this product completely disappear until 800?.So,to prepare this BMGC,the holding temperature should be controlled over 800?.To study the microstructure of the laminar BMGCs,liquid-bridge specimens which simulates the laminated connection of Ti32.8Zr30.2Ni5.3Cu9Be22.7/Ti_61.5Zr_36.4Cu_2.1 laminar BMGCsare prepared by water quenching method.The results show that the laminar BMGCs is consisted of in-situ dendrites BMGCs layer and the remaining Ti_61.5Zr_36.4Cu_2.1 alloy layer after dissolution.Based on good componential stability of Ti_61.5Zr_36.4Cu_2.1 and Ti32.8Zr30.2Ni5.3Cu9Be22.7,the BMGCs layer is consisted of Ti32.8Zr30.2Ni5.3Cu9Be22.7 metallic glass matrix and ?-Ti?Zr,Cu?dendrites.Under a certain cooling rate,Ti_61.5Zr_36.4Cu_2.1 have solubility inTi32.8Zr30.2Ni5.3Cu9Be22.7melt,the concentration of Ti_61.5Zr_36.4Cu_2.1 in the melt must over the solubility,so can the dendrites precipitate.With the prolonging of holding time,the dendrites are well-distributed in the BMGCs layer.Measuring the dissolution depths of liquid-bridge substrates,due to the lower density of Ti_61.5Zr_36.4Cu_2.1 compare to Ti32.8Zr30.2Ni5.3Cu9Be22.7melt,the dissolution depth of the lower substrate is higher than that of the upper side,influenced by gravity driven convection.A prediction model is chosen to fit the dissolution depth of the substrate,and the correctness of the fitting value is verified.According to the fitting value,we can understand the fraction of the well-distributed dendrites under different temperatures,so as to control the performance of the BMGCs layer.In addition,the model can also be used to design the layer thickness ratioto control the performance of the laminar BMGCs.