【作者】 洪凯；

【导师】 张博；

【作者基本信息】 合肥工业大学 ， 材料工程（专业学位）， 2018， 硕士

【摘要】 非晶合金中变形与弛豫行为密切相关,两者是当前非晶材料学科的研究热点。Cu-Zr二元非晶体系由于其简单的化学成分与优异的力学性能,已经成为非晶研究中理想的模型材料之一。本文以经典的二元非晶合金Cu₅₀Zr₅₀和Cu₆₀Zr₄₀薄带为研究对象,通过动态力学分析仪（DMA）系统研究应力和温度对其接近玻璃转变温度（T_g）下单轴拉伸蠕变性能的影响。在相同升温速率下分别采用差式扫描热分析与动态力学分析测得其玻璃转变温度。利用阿伦尼乌斯关系得到Cu₅₀Zr₅₀和Cu₆₀Zr₄₀非晶带材蠕变表观激活能分别为5.3 eV和6.2 eV,表明Cu-Zr非晶合金的拉伸蠕变变形与玻璃转变（α弛豫）相关。计算出蠕变应力指数n,发现n随着温度的升高而减小并接近1,结果表明Cu₅₀Zr₅₀和Cu₆₀Zr₄₀非晶在接近玻璃转变温度时蠕变变形趋向于牛顿粘性流动。为了进一步探究激活能随温度的变化关系,测量了Cu₅₀Zr₅₀非晶合金从室温到玻璃转变温度下的蠕变激活能。不同应力下的激活能温度谱表现出相同的趋势,在低温时较低并随着温度升高而增大,在玻璃转变温度附近出现峰值。为了进一步研究Cu-Zr非晶合金中蠕变与弛豫行为的关系,通过动态力学测量不同频率下拉伸的损耗模量-温度曲线。测得β弛豫的激活能为（129±6.5）kJ/mol,与蠕变激活能转变阶段对应。此外,还测量了Cu₅₀Zr₅₀高温的应力松弛行为,通过KWW方程拟合,系统研究了温度、初始应变和循环次数的影响。研究发现弛豫因子β随温度升高而升高;而当初始应变和循环次数增大时,弛豫因子β减小,初始应力和松弛时间增大,这表明非晶内部流变单元变多,结构更加复杂。更多还原

【Abstract】 The deformation behaviour of metallic glass is closely related to the relaxation behaviour which are both current research hotspots in amorphous materials science.Cu-Zr binary metallic glass system has become one of an ideal model material because of its simple chemical component and excellent mechanical properties.In this work,Cu₅₀Zr₅₀ and Cu₆₀Zr₄₀ binary metallic glasses ribbons have been systematically studied by uniaxial tensile creep at temperature close to the T_g（glass transition temperature）via DMA（Dynamic Mechanical Analyzer）.The T_g was measured by DSC（Differential Scanning Calorimeter）and DMA under same heating rate respectively.The creep apparent activation energies obtained from Arrhenius equation for Cu₅₀Zr₅₀ and Cu₆₀Zr₄₀ are 5.3 eV and6.2 eV respectively,it indicates that the tensile creep deformation in Cu-Zr metallic glass is related to the glass transition（α-relaxation）behavior.Creep stress exponent decreases to¹ with the increasing temperature,this result shows Cu₅₀Zr₅₀ and Cu₆₀Zr₄₀ metallic glasses tend to be Newtonian viscous flow when it approaches to glass transition stage.To futher investiagate the temperature dependence on activation energy,we calculated the activation energy of creep（Q_c）over a broad temperature range from room temperature（RT）to glass transition temperature（T_g）for Cu₅₀Zr₅₀ metallic glass.It is found that the activation energy spectra in different stress show similar tendencies,dramatically low at low temperatures,rise at sub-T_g temperatures and peaking around T_g.To further investigate the correlation between creep and relaxation behavior in Cu-Zr metallic glass,dynamic mechanical measurements were conducted to acquire loss modulus-temperatures curves with varying frequency in tensile model.The activation energy for secondary（β）relaxation,E_β,was measured to be（129±6.5）kJ/mol,which corresponds to the transitional stage energy value in Q_c.Besides,Cu₅₀Zr₅₀ metallic glass ribbons have been studied by uniaxial tensile stress relaxation at temperature close to the T_g.The temperature,initial strain and cycle index dependences on stress relaxation were systematically discussed by KWW model.It was found that relaxation exponentβdecreases with increased temperature.When initial strain and cycle index increase,relaxation exponentβdecreases,initial stress and relaxation time increase,the results show that the content of flow units grow in number with complicated structures.更多还原