Study On Microstructure And Properties Of Zr-based Bulk Metallic Glass

Based on three empirical criteria and deep eutectic theory,the composition design of amorphous alloys[(Zr_0.72Cu_0.28)_0.88Al_0.12]_100-x00-x Ni_x?x=2,4,6,8,10,12,14 at.%?with large plasticity(Zr_0.72Cu_0.28)₈₈Al₁₂2 was carried out by adding different Ni elements.The properties and structures of these alloys were analyzed by X-ray diffraction,DSC differential thermal analyzer,room temperature compression test,microhardness test,scanning electron microscope and electrochemical workstation.The results are as follows:?1?The glass transition temperature T_g increases with the increase of cooling rate.While the reduced glass transition temperature T_rg,the supercooled liquid phase?T_x,the melting temperature T_m and the liquid temperature decrease with the increase of cooling rate with(Zr_0.72Cu_0.28)₈₈Al₁₂2 alloys;The cooling rates of(Zr_0.72Cu_0.28)₈₈Al₁₂alloys with different diameters??2,?3,?4 and?6?are significantly reduced,which are 1324.5,585.1,322 and 141.1 K·s^-1,respectively.The plastic deformation decreases significantly with the decrease of cooling rates,which are 20.2%,8.3%,2.6%of 2 mm,3 mm and 4 mm respectively,while brittle fracture occurs for 6 mm specimens;The radial element content and microhardness of(Zr_0.72Cu_0.28)₈₈Al₁₂amorphous alloys with different diameters??2,?3,?4 and?6?fluctuate obviously,which indicates that the amorphous alloys are inhomogeneous in micro-structure.?2?The?H_mixix and?S_mixix of the designed components were calculated.It was found that?H_mixix decreased with the increase of Ni content,while?S_mixix increased with the increase of Ni content,which accorded with the composition design theory.The thermal stability of[(Z_r0.72Cu_0.28)_0.88Al_0.12]_100-x00-x Ni_x?x=2,4,6,8,10,12,14 at.%?alloy varies with the content of Ni element.The supercooled liquid phase region?T_x first increases and then decreases with the increase of Ni content.At x=10,the supercooled liquid region?T_x reaches 101.1K and its thermal stability is the best;At x=14,the supercooled liquid phase region?T_x is 93.4 K,its thermal stability is relatively poor,but it is still better than(Zr_0.72Cu_0.28)₈₈Al₁₂2 alloy.At the same time,the amorphous alloy at x=10 has a large plastic deformation?_p-23.3%.?3?The pitting corrosion resistance of amorphous alloys can be improved by adding appropriate amount of Ni.The polarization curves and EIS fitting show that the pitting corrosion resistance of amorphous alloys increases first and then decreases with the increase of Ni content.The pitting resistance of amorphous alloys is the best when x equals to 10.The corrosion potential E_corr,current density I_corrorr and electron transfer impedance R_ctt are-0.699 V,1.254×10^-77 A/cm² and 5695?·cm²,respectively,which has the best corrosion resistance.?4?Thenon-isothermalcrystallizationof[(Zr_0.72Cu_0.28)_0.88Al_0.12)₉₀]Ni₁₀amorphous alloys shows that the characteristic temperature moves to the high temperature with the increase of the heating rate;The ideal glass transition temperature T₀ was 524.6 K by VFT equation fitting;The glass transition activation energy E_g,the initial activation energy E_x and peak activation energy E_P were calculated by the Kissger equation,which were 128.6,310.4 and 282.4 KJ/mol,respectively.while the Ozawa equation yielded 139.8,323.1 and 295.0 KJ/mol,respectively.It is found that the initial activation energy E_x are larger,which indicates that the crystallization of metallic glass is more difficult and the glass performance is stable,the crystallization volume fraction diagrams at different heating rates is"S"shape,and the Avrami exponent n?a?is between 1.67 and 7.81,which indicates that the growth type of alloy during non-isothermal crystallization is controlled by interface.?5?The isothermal crystallization in supercooled liquid region of amorphous alloy[(Zr_0.72Cu_0.28)_0.88Al_0.12)₉₀]Ni₁₀0 shows that the lower the isothermal temperature,the longer the incubation period correspondingly;The crystallization volume fraction diagrams at different isothermal temperatures show a single"S"shape,and the lower the isothermal temperature,the flater the crystallization volume fraction diagram;The variation of local activation energy of[(Zr_0.72Cu_0.28)_0.88Al_0.12)₉₀]Ni₁₀0 with the volume fraction of crystallization during the whole isothermal crystallization process.The value of isothermal Avrami exponent n?a?of[(Zr_0.72Cu_0.28)_0.88Al_0.12)₉₀]Ni₁₀0 ranges from 1.2 to 11.74,which indicates that the isothermal crystallization is a crystallization process controlled by the interface with different nucleation rates and growth dimension.