Al-based Amorphous / Nano-composite Material Of Amorphous Forming Ability And Thermal Stability

According to the primary experiential principle of designing amorphous alloy systems, the Al-Ni-Zr-Cu-Y alloy system was planned in this work. The alloy ribbons had been prepared by single roller melt-spinning process under vacuum and atmosphere conditions. The three kinds of alloy systems are Al80Ni10Zr8-xCuxY2(x=1,2,3,5), Al80Ni15-xZr3CuxY2(x=0,1,3,4,6,7,9) and Al80Ni10ZrxCu5Y5-x (x=0,1,2,4). The ribbons were investigated by X-ray difftaction(XRD),differential scanning calorimetry (DSC) and scanning electron microscope(SEM).The effect of Ni, Zr, Cu and Y elements on the glass forming ability and the thermal stability of the alloy system has been investigated.It would be found that the existence of broad diffraction peak can be found in the curves of Al80Ni10Zr3Cu5Y2 amorphous alloys that were fabricated under vacuum and atmosphere conditions, indicating the existence of a single amorphous phase. So it indicates that the fabricating conditions are not very stringent for Al-Ni-Zr-Cu-Y alloy system and the glass forming ability is strong.Among amorphous alloys mostly, the prepeaks exist in the small-angle portion of the XRD curves and the curves show the very small prepeak of the former at 21?approximately and the later at 202. The existence and stability of prepeak corresponding to the stability of chemical short - range structure is in relation to the stability of amorphous alloys. The components and atomic radius of elements including Ni, Zr, Cu and Y have effect on the glass forming ability and the thermal stability of alloys, which is same to the negative mixed heat between these elements and Al, but the synthetical affection of these factors is the most important. Among the three kinds of alloy systems, the glass forming ability of Al80Ni15-xZr3CuxY2(x=0,1,3,4,6,7,9)and Al80Ni10ZrxCu5Y5-x (x=0,1,2,4) alloy systems is strong, the small atomic radius of Ni and Cu of the former and the high negative mixed heat of Al-Ni induce the strong glass forming ability in this alloy system, the big atomic radius of Zr and Y of the later and the high negative mixed heat of Al-Zr and Al-Y induce the strong glass forming ability in this alloy system.Among the three kinds of alloy systems, the intermetallic compounds including Al2Zr,Zr2Al3 and Ni42Zr58 disperse on the amorphous matrix. Among the amorphous and the crystalline phase in amorphous mostly, Al2Cu phase disperse on the matrix. In the DSC curves of Al-based amorphous alloys, no incubation stage is seen for the first exothermic peak. The reason is the existence of the multi- short - range order structure in the liquid state alloy of high temperature that the formation of quenching state pre-existing nuclei. As a result of the existence of quenching state pre-existing nuclei, there is only a growth reaction and not the nucleation reaction in the annealing process. The onset temperature of Al80Ni10Zr7Cu1Y2and Al80Ni14Zr3Cu1Y2 amorphous alloys are 371.9C and 313.9C and the thermal stability of the two amorphous alloys are high. The high negative mixed heat of Al-Zr and Al-Ni and the big atomic radius of Zr of the former and the small atomic radius of Ni of the later and the little component of Cu induce the high thermal stability of the two kinds of alloys.In Al80Ni15-xZr3CuxY2 (x=0,1,3,4,6,7,9) amorphous alloy system, the primary crystallization temperature decrease with the increase of content of Cu. The melting point of Al-Cu intermetallic compound is lower than that of Al-Ni intermetallic compound, So the addition of Cu in Al-Ni-Zr-Y alloy system induce that the decrease of the crystallization temperature of amorphous. The XRD curves and microstructure of Al80Ni10Zr3Cu5Y2 and Al80Ni10Zr7Cu1Y2 amorphous alloys after annealing have been observed, the fine average crystals size have been observed in the two kinds of amorphous alloys after annealing under 598K and 673K. The distribution of crystal is even. The fine crystals can be obtained in Al80Ni10Zr3Cu5Y2 amorphous alloy after annealing under 658K. The result indicates that the addition of Cu and Zr induce f...