The Fabrication Of Zrcu-based Bulk Metallic Glasses Reinforced By Ductile Crystallines And The Study Of Compressive Properties In Room Temperature

ZrCu-based bulk metallic glasses(BMGs) have become one of most active fields in the research of advanced materials due to their unique mechanical,chemical and physical properties.In this dissertation,the ZrCu-based bulk metallic glasses(BMGs) plates and ZrCu-based BMG-based composites plates with 14 compositions of (Zr50Cu50)_100-xAl_x(x=0,2,4,6,8,10),Zr_55-xCu_45-xAl_2x(x=0,1,2,3,4,5), (Zr48.5Cu46.5)_100-xAl_x(x=5,10)(nominal composition,at.%),respectively,which were chosen by Zr-Cu-Al alloy systems,are fabricated by arc melting copper molding method.By using X-ray diffractometry(XRD),metallographic microscope(OM), differential scanning calorimetry(DSC),transmission electron microscopy(TEM), mechanical loader tester(MLT) and scanning electron microscopy(SEM),the microstructure,thermodynamics,glass forming ability(GFA) and room temperature properties under uniaxial compression are systematically investigated.The present work reveals that the characteristics of the variation in the microstructure of the alloy plates,glass forming abilities and the room temperature mechanical properties under compression with corresponding variations of the Al addition into ZrCu-based BMG and the composites.Thereby,ZrCu-based BMG composite with ZrCu martensitic phase in the amorphous matrix,whose composition is Zr_48.5Cu_46.5Al₅,is successfully fabricated.Zr-Cu-Al BMG plates have an excellent GFA.When the addition of Al component≥6 at.%,the microstructure of the(Zr50Cu50)_100-xAl_x(x=6,8,10) and Zr_55-xCu_45-xAl_2x(x=3,4,5) alloy plates are unique amorphous.The microstructure of the Zr₄₆Cu₄₄Al₁₀ alloy plate is homogenous amorphous phase except some CuZr nanocrystals with B2 b.c.c,structure sparsely distribute in the amorphous matrix. When the addition of A1 component＜6 at.%,various crystalline phases with different microstructure exist in the center area of the amorphous alloy plates.Besides, the precipitate in Zra9Cua9Ale,Zr₅₀Cu₅₀ and Zr_48.5Cu_46.5Al₅ alloy plates is coarse spherical ZrCu martensitic phase.The precipitate in other 5 alloy plates with the compositions Zr₄₈Cu₄₈Al₄,Zr₅₃Cu₄₃Al₄,Zr₅₄Cu₄₄Al₂ and Zr₅₅Cu₄₅,respectively,is the spherical dendrites composed of CuZr intermetallic compound.The spherical dendrites are distributed in the center area of the alloy plates except the Zr₅₃Cu₄₃Al₄ alloy with the microstructure that partial diffused spherical dendrites distributed in the homogenous amorphous matrix.The results of the room temperature quasi-static uniaxial compression tests demonstrate that 6 BMG alloy plates have significantly high yield strengths.After yielding,these materials experienced a short work-softening behavior which increases the plastic strain before failure.The mechanical properties under compressive loading of the 3 BMG composites alloy plates enforced by ZrCu martensitic phases are remarkably improved.Moreover,the Zr_48.5Cu_46.5Al₅ alloy plate have the highest fracture strength(σ_f^c=～2081 MPa) together with large plastic strain(ε_p=～5.5%) compared to other alloy compositions,which has been found to be one of best compositions with corresponding compressive properties improved excellently, comparing to other ZrCu-based BMG developed last few years.Thereby,the machnism of the plasitic improvement are mainly concentrated in micrometer-scale martensitic crystallines distributed at the amorphous matrix effiently hindering the propagation of the shear bands and inducing the formation of multiple shear bands. However,the corresponding mechanical properties of the other 5 BMG composites alloy plates with the precipitate of CuZr spherical dendrites are not significantly improved,except that of Zr₅₃Cu₄₃Al₄ alloy plate with some partial diffused spherical dendrites distributed in the homogenous amorphous matrix,leading to the "work-harding" behavior.The fracture of the Zr₄₆Cu₄₄Al₁₀ alloy plate exhibits classically brittle features because of the low content of nanocrystals particles sparsely distributing in the amorphous matrix,which can not hinder the primary shear bands propagating through the whole sample.It indicates that the reinforcements to improve the plasticity of BMG must hinder the the formation and propagation of the highly localized single shear band.