The Research On The Behavior Of The Plastic Deformation For Zr₆₅Cu_27.5Al_7.5 Block Amorphous Alloy By Oxygen

Industrial sponge zirconium, lodized zirconium, Cu(99.99% purity), Al(99.99% purity) were used as raw materials. ZrO₂ with high purity was employed to further increase the oxygen content in the alloy made of sponge Zr. The nominal composition Zr₆₅Cu_27.5Al_7.5 ternary bulk amorphous alloy ingots cantaining the oxygen concentrations of 0.06 at % and 0.68 at % were prepared respectively by arc-remelting and then a series of cylindrical rod specimens with different diameter were obtained respectively by Cu-mold casting under different atmosphere pressures. The cylindrical rod specimens with critical diameter of 2mm for the two alloys were validated as monolithic bulk amorphous alloys by X-ray diffraction(XRD) analyses and transmission electron microscopy(TEM) observation. Based on the differential scanning calorimetly(DSC) analyses, the dependence of specific heat and temperature of the two alloys were obtained befor the glass transition region. The study demonsreated that free-volume content of the two alloys decreased dramatically with increasing specimen size. At the same time , for the specimens with the same size , higher oxygen concentration did not decrease the initial free-volume content in the bulk amorphous alloys. For the cylindrical specimens with a normal aspect ratio of 2, room-temperature compression tests were conducted and the compressive engineering strain-stress curves were obtained. It can be seen that for the as- case rods with the same size, the compressive plasticity was dramatically decreased by oxygen.To further understand the change in palstic deformation behavior caused by oxygen, geometrically cantrained compression tests were conducted for the two kinds of alloys with a diameter of 1.5 mm and an aspect ratio of 1. It was revealed that under the compressive deformation, the increase of free-volume content and the shear band' density for the alloy with high oxygen content is lower than that for the alloy with low oxygen content, the precesses of free-volume accumulation and shear band propagation during plastic deformation were pronouncedly retarded by oxygen. It appears that the mechanism for the oxygen-induced embrittlement was closely related with the decreased atomic mobility by oxygen. Based on the DSC analyses for the amorphous ribbons with different oxygen at the different heating rates and the Kissinger plot, the apparent activation energy for previous crystallization peek and main crystallization peek temperatures for the two ribbons were abtained respectively. It can be seen that the oxygen improved the activation energy of alloy, decreased atomic mobility, retared the initiation of shear bands, as a result ,embrittles the alloy. The activation energy may be used as a factor to evaluate the plasticity of monoliyhic Zr-based bulk amorphous alloys with different oxygen concentrations.