Preparation And Superplastic Deformation Of Hf-based Amorphous Alloy

Hf-based amorphous alloy has excellent mechanical properties such as high toughness,high strength,high wear resistance and high corrosion resistance.However,its glass forming ability is poor,making it difficult to prepare large-sized amorphous alloys;Its poor plasticity at room temperature makes it difficult to process;it limits the widespread use of Hf-based amorphous alloys.In this paper,the glass forming ability of amorphous alloy is improved by replacing Ti,Zr,Cu and Ni elements in Hf-Be-Ti-Zr-Cu-Ni system amorphous alloy with Hf elements,and the high density and large size amorphous alloy parts are successfully prepared.In order to solve the problem of processing amorphous parts,the superplastic deformation mechanism of Hf based amorphous alloy is studied,and the influence of superplastic deformation on the structure is analyzed provide guidance for superplastic forming of amorphous parts.In the Hf-Be-Ti-Zr-Cu-Ni amorphous alloy system,the appropriate amount of Hf element is used to replace the Ti,Zr,Cu,and Ni elements,which significantly improves the Hf-Be-Ti-Zr-Cu-Ni the glass forming ability and density of the alloy.The Hf₂₈Be₁₈Ti₁₇Zr₁₇Cu_7.5Ni_12.5amorphous alloy has a diameter of 15 mm and a density of 8.5086g/cm³,and the Hf₂₉Be₁₈Ti₁₇Zr₁₇Cu₇Ni₁₂amorphous alloy has a diameter of 15 mm and a density of 8.5108 g/cm³.By calculating the difference in equivalent atomic size?,the equivalent electronegativity difference?x,and the mixing enthalpy?H_mix,the reasons for the enhanced glass-forming ability of the Hf-Be-Ti-Zr-Cu-Ni amorphous alloy was analyzed.Hf₂₈Be₁₈Ti₁₇Zr₁₇Cu_7.5Ni_12.5conical amorphous parts were prepared by vacuum induction casting,and the preparation process was analyzed.It is found that when the casting temperature is1550?and the casting time is 2 s,an amorphous conical part with good glass forming ability and full shape can be obtained.The quasi-static mechanical properties of Hf_26+2xBe₁₈Ti_18-xZr_18-xCu_7.5Ni_12.5and Hf₂₉Be₁₈Ti₁₇Zr₁₇Cu₇Ni₁₂amorphous alloys at room temperature were analyzed.The results show the increase of Hf content is beneficial to increase the compressive strength of the amorphous alloy.The compressive strength of Hf₂₈Be₁₈Ti₁₇Zr₁₇Cu_7.5Ni_12.5amorphous alloy will reaches 1935 MPa.Hf₂₉Be₁₈Ti₁₇Zr₁₇Cu₇Ni₁₂amorphous alloy has obvious sawtooth rheological behavior,showing a certain room-temperature plasticity,plastic deformation of 0.5%,and it also has a large yield strength of 2021 MPa,specific strength of 2.4127×10⁵N·m/kg and compressive strength of 2051 MPa.Analysis of the dynamic mechanical properties of Hf₂₈Be₁₈Ti₁₇Zr₁₇Cu_7.5Ni_12.5amorphous alloy shows that:Under dynamic load with a strain rate of 550 s^-1-1450 s^-1,the maximum fracture strength of the alloy is 1484.2 MPa,which is far lower than the fracture strength under static load 1935 MPa.The yield of amorphous alloys occurs at high strain rates,and the yield strength gradually decreases as the strain rate increases.The research on the superplastic deformation of Hf₂₈Be₁₈Ti₁₇Zr₁₇Cu_7.5Ni_12.5amorphous alloy found that the amorphous alloy showed different deformation states at different deformation temperatures and strain rates.The alloy is prone to brittle fracture when the deformation temperature is 648 K-658 K and the strain rate is 5×10^-3s^-1or more during superplastic processing.When the deformation temperature increases or the strain rate decreases,the deformation mode of the amorphous alloy gradually changes from unsteady state rheology to steady state rheology.When the deformation temperature reaches 688 K and the strain rate reaches 5×10^-4s^-1,the alloy undergoes deformation strengthening.Analysis on the microstructure and thermodynamic properties of Hf₂₈Be₁₈Ti₁₇Zr₁₇Cu_7.5Ni_12.5amorphous alloy before and after superplastic deformation.As the deformation temperature increases and the strain rate decreases,the supercooled liquid phase interval?T_xand exothermic enthalpy?H of the alloy decrease,and the tendency of the transition from amorphous to crystalline increases.When the deformation temperature is 688K and the strain rate is 5×10^-4s^-1,the alloy was crystallized.Based on the analysis results of superplastic deformation and microstructure and properties of Hf₂₈Be₁₈Ti₁₇Zr₁₇Cu_7.5Ni_12.5amorphous alloy,the processing range of superplastic forming was determined:Deformation temperature is greater than 668 K,strain rate is less than 5×10^-3s^-1.