Effect Of Cryogenic Treatment On Microstructure And Mechanical Properties Of Ti Based Bulk Amorphous Composites Ti₄₈Zr₁₈V₁₂Cu₅Be₁₇

Bulk-metallic glasses?BMGs?have become the focus of researchers because of their excellent mechanical properties,such as high fracture strength and up to 2%elastic strain limit.But during the compression deformation at room temperature,brittle fracture occurs due to the rapid expansion of the single shear band.Then,in order to solve this problem,the amorphous composite materials with the addition of particle and endogenous dendrite are developed.In the process of deformation,the plasticity of amorphous composite materials is improved due to the second phase can effectively impede the expansion of a single shear band and form multiple shear bands.In this paper,the amorphous composite Ti₄₈Zr₁₈V₁₂Cu₅Be₁₇ was prepared by high vacuum arc melting and copper die casting.The microstructures of the cast and cyclic cryogenic specimens were studied by using optical microscopy?OM?,scanning electron microscopy?SEM?,energy dispersive spectrometer?EDS?,X ray diffractometer?XRD?and transmission electron microscopy?TEM?.The properties of Amorphous Composites before and after cyclic cryogenic cooling were studied by means of Vivtorinox hardness,differential scanning calorimetry?DSC?and room temperature compression.Firstly,the microstructure and mechanical properties of the top and the end of the as-cast samples were studied respectively.The results show that the size of the dendritic phase at the top and end of the cast sample first increased and then decreased from the edge to the center,which is extremely uneven,the grain size in the middle region is the largest that the grain size grade is No.12 and No.9 respectively.The average grain grade of the top and the end are No.12¹3 and No.10¹1,respectively.The result of XRD shows that the dendritic phase is?-Ti that the lattice constant is a=b=c=0.328nm,and the results of the projective electron microscope?TEM?are in agreement with the results of XRD.The static compression test results show that the maximum yield strength and plastic strain of the as cast sample are 2016MPa and 10.91%respectively,and the fracture mode is mainly plastic fracture.The ANSYS simulation software is used to simulate the temperature field and the velocity field of the casting process.The results show that the evolution of the inhomogeneous microstructure is determined by the larger temperature gradient from the edge to the center and the growth law of the free crystal during the filling process,which makes the grain size of the middle region the largest.Secondly,the microstructure and mechanical properties of Amorphous Composites after cyclic cryogenic treatment were analyzed.The results showe that the morphology and size of the dendritic phase were not changed,which indicats that the Ti-base amorphous was more stable.Through the analysis of SEM and EDS,there was internal stress in the deep cold state,but no new nanocrystalline precipitation was found.With the increase of the cycle times,both the hardness and the fracture strength increase,and the maximum value 499.38Hv and 2175MPa are reached at 8 cycles,but the plasticity does not show a certain regularity.