The Designing And Deformation Behavior Of TRIP Reinforced Bulk Metallic Glass

Bulk metallic glasses(BMGs)have attracted large attention because of their unique properties,such as high strength,large elastic limit,excellent corrosion and wear resistances,etc.However,they are known for being extremely brittle,failing in a catastrophic fracture at room temperature,due to the prompt of localized shear bands.To enhance macroscopic plasticity,metallic glass matrix composites(MGMCs)have been developed by in situ or ex situ introduction of secondary phases,which can hinder the rapid propagation of shear bands.In recent years,a series of in-situ dendrite-reinforced MGMCs have been developed,such as Ti-based and Zr-based MGMCs.But these MGMCs exhibit a macroscopic strain softening due to lack of work hardening in the glass matrix at room temperature,which limiting the applications significantly.Recently,these shortcomings have been successfully addressed in some CuZr-based MGMCs reinforced by ductile B2 CuZr phases.B2 CuZr phases can undergo a stress-induced martensitic transformation from B2 phase to a monoclinic B19? phase,which imparts an appreciable work-hardening capability and then compensates the softening of the matrix significantly during plasticflows.Accordingly,we focused on the CuZr-based MGMCs.In the present study,the effect of trace element Ni on the glass forming ability of CuZr-based MGMCs is studied.Based on this,the mechanical behavior and deformation mechanism of CuZr-based MGMCs with different volume fractions of crystalline phases at room temperature are systematically investigated.However,whether the mechanical properties of CuZr-based MGMCs at high temperature can meet the engineering application are also considered,so the rheological behavior of CuZr-based MGMCs in supercooled liquid region are studied and discussed.The main contents and conclusions are listed below:(1)The Zr48Cu48-xAl4 Nix with different volume fractions of crystalline phases were designed by doping of nickel.Minor addition of nickel element can change the glass-forming ability of the resultant composites.With addition of0-1% Ni,the volume fraction of B2-CuZr increases gradually,When the 1% Ni are added,the volume fraction of the B2-CuZr crystalline phases is 33%.However,this scenario is contrary with further Ni additions.(2)Combined experimental results with FES,deformation mechanisms contributing to the improved mechanical properties for the present MGMCs,especially in compression,related to the stress-induced martensitic transformation of the crystalline phase and the strong interaction between the shear bands,cracks and the ductile B2 crystalline phase is stated.while upon tension,the intrinsic reason for the lack of plasticity is that the interparticle spacing and the plastic zone size of the glassy matrix do not satisfy the matchingrelationship,leading to a rapid propagation of shear bands around the B2 crystalline particles.Consequently,the good tensile plasticity can not be obtained in these composites.(3)The rheological behavior of the CuZr-based BMG composite in the supercooled liquid region is sensitive to the temperature and the strain rate.The flow stress and the peak of the “stress-overshoot” increased with the decreasing strain rate and the increasing temperature.(4)The flow stress of CuZr-based BMG composite is very high,which is due to the stress-induced martensitic transformation of the B2 CuZr phases and the crystallization of the amorphous phases.Because of the effect of heat and stress,the B2 Cu Zr phases can be transformed into B19'martensite phases,which makes the hardness of the composites increase.So the comparison of the rheological behavior of the CuZr-based BMG composite between the dendrite reinforced composites in supercooled liquid region is equivalent to the comparison of the rheological behavior of the composite including the “soft”amorphous matrix,B2 CuZr phases and the “hard” B19'martensite phase between the composite including the “soft” amorphous matrix and the “hard”dendrites at room temperature.Even though the volume fractions of dendrites is very high,the flow stress of the two composites is similar.(5)Upon dynamic loading,because B2 CuZr phases can not prevent the rapid propagation of shear bands in a short time,the fracture strain of CuZr-based BMG composite decreases.In addition,the composite exhibitsnegative strain rate sensitivity,mainly due to the thermal softening within shear bands in the present composite.