Synthesis,Thermal Stability And Mechanical Properties Of Zr-based Glassy Alloys And Their Composites

Zr-based glassy alloys have high glass-forming ability,high strength,high elastic strain limit and large width of the supercooled liquid region that is easy to process and mold,which have attracted great attention from fundamental science and practical applications.However,lack of plasticity makes the glassy alloys to catastrophic failure in load-bearing conditions at room temperature and the poor thermal stability makes it easy to crystallize during use,which limits their application prospect.Thus,it is of great significance to develop Zr-based glassy alloys and their composites with good plasticity and high thermal stability.In this paper,ternary and multi-element Zr-based alloy systems were designed by alloying,substitution with similar elements and increasing the number of components.Glassy alloy ribbons and bulk metallic glassy composites were prepared by melt-spinning technique and copper injection casting,respectively,and their microstructure and properties were studied.Ternary(Zr_0.58Cu_0.42)_100-xAl_x（x=3,5,7,10）bulk metallic glassy composites with good plasticity were prepared.The effects of alloying of Al on microstructure,thermal stability and mechanical properties for Zr-rich Zr-Cu alloys were investigated.The results show that proper alloying of Al（3～10 at.%）can improve the glass-forming ability of Zr₅₈Cu₄₂ alloy.With the increase of Al content,phase evolution in the composite is[glass+Cu₁₀Zr₇+Cu Zr₂+B2]→[glass+B2+Cu₁₀Zr₇]→[glass+Cu₁₀Zr₇].The Zr-Cu-Al bulk metallic glassy composites exhibit high strength and good plasticity under compression at room temperature.When Al content is 5 at.%,the composite exhibits the best mechanical properties:the yield strength is～1444 MPa,the fracture strength is～1900 MPa,and the plastic strain is～6%.The enhanced plasticity is due to martensite transformation of B2 phase in the composite and the seeding,branching and multiplication of shear bands in the glassy matrix.Glassy ribbons and as-cast rods of Zr₅₀M₅₀,Zr₅₀（M,Ag）₅₀ and Zr₅₀（M,Pd）₅₀（M=Fe,Co,Ni,Cu）multicomponent alloys were prepared.The effects of different components on their microstructure,thermal stability,crystallization behavior and mechanical properties were investigated.It was found that the thermally induced crystallization phases of the three glassy alloys were mainly B2 phase.The Zr₅₀M₅₀glassy alloy exhibits a certain degree of tensile plasticity,which is due to deformation-induced crystallization of glassy phase.The effect of“transformation induced plasticity”makes Zr₅₀M₅₀as-cast rod show good plastic deformation ability,with the plastic strain over 20%and compressive strength over 1700 MPa under compression at room temperature.Glassy ribbons and as-cast rods of Zr₆₅（Al,Fe,Co,Ni,TM）₃₅（TM=Cu,Pd or Ag）multicomponent alloys were prepared.The effects of TM element on their microstructure,thermal stability,crystallization behavior and mechanical properties were investigated.The developed Zr₆₅（Al,Fe,Co,Ni,TM）₃₅（TM=Pd or Ag）multicomponent glassy alloys exhibit high thermal stability and can remain a glassy phase when annealed above the crystallization temperature for 14.4 ks.This strong resistance to crystallization results from the large atomic radii differences between solute elements.