【作者】 潘红雄；

【导师】 胡锐；

【作者基本信息】 西北工业大学 ， 材料学， 2007， 硕士

【摘要】 本文以Ti₄₀Zr₂₅Ni₈Cu₉Be₁₈非晶合金为研究对象，利用DSC、XRD、热膨胀仪、电子万能试验机、SEM、TEM等手段系统研究了钛基非晶合金的结构弛豫和晶化行为，探讨了不同温度压缩载荷作用下的力学性质和变形破坏机制，主要研究内容和结论如下： 利用DSC、XRD等技术研究了Ti₄₀Zr₂₅Ni₈Cu₉Be₁₈非晶合金的晶化行为。其中，连续升温过程的晶化动力学分析表明，Ti₄₀Zr₂₅Ni₈Cu₉Be₁₈非晶薄带在各个特征温度下的激活能E_g、E_x1和E_p1分别为384，228，306KJ／mol，均高于块体非晶合金相应的激活能，说明其热稳定性强烈地依赖于玻璃转变过程中的冷却速率，快凝薄带的热稳定性高于块体合金。 利用热膨胀仪分析了Ti₄₀Zr₂₅Ni₈Cu₉Be₁₈非晶合金的结构弛豫和晶化特征，测得其晶化前的平均膨胀系数为α=9.89x10^-6K^-1，随着晶化过程的进行，膨胀系数急剧降低。结合晶化行为的研究，认为Ti₄₀Zr₂₅Ni₈Cu₉Be₁₈非晶合金在升温过程中存在三级晶化过程，一级晶化为纳米准晶从非晶基体中的析出和长大过程，二级晶化对应着Laves相从残余非晶基体和初生准晶相中的析出过程。Ti₄₀Zr₂₅Ni₈Cu₉Be₁₈非晶合金在643K等温晶化的Avrami因子n（x）值在1～4之间，等温初期n（x）=1～2.5，表明准晶相的形核和长大主要为扩散控制的一维生长方式，后期n（x）=2.5～（?），表明析出相的生长方式为扩散控制的三维生长。 Ti₄₀Zr₂₅Ni₈Cu₉Be₁₈块体非晶合金室温（293K）压缩载荷作用下表现出较好的塑性，且随着应变速率的降低塑性增大，抗压强度σ_bc，可达1990MPa左右，压缩断面呈典型的脉络状花样，试样侧面出现许多与断面相垂直且相互平行的剪切带：在初始晶化阶段由于纳米准晶的析出导致其显微硬度显著提高，但随着准晶相的长大和Laves相的析出，非晶合金的显微硬度和压缩断裂强度迅速下降。 低温（77K）下Ti₄0Zr₂₅Ni₈Cu₉Be₁₈块体非晶合金的抗压强度有所提高，达2223MPa，但由于低温抑制了剪切带的扩展，断裂前没有表现出宏观塑性，断面脉络状花样大幅度减少。在过冷液相区（601K和621K）Ti₄₀Zr₂₅Ni₈Cu₉Be₁₈块体非晶合金塑性可达40％以上，且随着应变速率的减小，屈服极限由987MPa下降到760MPa，表明该合金具有较好的热加工潜力。更多还原

【Abstract】 Bulk metallic glass have been developed in many alloy systems and show many unique properties associated with atomic structure, such as high yield strength, large elastic limit, corrosion resistance, and so on. Recently, development of Ti-based bulk metallic glass with lower density and higher specific strength is expected to expand the possible application fields. In this paper, the structural relaxation and crystallization behavior of Ti₄₀Zr₂₅Ni₈Cu₉Be₁₈ amorphous alloy, due to its higher glass forming ability and mechanical properties, are investagited by differential scanning calorimetry （DSC）, X-ray diffraction （XRD）, thermal dilatometer and transmission electron microscopy （TEM）. In addition, the compressive deformation and fracture mechanism of Ti₄₀Zr₂₅Ni₈Cu₉Be₁₈ bulk amorphous alloy over wider temperature region （77-621K） and strain rates are explored in detail.In the paper, the effects of relaxation and crystallization process on the stability of metallic glass in supercooled liquid region have been studied. Under continuous heating conditions, the activation energies for the glass transition and crystallization at the onset and first peak crystallization temperatures of Ti₄₀Zr₂₅Ni₈Cu₉Be₁₈ amorphous ribbons were 384, 228, 306 KJ/mol, respectively, which were higher than that in bulk metallic glass. The results indicated that the stability of metallic glass was strongly depended on the cooling rate in the glass transition process; the stability of amorphous ribbons was higher than bulk metallic glass.Crystallization kinetics research indicated that the glass transition and crystallization behavior showed the typical characteristic of kinetics. The crystallization process contained three steps of crystallization reactions corresponding to the precipitation of quasicrystalline phase on the amorphous maxtrix, the precipitation of Laves phase on the remaining amorphous maxtrix and the transition from quasicrystalline phase to Laves phase, the transition from Laves phase to an unknown phase, respectively. The average expansion coefficient was 9.89×10^-6K^-1 before crystallization, the reducing free volume led to the rapid decrease of the expansion coefficient in the crystallization process in Ti₄₀Zr₂₅Ni₈Cu₉Be₁₈ alloy.Share bands appeared at the outboad of the samples with a direction of normal and parallel to the fracture surface when tested at room tempareture and the compression更多还原