Effect Of Mold Materials On Properties Of Zr-based Bulk Amorphous Alloy And Casting Process Study

In this thesis,the casting experiment of Zr_41.2Ti_13.8Cu_12.5Ni₁₀Be_22.5 bulk amorphous alloy is carried out by gravity casting with a self-designed fluidity test system.The influence of mold materials on the flow behavior of Zr-based bulk amorphous alloy melt is studied by changing mold materials(refractory steel,pure graphite and copper).X-ray diffractometer,differential thermal scanning calorimetry analyzer and transmission electron microscope are used to analyze the influence of casting materials on the microstructure of Zr-based bulk amorphous alloys.The compressive mechanical properties of samples with different molds are tested by universal mechanical testing machine,and combined with microstructure analysis,the effect of materials on the compressive ductility of Zr-based bulk amorphous alloys is analyzed.The thermal stability of casting samples with different molds is studied by non-isothermal method.Based on the thermal balance theory,the flow length model of the Zr-based bulk amorphous alloy melt is constructed.Through the comparison of theoretical calculation and measured flow length,the flow behavior of Zr-based bulk amorphous alloy melt is analyzed quantitatively and qualitatively.According to the measured flow length and flow length model,the heat transfer coefficients of Zr_41.2Ti_13.8Cu_12.5Ni₁₀Be_22.5 amorphous alloy and refractory steel,pure graphite and copper molds are obtained as 972,1393 and 1718 W·m^-2·K^-1,respectively.The measured flow length results show that the alloy melt has the longest flow length in pure graphite mold,while the flow length results calculated according to the model show that the alloy melt has the longest flow length in the refractory steel mold.It is caused by the self-lubricating effect of pure graphite material itself.The microstructure analysis results show that there is a trace of crystalline phase in the samples cast by refractory steel and pure graphite molds,while there is no crystalline phase in the samples cast by copper mold.The enthalpy changes caused by structural relaxation of samples cast by refractory steel,pure graphite and copper molds are-0.6,-2.8 and-5.3J/g,respectively,which indicates that as the cooling rate decreases,the free volume in the amorphous matrix is reduced,and the order of the atomic arrangement is enhanced.The difference in the cooling capacity of the mold is the main reason for the difference in the microstructure.The compression test results show that with the decrease of the cooling rate,the elastic strain,yield strength and compressive strength of Zr_41.2Ti_13.8Cu_12.5Ni₁₀Be_22.5 amorphous alloy do not change much,and the plastic strain gradually decreases.The plastic strains of samples cast by refractory steel,pure graphite and copper molds are 1.2%,1.7%and 2.6%,respectively.It is found through fitting that the effective size of the vein-like pattern has a linear relationship with the values of structural relaxation enthalpy and plastic strain,which indicates that when the cooling rate is low,trace crystallization phase in the amorphous alloy cannot effectively improve the amorphous alloy,and the amount of free volume is the main factor affecting the plasticity of the bulk amorphous alloy.The results of thermal stability study show that the characteristic temperatures of samples cast by different molds gradually move to the high temperature direction with the increase of the heating rate.The activation energy corresponding to the characteristic temperature has the smallest value of E_x,which indicates that the activation barrier that needs to be overcome in the nucleation process is the lowest and most likely to occur.When the heating rate is the same,the characteristic temperature of samples cast by refractory steel,pure graphite and copper molds gradually increases,the sensitivity of characteristic temperature to the heating rate gradually decreases,and the thermal stability gradually increase.The analysis results of non-isothermal crystallization mechanism show that the grain growth mold of the first crystallization peak corresponding to the grain of different casting samples is mainly three-dimensional growth controlled by diffusion,but the nucleation rate is different.Through the research on the casting forming process of ring-shaped fixture block,the process parameters such as pouring position,parting surface,casting shrinkage,process redundancy and pattern draft are determined.The results of casting experiments at different temperatures show that the optimal casting temperature of ring-shaped fixture block is 1323K,and a Zr_41.2Ti_13.8Cu_12.5Ni₁₀Be_22.5 amorphous alloy ring-shaped fixture block with clear outline and complete shape has been successfully cast under this casting temperature condition.Through the research on the casting process of 29320 spherical roller bearing inner and outer rings,the shape and the size of single side casting mold are determined to be 300×260×45 mm.Finally,a bearing inner ring with the weight of 1.8 kg and a bearing outer ring with the weight of 1.3 kg are successfully cast.