Bulk Amorphous Alloy Forming Ability Of Cuzral Department, The Rare Earth Elements And Mechanical Performance Study

A series of CuZrAl-based bulk metallic glassy(BMG) alloys were prepared by means of copper-mold vacuum suction casting. The glassy structure, thermal stability, glass-forming ability(GFA) and mechanical properties of these alloys with nominal composition of Cu₄₆Zr_47-xAl₇M_x(M=Ce,Pr,Tb,Gd;x=2,4,5) were investigated by differential scanning calorimeter(DSC), X-ray diffraction(XRD), scanning electron microscope(SEM), Vicker's hardness, compression tests. The results are summarized as follows.(1) A series of Cu₄₆Zr_47-xAl₇M_x(M=Ce, Pr, Tb, Gd;x=2,4,5) amorphous alloy were prepared by using rare-earth elements Ce, Pr, Tb, Gd to substitute the same quantity of Zr in the Cu₄₆Zr₄₇Al₇ system. The maximal BMG dimension(t_max) of the series of alloy added with Ce, Pr, Tb, Gd are 5mm, 5mm, 5mm, 8mm, respectively.The glass-forming ability(GFA) of CuZrAl-based amorphous increase first and then decrease with increasing elements content of Ce and Pr, and the optimal content is 4at.%. The increasing content of Tb affect the GFA of the alloy littlely. When added 5at.% Gd to the alloy, the GFA increases greatly, an amorphous alloy of Cu₄₆Zr₄₂Al₇Gd₅ with a diameter of 8mm is prepared.As to the amorphous alloy Cu₅₀Zr₅₀, when 6at.% Ce or Pr is added to substitute the same quantity of (CuZr), it can't improve the GFA of the alloy. When added 6at.% Ti to the alloy, it presents amorphous mainly while v/ith some crystal in the sample of 3mm. When added 4at.% Al, it is difficult to prepare amorphous alloy with 3mm diameter, however, when the content of Al increase to 6at.% and 8at.%, it can be prepared.(2) Thermal stability was examined by DSC at heating rate of 20℃/min. With the addition of Ce, Pr, Tb, Gd to the alloy, the onset crystallization temperature(T_x) and the crystallization peak temperature(T_p) all move to the low temperature, and T_x is about 480 ℃, T_p is about 490 ℃. While the change of T_g is more complex than the above, it changes with the difference of the element and its content. Most of the the supercooled liquid region(△T_x) decrease to less than Cu₄₆Zr₄₇Al₇ except Cu₄₆Zr₄₂Al₇Gd₅.Cu₄₆Zr₄₃Al₇M₄(M=Ce, Pr) and Cu₄₆Zr_47-xAl₇M_x(M=Tb, Gd;x=2,4,5) amorphous alloy allexhibitc large GFA and good thermal stability. The Tg is above 410"C, and the ATX is between 47-77K, all the BMG alloys exhibite only one main exothermic peak. The ATX of Cu46Zr42Al7Gd5 amorphous alloy is 76.8°C, about the same as that of Cu46Zr47Al7 amorphous alloy.(3) The values of activation energy AEg, AEX and AEP for Cu46Zr42Al7Gd5 BMG alloy have been obtained at the heating rate of 12°C/min, 20°C/min and 28°C/min with Kissinger and Ozawa equations as follows: 340.7 kJ/mol, 211.3kJ/mol, 211.3kJ/mol and 334.8kJ/mol, 210.3 kJ/mol, 210.3kJ/mol, respectively.The values obtained with Kissinger equation are just a little higher than those with Ozawa equation, but the vaviation trend of these parameter is consistent greatly.(4) The Vicker's hardness of the series BMG were investigated. The Vicker's hardness changes with the difference of rare-earth elements and its content. When added 4at.% Ce, Pr, Tb, Gd, the Vicker's hardness of Tb alloy exhibites the largest, Hv568, while that of Pr alloy the least, Hv479. The Vicker's hardness of the alloy added Tb and Gd decrease with the increase of rare-earth content.(5) The compression properties of the series BMG rods were investigated. The fracture strength( o cf) for Cu46Zr43Al7M4(M=Ce,Gd,Tb) BMG alloy are 407MPa, 712MPa, lOHMPa respectively and their elongation( e f) are 1.56%, 2.8%, 3.3% respectively. Compressive samples are always fracture or crack nearly parallel to the compressive axis, and the compressive fracture angles are about 0° and all exhibite brittle fracture.