Study On The Strenghthening And Toughening Of Cu-Zr-Al-Y Glassy Alloy And Its Horizontal Continuous Casting

Bulk metallic glasses?BMGs?possess unique physicochemical properties owing to the absences of grain boundaries and dislocation slip deformation,which make them promising engineering structural materials.However,on the one hand,the preparation cost,efficiency and complexity of preparation process make it difficult to prepare large-size glassy alloys.On the other hand,the plastic deformation mechanism of glassy alloys depending on highly localized shear bands leads to a minor macroscopic plastic strain,these factors have greatly limited the commercialization and industrialization of glassy alloys.In view of the above problems,the preparation of bulk metallic glass composites?BMGCs?by isothermal annealing was carried out to enhance the hardness,compressive strength,plasticity and toughness via in-situ nanophase strengthening effect.The strengthening and toughening methods suitable for Cu-Zr-Al-Y amorphous alloys were investigated.Moreover,this paper introduces the self-designed double-chamber electromagnetic horizontal continuous casting?HCC?for continuous fabrication of large-size glassy alloy plates.The preparation efficiency of amorphous alloys can be greatly improved by this near-net forming technology,which is of great significance to the industrialized production of BMGCs.?1?(Cu₄₇Zr₄₅Al₈)_98.5Y_1.5 glassy alloys with wide super-cooled liquid zone??T_x>80 K?and compressive fractural strength near 2 GPa were prepared via cooper-mold injection-casting.Cu-Zr-Al-Y BMGCs with different crystallinities were fabricated via isothermal annealing at680⁷60 K for 20 min,the relationship between microstructures and mechanical properties were investigated.The results indicate the increase of crystalline volume of(Cu₄₇Zr₄₅Al₈)_98.5Y_1.5 BMGCs with the rising annealing temperatures,while their phase transition with rising temperature follows Am?amorphous state??Am+Cu₁₀Zr₇?Am+Cu₁₀Zr₇+AlCu₂Zr+Al₂Zr.Precipitation strengthening and structural relaxation during annealing enhance the alloy microhardness remarkably.The TEM results show that Cu₁₀Zr₇with a size of 6¹2 nm develop the?_f to 1950 MPa?After annealing at 700 K,the?_f decreases slightly and plasticity increases at the same time.the?_f decreases greatly after annealing at720⁷60 K,the fractural surfaces reveal obvious ductile and brittle fracture zone,and the proportion of brittle fracture area increases with the annealing temperature.?2?The addition of 1 at.%Nb enhances the GFA and?_f of(Cu₄₇Zr₄₅Al₈)_98.5Y_1.5.5 BMGs owing to the Cu₁₀Zr₇ with the size of 12²6 nm during the onset of crystallization.The?_f of Nb1 BMGCs increases to 2080 MPa after annealing at 700 K for 30 min while the microhardness of the samples annealed at 800 K for 60 min increases to 712 HV.?3?(Cu₄₇Zr₄₅Al₈)_98.5Y_1.5.5 alloys were selected to carry out the HCC experiments.The influences of the superheats to the quality and microstructure of the plates were investigated,the results show that the central parts of the plates were almost fully-amorphous under the superheat of 120 K,while the microhardness reached 492 HV and the compressive fractural strength reached 1525 MPa.The addition of electromagnetic field enhances the mold-filling and improve the microstructure of plates.The amorphous content increases to 89.4%with a 18KHz electromagnetic field.The optimum continuous casting process with 3 mm/s continuous casting rate,4 s pull-out and 4 s stop,a superheat of 120 K and 18 KHz electromagnetic field has been developed.