| Zr-based bulk amorphous alloys are new metallic materials with a range of excellent properties that have broad application prospects in many fields.However,the inability to process and shape Zr-based bulk amorphous alloys due to their extremely poor room tem-perature plasticity has greatly limited their industrial application in some applications.Bulk amorphous alloys have extremely low viscosity coefficients in the supercooled liquid region（SLR）and exhibit superplastic deformation capabilities,offering the possibility of plastic forming of complex shaped amorphous alloy components.In addition,amorphous alloys processed within the SLR are subject to coupled stress and thermal fields,and their sub-stable structural properties can evolve and affect their service performance.Therefore,studying the deformation behavior and deformation mechanism of Zr-based amorphous al-loys,establishing thermal processing map to obtain the optimal forming conditions,as well as analyzing the effects of high-temperature deformation parameters on the properties and crystallization behavior of the alloy after deformation can help guide the thermoplastic forming of bulk amorphous alloys and advance the process of industrial application of amorphous alloy materials.In this thesis,alloy rods with 3 mm in diameter and 90 mm in length were prepared by copper mold suction casting using the Zr55.7Cu22.4Al14.7Ni7.2 alloy composition with large amorphous formation ability explored by the group.The microstructure,thermodynamic properties,crystallization behavior,deformation behavior and mechanism in the supercooled liquid region were studied by means of X-ray diffractmeter（XRD）,Vickers microhardness tester,differential scanning calorimeter（DSC）and high-temperature uniaxial compression test,etc.The optimum plastic forming conditions were derived,and the effects of high-temperature deformation on the thermodynamic and mechanical performances were investigated.The results show that:（1）The prepared Zr55.7Cu22.4Al14.7Ni7.2 alloy rods have a completely amorphous struc-ture with glass transition temperature,onset of crystallization temperature and peak crystal-lization temperature of 713 K,779 K and 781 K,respectively,and a supercooled liquid re-gion of 66 K,and have strong glass transition kinetics.The crystallization incubation period corresponds to 21.22-3.26 min at 733-758 K,respectively,and shortens significantly with increasing temperature,and the crystallization transition rate accelerates sharply.The crys-tallization behavior is a diffusion-controlled primary or eutectic crystallization with nuclea-tion growth,and the nucleation rate increases with time.（2）The deformation behavior of this alloy in SLR is more influenced by strain rate and test temperature,and less influenced by the degree of deformation.As the degree of defor-mation improves,the plastic deformation behavior of this alloy transforms from inhomoge-neous to homogeneous deformation.As strain rate decreases and the test temperature rises,the steady-state flow stress show a decreasing trend,and the stress overshoot phenomenon gradually disappears,and its viscosity also decreases monotonically,i.e.,there is a critical transformation strain rate for the transformation of Newtonian flow,and its critical transfor-mation strain rate is 1×10-3 s-1,which moves to the high strain rate region with the improve-ment of test temperature.（3）The alloy crystallizes after compressive deformation at high temperature and low strain rate,and the crystallized phase isτ3 phase(Zr51Cu28Al21),which increases the defor-mation resistance,and the degree of crystallization of the alloy increases with decreasing strain rate and increasing test temperature.The alloy remains amorphous after compressive deformation at low and medium temperatures and high strain rates.The optimum thermo-plastic forming conditions for this alloy in SLR range from 740 K to 750 K and 5×10-4 s-1 to5×10-3 s-1.（4）The microhardness of the alloy increased by 4.1%,15.2%,and 13.2%with increas-ing deformation amount and test temperature and decreasing strain rate,respectively,and test temperature and strain rate have a greater effect on the microhardness.The alloy undergoes structural evolution during compression at high temperature possibly producing atomic clus-ters that act as nuclei for crystallization,thus shortening the crystallization incubation period,and strain rate decreases from 7.5×10-3 s-1 to 5×10-4 s-1,the crystallization incubation period decreases from 5.05 min to 3.84 min,the volume fraction of ordered atomic clusters in-creases from 4.5%to 66.7%,but the crystallization transition rate shows a trend of increas-ing and then decreasing.（5）After the alloy is compressively deformed at high temperature,the thermal stability of the structure and the sensitivity of the glass transformation process to the heating rate are improved,and the kinetic effect and the sensitivity of the crystallization process to the heat-ing rate are reduced.As the strain rate decreases,its thermal stability decreases,the sensitiv-ity of the glass transformation and crystal growth processes to the heating rate decreases,and the kinetic effect decreases more significantly,while the sensitivity of the crystallization process to the heating rate remains almost unchanged.This BMG undergoes thermoplastic deformation at 750 K,5×10-3 s-1 to 7.5×10-3 s-1 to obtain products with the best mechanical and thermomechanical properties. |
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