Microstructure Evolution And Plastic Deformation Behabior In A Zr-based Bulk Amorphous Alloy After Cyclic Loading-unloading Compression Test

The macroscopically plastic deformation of bulk amorphous alloys at room temperature was known to be highly-localized to narrow shear bands,and the room temperature brittleness was strongly correlated with their highly-localized deformation behavior even at a quasi-static strain rate. Thus, the spatial multiplication of shear bands was an effective manner to improve the plasticity of bulk amorphous alloys.In the paper, the typical Zr-based bulk amorphous alloys, r52.5Cu17.9Ni14.6Al10Ti5 (Vit. 105) were chosen and prepared by arc melting.The pretreatment test on amorphous alloy samples with normal aspect ratio(2:1) were used cyclic loading-unloading mold under the conditions of geometrically constrained with different load or frequency, in order to investigate the plastic deformaton behavior of bulk amorphous alloys at RT.The microstructure and mechanical properties of pretreatment bulk amorphous alloys were studied.lt was also studied that the effect of different load or frequency on the mechanical properties of alloy samples. The serrated flow were found and it's correlation with the plastic deformaton behavior of Zr-based bulk amorphous alloys was studied.The pretreatment test result showed that the crystallization of amorphous alloys was not found.But the internal atomic structure was changed and there was residual stress.The structural relaxation temperature of alloys was lower than that of as-cast alloys and it was showed a downward trend with the increase of the load and frequency.The pretreatment test increased the value of free volume among bulk amorphous alloys and the loading frequency has a great influence on the value of free volume and ?Hr.When the frequency increase to 30Hz, the value of ?Hr increased to -11.3 J/g.The value of micro-vickers hardness decreased with the value of load.It meant the softening phenomenon of the alloys after high load treatment was obviously.The result showed that hardness value of the alloys with 7KN and 8KN pretreatment was lower than that of the as-cast alloy. The plastic strain value of the pretreatment alloys were higher than that of as-cast alloy, which indicated that the cyclic loading process improved the plasticity of the alloy samples.It could be say that the pretreatment alloy with 6KN, 20Hz has a best plastic deformaton behavior.The SEM images of fracture surfaces and profile of the pretreatment Vit.105 amorphous alloys showed the increase of load and frequency caused a significant temperature rising among alloy samples. At the same time, the number of the shear bands on profile were increased, and the staggered bands had hindered the expansion of the shear zone.The serrated flow were found from the compression stress-strain curves.Analysis of serrated flow showed that the plasticity of the alloys was improved due to not only the increasing of the free volume among alloys after pretreatment test, but also the increased number of the shear bands.Beside, the value of viscosity among pretreatment alloy samples was small and the temperature replied fast.Therefor, the synergistic effect had improved the plasticity of the Zr-based bulk amorphous alloys.