Study On The Effect Of Addition Elements On The Glass Forming Ability And Mechanical Properties Of Cu-Zr Based Alloys

In this paper, the third element M(Y, Gd or Al) will be added into the Cu-Zr based matrix to form Cu-Zr-M ternary alloy system, as well as the third element Al and the fourth element RE(Y or Gd) will be added into it to form Cu-Zr-Al-RE quaternary alloy system. The ribbon and bulk alloy samples were produced by the single-roller rapid quenching and the spray casting in copper mold, respectively. The XRD analysis, thermodynamics analysis, micro morphologies observation and mechanical property test were done to use the D/max-3B diffractometer, Netzsch STA409PCLuxx thermodynamics analyzer, JSM5600-LV SEM, CSS-44100electronic universal testing machine and Tribo Indenter nanoindentation, respectively.With the variation of component of Cu-Zr binary alloys from the deep eutectic point Cu61.8Zr38.2, eutectic point Cu56Zr44to non-eutectic point Cu50Zr50, the thermal stability and the GFA of them weaken, as well asâ–³Tx has decreased from50K to47K and Trg has dropped from0.659to0.629, i.e., the component ratio of Cu-Zr is obviously influential in their thermal stability and the glass forming ability (GFA). The Cu50Zr50bulk metallic glasses alloy (BMGs) with4mm diameter has been obtained by the spray casting in copper mold, which possesses ofâ–³Tx with value of39K and Trg with value0.657, but the BMGs with6mm diameter has partially crystallized.With RE content increasing, the negative mixing enthalpy of Cu-Zr-RE (Y/Gd) ternary alloy system drops, the average atom radius and electron consistence of the system rises, the thermal stability varies in a narrow range and the GFA weakens. Trg of the (Cu61.8Zr38.2)1-xYx approximately linearly reduces from0.676to0.664with their negative mixing enthalpy decreasing from21.682kJ/mol to21.308kJ/mol and Trg of the (Cu56Zr44)1-xGdx shows the similar variation. With Al content increasing from2at%to4at%, the negative mixing enthalpy of the Cu62-xZr38-xAl2-x rises, the average atom radius reduces, the electron consistence rises and Trg of ribbon amorphous samples increases from0.657to0.661. Only the Cu61Zr37Al2BMGs with4mm diameter can be obtained by the spray casting in copper mold, which possesses of Trg with value0.664. It follows that the effect of Al content on the thermal stability and GFA of the Cu62-xZr38-xAl2x is dissimilar in different processings.With RE content increasing, the thermal stability and GFA of the Cu46Zr47-xAl7Yx and Cu45Zr48-xAl7Gdx quaternary alloy system appear fluctuation in a narrow range. Increasing of RE content will make the negative mixing enthalpy drop and the average atom radius of the two systems rise (size effect), the GFA of the two systems will reach to an optimal value when the negative mixing enthalpy and size effect of the systems coordinate with each other, i.e., both the negative mixing enthalpy and the size effect of the systems influence on their GFA, but the effect of the size effect on the GFA is more obvious. The forming size also evidently influences on the thermal stability, the GFA and mechanical properties of the Cu46Zr42Al7Y5BMGs, the diameter of the BMGs can be reach to6mm by the spraying cast in copper mold, but the BMGs with8mm diameter occurred crystallization and the crystallization phases were mainly composed of the Zr2Cu and Zr5Cu. Theâ–³Tx, Trg and mechanical properties of the BMGs with4mm diameter are superior to the BMGs’with6mm diameter.All ribbon amorphous alloys appear roughly similar microstructure morphology, which free surfaces and surface covered roller are uniform and dense, and some river-like veins with varying sizes and clear directions exist in the morphology of surface covered roller. The alloy components and their ratio have an evident influence on the morphology of the BMGs and all morphologies contain disorder-like distribution veins. Some micro-cracks, small amount of crystalline phases, the second phase particles or contraction cavities exist in the morphologies of the BMGs with the weaker GFA.All ribbon amorphous alloys possess a higher elastic modulus and nano hardness, the two mechanical properties decrease with the GFA weakening. Moreover, the nano hardness of (Cu61.8Zr38.2)1-xYx approximately linearly decreases with Trg lessening. The BMGs with4mm diameter appear a higher compressive strength in the compression tests and possess a higher Vickers hardness, the two mechanical properties also decrease with the GFA weakening. The BMGs occur to brittle fracture at about45°along the compression direction, the fracture surfaces are smooth and plain which possess a typical vein-like pattern and the uniformly distribution veins are corresponding to the direction of shear zone, indicating the fracture of the BMGs is a pure shear deformation in the slip plane.Finally, the relationship among the negative mixing enthalpyâ†'the GFAâ†'the mechanical properties (nano-hardness) of the Cu-Zr-Re ternary amorphous alloys has been indirectly built in this paper, i.e., the decreasing of the negative mixing enthalpy of the system will make the GFA weaken and the weakening of the GFA will make the mechanical properties drop.