Study On The Effects Of Microalloying On The Glass Forming Ability, Thermal Stability And Mechanical Properties Of Cu-based Bulk Metallic Glasses

Research on improving the glass forming ability (GFA) and properties of Cu-based amorphous alloys has become one of the most attractive fields due to their low price and high mechanical performance.In this paper, GFA of Cu60Zr30Ti10 alloy and the mechanical properties of (Cu60Zr30Ti10)98Y2 bulk metallic glass were increased by minor addition of elements.(Cu60Zr30Ti10)98Y2, (Cu60Zr30Ti10)97Y2Al1 and (Cu60Zr30Ti10)96Y2Ni2 amorphous alloys with diameters of 4 mm were prepared successfully by copper mould cooling and injection-casting with low purity raw materials.The effects of microalloying on the glass forming ability(GFA),thermal stability and the mechanical properties of Cu60Zr30Ti10, (Cu60Zr30Ti10)98Y2 alloys have been investigated by XRD, DSC,SEM, microhardness and QJYL et al.And the effect of crystallization on the mechanical properties of (Cu60Zr30Ti10)98Y2 bulk metallic glass during continuous heating and isothermal annealing process were studied.Results show that the GFA of Cu60Zr30Ti10 alloy was increased by adding Y, Sn. Ag element, especially for Y element.Meanwhile Y improved the thermal stability of the basic system. However. GFA of (Cu60Zr30Ti10)98Y2 alloy was more or less decreased by adding Al,Ni,Si element, and the effect of adding 1 at.% Al or 2 at.% Ni is smaller. But 1 at.%Al can obviously improve the thermal stability.Crystallization in amorphous alloys, including that occurs during solidification or during annealing treatment, has a big impact on the properties of these alloys.The mechanical property of (Cu60Zr30Ti10)98Y2 bulk amorphous alloy is better than the partial crystallization alloys (Cu60Zr30Ti10, (Cu60Zr30Ti10)98M2 (M=Sn, Ag))from casting, its compressive strength reaches to 1610MPa. The appearance of vein-like patterns reveals that local plastic deformation happens.Partial crystallization occured in (Cu60Zr30Ti10)98Y2 bulk amorphous alloy during the isothermal annealing process at 623 K(below Tg)for 30min. and compressive strength increased to 1710MPa from 1610MPa for micro crystallization.After the isothermal annealing above Tg (723K×30min.753K×30min.773K×30min).obvious crystallization occurred in (Cu60Zr30Ti10)98Y2 bulk metallic glass.And with the annealing temperature increasing. the crystallization increases, cellular precipitated phases change into dendritic phases, the mechanical properties decreases, the feature of fracture morphology changes to brittle fracture.Microalloying is a useful method for improving the mechanical performance of bulk metallic glasses.Mechanical properties of bulk amorphous alloys increase to 1750MPa and 1770MPa respectively by adding 1 at.% Al and 2 at.%Ni,and Al also improves the plasticity.The apparent activation energies calculated by Kissinger and Ozawa functions show that crystallizations of (Cu60Zr30Ti10)98Y2, Cu60Zr30Ti10)97Y2Al1 and (Cu60Zr30Ti10)96Y2Ni2 amorphous alloys were processed by three steps, and apparent activation energies increase with temperature, that is Ep1