Synthesis And Mechanical Properties Of Zr-Cu-Al Bulk Metallic Glasses Composites

This paper was focused on the relationship and internal mechanism amongprocesses-structures-performance about rich Zr matrix Zr60+xAl10Cu30-x（x=0,4,8,12,16at.%） alloy system. Bulk metal glass （BMG） and its composite of Zr60+xAl10Cu30-x（x=0,4,8,12,16at.%） are prepared by maglev smelting and copper mould suctionmethod under controlling the conditions of alloy melt heating and solidification.Several factors including melt-overheating temperature and the change of coolingrate etc. influencing on the microstructures, thermal stability,glass-formingability（GFA）and the mechanical properties were studied.Zr₆₀Al₁₀Cu₃₀and Zr₆₄Al₁₀Cu₂₆BMG exhibits higher thermal stability andstronger glass-forming ability in the ternary alloy system. Its overcooling liquid areawidthΔTxare54K and65K respectively, simplifing glass transition temperatureTrgare0.588and0.567respectively, γparameters are respectively0.400and0.397.The critical thickness of Zr₆₀Al₁₀Cu₃₀bulk glassy alloy is about up to6mm,and thecritical size of Zr₆₄Al₁₀Cu₂₆BMG is only3mm. It shows that glass formation abilityof the latter is much weak than the former. This conclusion and thermalcrystallization of Zr₆₄Al₁₀Cu₂₆BMG are consistent. The characteristic temperatureapparent activation energy were calculated by the Kissinger. The results show thatthe activation energies of glass transition （Eg）, crystallization （Ex） and peakcrystallization （Ep） are487kJ/mol,200kJ/mol and244kJ/mol,respectively.The mechanical behavior changes distinctly due to the presence of differentmicrostructure. The Ф4mm Zr₆₀Al₁₀Cu₃₀BMG exhibits compressive strength of1595MPa,compressive fracture strength of1280MPa with plastic strain of1.95%.The fracture surface appearance presents typical amorphous nervation andbrittleness smooth area. The Ф6mm BMG composites containing the brittlecrystallizing phase—AlCu₂Zr with DO3structure and Cu10Zr7with orthorhombicstructure, exhibits compressive strength of1345MPa with plastic strain of0.5%.The final fracture behavior is controlled by competition of plastic phase andcrystallizing phases,which cause the Ф6mm samples destructive fault by brittlefracture.The Ф3mm Zr₆₄Al₁₀Cu₂₆BMG exhibits compressive strength of1610MPa,compressive fracture strength of1580MPa with plastic strain of6.34%. Compressive stress-strain curves appears the typical “work-hardening” after theelastic deformation. It is the best of comprehensive mechanical properties at roomtemperature. At the same time, internal mechanism was analyzed to improve themechanical properties.The fracture behavior of of the as-cast Zr₆₀Al₁₀Cu₃₀and Zr₆₄Al₁₀Cu₂₆BMG andcomposites rods at different diameter are to shear fracture way. The angle betweensample fracture surface and stress axis is about to less than45. Fracture surfaceshows flattening. The secondary shear bands can be observed at the side of sample,especially Zr64Al10Cu26alloy rods still can observe tertiary shear bands. Theinteraction amongst shear bands obviously presents mesh structure in sample side.The intersecting, branching and sliding of multiple shear bands and the largercritical shear offset are the major reason for the higher compressive plasticity in theZr64Al10Cu26bulk metallic glass. However, compressive fractures surfaceappearance of Zr68Al10Cu22, Zr72Al10Cu18and Zr76Al10Cu14alloy rods exist greatdifferences along with the reduction of Cu.The proper overheating level of alloy melt not only affects alloy glassformation ability, also influence alloy microstructures and mechanical properties. InZr60+xAl10Cu30-x（x=8,12,16at.%） alloy system, how many ZrCu martensitic phasetransform into Zr₂Cu and Cu₁₀Zr₇brittle crystal phase during solidification process,which decided the mechanical properties and final fracture behavior of the alloy.Therefore, reasonable composition matching and crystal phase type and sizecontrolling is the key for improving mechanical behavior of the alloy in a sense.