| In the cryogenic temperature environment,the movable parts of traditional crystalline components or equipment will be stuck,cracked,characteristic change and even brittle fracture.Due to special properties of higher strength and better plasticity at cryogenic temperature,bulk metallic glass has great application advantages in extreme conditions such as polar scientific research and aerospace.In order to seek bulk amorphous alloy materials with excellent comprehensive properties at cryogenic temperature extreme conditions,the(Zr0.6336Cu0.1452Ni0.1012Al0.12)100-xTmx(x=0?5at.%)bulk amorphous alloys were fabricated by copper mold suction casting method.Firstly,the effects of Tm content on mechanical properties and corrosion resistance of bulk amorphous alloy were characterized by XRD,TEM,universal mechanical testing machine and electrochemical workstation,so as to optimize the alloy composition with excellent comprehensive properties at room temperature.Furthermore,the quasi-static and dynamic compressive mechanical properties of bulk amorphous alloy were studied by mechanical testing machine and Hopkinson pressure bar at cryogenic temperature.The change mechanism of mechanical properties at cryogenic temperature was analyzed by the fracture morphology and the serrated rheology of bulk amorphous alloys.Finally,the effects of temperature mutation on mechanical properties and corrosion resistance of bulk amo rphous alloys were investigated by cold-heat treatment from the perspective of practical application.This study provides a theoretical basis for the application of bulk amorphous alloy at cryogenic temperature extreme conditions,and has important theoret ical and practical significance for promoting the engineering application of amorphous alloy.The main conclusions are as follows:(1)With the increase of Tm content,the plastic strain and compressive strength of bulk amorphous alloy with diameter of 2 mm increase gradually.Compared with the original alloy with x=0,the alloy with x=3 has good thermal stability and glass forming ability.The compressive strength of the alloy increases from 1493 MPa to1669 MPa,and the plastic strain increases from 5.90%to 21.01%.In addition,the electrochemical corrosion test results show that the alloy with x=1.5 has strong corrosion resistance,indicating that the appropriate amount of rare-earth element Tm can improve the mechanical properties and corrosion resistance of the bulk amorphous alloy.(2)The experimental results of quasi-static and dynamic compression for specimens with diameter of 3 mm at cryogenic temperature show that the compressive strength of the alloy increases with the decrease of temperature due to the higher atomic bonding strength at cryogenic temperature.Under quasi-static compressive experiment,when strain rate of 1×10-4s-1,the plasticity of the alloy increases with the decrease of temperature,especially the plastic strain reach 13.7%at 77 K,the alloy is brittle fracture at strain rate of 1×10-3 s-1.Meanwhile,under dynamic compressive experiment with high strain rate,the alloy does not show obvious plastic deformation,and the compressive strength shows negative strain rate sensitivity.Th e reason is that the strain energy is released instantly and accompanied by local heating during dynamic loading.When the local temperature is close to2),the viscosity in the shear band decreases rapidly,resulting in show negative strain rate sensitivity.(3)The bulk amorphous alloy specimens with diameter of 3 mm were cold-heat treated for 30 min,60 min and 90 min.It is found that the compressive strength of the bulk amorphous alloy increases from 1703 MPa to 1805 MPa when the cold-heat treatment time is extended from 30 min to 90 min.Electrochemical corrosion experiments show that the alloy in 3.5 wt.%Na Cl solution has a small self-corroding current density and a large impedance,which indicates that the longer time treatment can improve the corrosion resistance of bulk amorphous alloy. |
PDF Full Text Request