On The Mechanical And Crystallization Behaviors Of Zr(Co,Ni)Al Bulk Metallic Glasses

The specific strength refers to the ratio of the strength and the density of materials.In the aviation,aerospace,automotive,racing and other applications,it is required both light weight and high strength.The internal atoms of bulk metallic glass?abbreviated as BMG?are "frozen" in the liquid,whose atomic structure is short-/medium-range order,long-range disorder,without structural defects,like grain boundry and dislocation,making BMGs being used as structural and functional materials.How to improve its glass forming ability,mechanical properties?such as specific strength,plasticity,toughness,etc.?and anti-crystallization ability have become the main bottleneck for the large-scale application of BMGs.In this paper,the influence of chemical elements on the mechanical properties and crystallization behaviors of BMG were investigated.The glass forming ability,mechanical properties and thermodynamic behavior of Zr₅₆Co₂₄Al₂₀ BMG were studied.The influence of Ni partial substitution Co on the thermal stability in supercooled liquid region,glass forming ability and crystallization behaviors of Zr₅₆Co_18-xNi_xAl₁₆?x = 0,2,4 and 8?BMGs was also studied.The following important conclusions can be drawn:Firstly,the completely amorphous Zr₅₆Co₂₄Al₂₀ alloy is obtained by water-cooled copper mold.The yield strength of the Zr₅₆Co₂₄Al₂₀ alloy is more than 2GPa and the ultimate fracture strain is more than 10%.With the increasing Al/Co ratio in the Zr₅₆Co_18-xNi_xAl₁₆?x = 12,16 and 20?BMGs,the compressive plasticity and specific strength are improved obviously.The specific strength of Zr₅₆Co₂₄Al₂₀ metallic glass is obviously higher than that of 316L stainless steel,typical light alloy materials and Pd-based,Cu-based,Zr-based bulk metallic glasses.The thermal stability in the supercooled liquid region is better.With the increasing Al element,however,it is easier to redistribute the atoms in the crystallization process,therefore,the crystallization activation can be reduced.The large amount of multiple shear bands formed on the outer surface of the compressed sample effectively reduces the local energy concentration and leads to a large compressive plasticity.The existence of the veins on the fracture surface proves the pure shear process in the fracture plane of the amorphous alloy.Secondly,the glass transition temperature of Zr₅₆Co_18-xNi_xAl₁₆?x= 0,2,4 and 8?BMG increases and then decreases with the increasing Ni content.The width of the supercooled liquid region also appears the same trend.The y parameter is also decreased first and then increased,indicating that the change in Ni content can affect the glass forming ability of the alloys;the change of Ni content can improve the anti-crystallization ability of the BMGs.