Preparation And Performance Study Of The Y-based Amorphous Alloy

Since the first report of successful preparation of amorphous alloysby P.Duwez et al. the materials have attracted increasing interests due totheir unique mechanical, magnetic, electrical and chemical properties.Searching alloys which have more powerful glass forming ability(GFA)is our object. The rare-earth-based amorphous alloys, which havepotentials for application as functional materials, have been found inmany alloy systems.This work focuses on analysis and studying of the new Y-(Ce, Pr,Nd, Sc, Zr)-Al-Co amorphous alloys, including the glass-formingability(GFA), thermal stability and mechanical properties. Amorphousribbon specimens were prepared by a single roller melt-spinningtechnique in argon atmosphere. We choose the model systemY₄₆Zr₁₀Al₂₄Co₂₀ and Y₄₁Sc₁₅Al₂₄Co₂₀ samples, which have the highestGFA, to study their crystallization kinetics and mechanical propertiesusing differential scanning calorimeter and Microhardness Tester. Theresults are as follows:(1) The results show that the addition of Ce, Pr and Nd element(5～20at.%) improves GFA of Y₅₆Al₂₄Co₂₀ amorphous alloy, GFA ofY_56-xM_xAl₂₄Co₂₀(M=Ce, Pr, Nd, x=5, 10, 15, 20) alloys increase with theincreasing of M content. The maximal reduced glass transitiontemperature(T_rg), the supercooled liquid region (â–³T_x) and parameterγis62K, 0.688 and 0.417, respectively. The addition effects on GFA ofY₅₆Al₂₄Co₂₀ alloys can be explained according to thermodynamics theoryand order-disorder competition of melt microstructure. The resultssuggest that GFA of amorphous alloys can be improved by equiatomicsubstitution, of which electron configurations are different with that ofmain element.(2) The results show that the addition of Zr and Sc element (5～20at.%)improves GFA of Y₅₆Al₂₄Co₂₀ amorphous alloy, GFA ofY_56-xM_xAl₂₄Co₂₀(M=Zr, Sc, x=5, 10, 15, 20) alloys increase with theincreasing of Zr or Sc content. The glass transition (T_g), crystallizationonset (T_x), melting (T_m), T_rg,â–³T_x andγof Y₅₆Zr₁₀Al₂₄Co₂₀ is 660K, 724K, 1026K, 64K, 0.626 and 0.422, respectively. While the values ofY₄₁Sc₁₅Al₂₄Co₂₀ amorphous alloy are 643K, 717K, 967K, 74K, 0.641 and0.436, respectively. We use Zr (10 at.%), which is cheaper, instead ofSc(15 at.%) of Y₄₁Sc₁₅Al₂₄Co₂₀ amorphous alloy to reach similar GFA. Itcan be proved through the elements of alloy system, atomic radius, heatof mixing and electronegativity.(3) Thermal stability of Y-based was examined by DSC at various heatingrates of 10, 20, 30 and 40K/min with Kissinger and Ozawa equations asfollows: The values of activation energyâ–³E_g,â–³E_xå'Œâ–³E_p forY₅₆Al₂₄Co₂₀ amorphous alloy are 390.15kJ/mol, 257.02kJ/mol,267.28kJ/mol and 381.15kJ/mol, 255.54kJ/mol, 265.25kJ/mol,respectively. The values for Y₄₆Zr₁₀Al₂₄Co₂₀ amorphous alloy are415.64kJ/mol, 279.74kJ/mol, 319.15kJ/mol and 405.42kJ/mol,277.44kJ/mol, 315.28kJ/mol, respectively. The values forY₄₁Sc₁₅Al₂₄Co₂₀ amorphous alloy are 474.17kJ/mol, 307.12kJ/mol,291.48kJ/mol and 461.08kJ/mol, 303.56 kJ/mol, 288.72kJ/mol,respectively. The values obtained with Kissinger equation are just a littlehigher than those with Ozawa equation, but the variation trend of theseparameters is consistent greatly. These results show that the glasstransition needs more activation energy than the crystallization process.Calculations of Kissinger equation and Ozawa equation can prove that theexcellent thermal stability is achieved for the V₄₆Zr₁₀Al₂₄Co₂₀ metallicglass.(4) For Y₅₆Al₂₄Co₂₀, Y₄₆Zr₁₀Al₂₄Co₂₀ and Y₄₁Sc₁₅Al₂₄Co₂₀ amorphousalloys, the hardness increases with the reduce of cooling rate. Theinfluence of annealing treatments on the hardness increases withincreasing heat-treatment temperature. It can be explain according to freevolume. We use Zr (10 at.%), which is cheaper, instead of Sc (15 at.%) ofY₄₁Sc₁₅Al₂₄Co₂₀ amorphous alloy to reach equal or better hardness inmelt-spun or annealed states.