The Research On Casting Properties Of Zr-based Amorphous Alloy

Bulk amorphous alloy is characterized by high strength and high hardness. It is very difficult to shape at room temperature either by machining or plastic processing and this limits the bulk amorphous alloy applied as the next-generation structural materials. At present, the molding method of bulk amorphous alloy is restricted to the super-plastic forming, which requires high quality molding equipments and processes, and the type of the forming components are also limited.Series of Zr-based alloys were prepared with copper mold casting method. The influences of the chemical compositions, casting temperature and cooling rate of the cooper mold on the glass-forming ability (GFA) and the mechanical properties of the above alloys were studied by the X-ray diffraction (XRD), differential scanning calorimetry (DSC), the compression test and scanning electron microscope (SEM).The GFA and the mechanical properties of (Zr0.55Al0.10Ni0.05Cu0.30)100-xFex (x= 0,1,5,10) have been analyzed. The result shows that when x= 1%, the linear elastic strain will take place firstly and the plastic deformation of the alloy will happen after reaching the critical value. The plastic Strain is 5.9% and the fracture strength is 1.89GPa. When x= 0,5%, and 10%, the linear elastic strain will take place; and the alloys will break when the fracture strength reaches the critical values of 1.75 GPa, 1.38GPa, and 1.57GPa, respectively. on the other hand,the addition of Fe has affected on glass-forming ability.When the Fe-added is 1%, the glass transition point Tg turns from 673K to 684K, the crystallization temperature Tx increases from 757K to 761K, and the super-cooled temperature rangeΔTX decreases from 84K to 77K; when the Fe-added reaches 5%, the Tg turns from 684K to 704K, the Tx increases from 761K to 767K, and theΔTx decreases from 77K to 63K.this shows that the glass-forming ability and stability decrease due to the addition of Fe to Zr55Al10oNi5Cu30.The casting temperature has an important impact on the mechanical properties of amorphous alloys. The step cut samples of Zr55Al10Ni5Cu30 with diameters ofΦ3mm,4mm,and 6mm are prepared at different input voltages (7kv,8kv,9kv,10kv) by the copper mold casting method and the room temperature compression test on these samples are carried out. We get the result that for theΦ3mm amorphous alloy sample, the fracture strength of compression 1.65GPa,1.74GPa,1.75GPa,and 1.91GPa respectively, rises along with the increase of the temperature; when the input voltage is 10kv, the plastic strain is 2%. For the samples ofΦ4mm andΦ6mm, the fracture strength rises with increasing the casting voltage first and then decreases; it reaches the maximum by the input voltage of 9kv.The mechanical properties of the step cut sample with diameters ofΦ3mm,4mm, and 6mm and wedge-shaped samples are studied with room temperature compression and microhardness methods. The fracture strength of these 3 amorphous alloys with different diameters are 1.91GPa,1.84 GPa,and 1.69 GPa,respectively;and the plastic strain are 2%,0.15%,0, respectively. The microhardness analysis of the wedge-shaped samples shows that along the longitudinal centerline of the sample,the Vickers hardness first increases from 642 to the largest 710,and then reduced to about 570. The study reflects that the section size will affect the cooling rate of the melt, and thus influences the micro-structure and the mechanic properties of the amorphous alloy.