Research About The Solidification Behavior Of TiZr-based In Situ Bulk Metallic Glass Matrix Composites

The in situ BMGMCs stand out for their perfect combinations of mechanical properties?such as high strength and well plastic deformation?and better ability of interface adhesive.Thus,based on the excellent properties,the in situ BMGMCs have a wide prospect of engineering application.In this thesis,a systematic study has been performed on a series of in-situ bulk-metallic-glass-matrix composite?BMGMC?with nominal compositions of?Ti₆1.5Zr₃6.4Cu₂.1?x?Ti₃2.8Zr₃0.2Ni₅.3Cu₉Be₂2.7?100-x?x=10,20,30,40??denoted as 10B,20B,30B,40B?.And the influences of the constituent of alloy composites and cooling rates also have been investigated on the microstructures,thermal stability and mechanical properties of TiZr-based in situ BMGMCs.Through the study about the microstructures of the samples of TiZr-based in situ BMGMCs that under different cooling rate,we gain the schematic diagram for the constituent of alloy composites-cooling rate-microstructures of in situ BMGMCs.It denotes that when samples that has a low molar percent of crystalline phase and be produced under low cooling rate,the microstructures of sample is made up of amorphous and icosahedral quasicrystalline phase.And with the increase of the molar percent of crystalline phase and cooling rate,the microstructures of the samples turned from pure bulk metallic glass to the mix structures of bulk metallic glass and dendrites.Through the study of thermal analysis,it is found that at a heating rate of 20K/min,with the increase of the molar percent of crystalline phase,the order of the quasicrystalline in the amorphous melt increase,leading to the amount of quench-in nuclei arise and causing the inhomogeneous nucleation during the process of heating.Thus it will reduce the thermal stability of TiZr-based in situ BMGMCs.By the time the precipitation of crystalline,the summit of pre-Tg appears on the curve of DSC and the temperature of the first crystallization peak will become higher,thus enhancing the thermal stability of samples.The constituent of alloy composites and the cooling rate have a significant influence on the mechanical properties.Basically under the experimental cooling rate,when the amount of Ti₆1.5Zr₃6.4Cu₂.1 is small,and the microstructure of alloy is pure amorphous or the percent of the amorphous is high,the samples belongs to brittle fracture.When the amount of Ti₆1.5Zr₃6.4Cu₂.1 is large,the precipitation of crystalline also increases.Thus the samples perform well comprehensive mechanical properties,not only have a high compressive strength,but also own well ability of plastic deformation.