【作者】 王媛媛；

【导师】 王爱民； 朱正旺；

【作者基本信息】 中国科学技术大学 ， 材料学， 2023， 博士

【摘要】 非晶合金由于高硬度、高弹性极限和高比强度等优异的力学性能,使其在工程结构材料领域中具有广阔应用前景。非晶合金的应用受限于其有限的临界铸造尺寸。由于非晶合金在热力学上处于亚稳态,因此提高非晶合金的热稳定性和延缓晶化对提高非晶合金的玻璃形成能力、推动非晶合金的应用具有重要意义。本文从热力学和动力学的角度对TiZr基非晶合金玻璃形成能力、热稳定性及晶化动力学以及微合金化对该合金玻璃形成能力的影响进行了探究,主要研究内容和结果如下:对Ti32.8Zr30.2Cu9Ni5.3Be22.7合金玻璃形成能力及其机理进行了探讨。结果表明,Ti32.8Zr30.2Cu9Ni5.3Be22.7合金的晶化驱动力ΔGl-x仅为1.6 kJ/mol,脆性指数为D*=45.2,属于具有超高玻璃形成能力的块体非晶合金。由于Ti32.8Zr30.2Cu9Ni5.3Be22.7合金的过冷液体中存在较强的中短程有序结构,说明超高的玻璃形成能力是热力学和动力学协同作用的结果。通过Angell脆性概念和动力学方程对其过冷液体和高温熔体的动力学行为分析发现,Ti32.8Zr30.2Cu9Ni5.3Be22.7合金存在“脆-强”结构转变。在Ti32.8Zr30.2M14.3Be22.7合金的基础上通过改变添加元素的种类和比例,用几乎相同原子尺寸的Cu元素、Fe元素、Co元素和Ni元素相互替换,形成Ti32.8Zr30.2Cu9M5.3Be22.7(M=Fe、Co、Ni)、Ti32.8Zr30.2Fe9M5.3Be22.7(M=Co、Ni、Cu)和Ti32.8Zr30.2(FeCoNiCu)14.3Be22.7系列合金,以此探究微合金化对非晶合金玻璃形成能力的影响。结果表明,微合金化不仅能够提高Ti32.8Zr30.2M14.3Be22.7系列合金中晶态相形核和长大需要克服的能垒,使晶态相形核和长大的过程更加困难,也能够提高组成元素原子之间的结合力,使合金具有相对稳定的过冷液相。在Ti32.8Zr30.2Cu9Ni5.3Be22.7合金的基础上通过调节Ti元素和Zr元素的原子比例获得了 Ti63-xZrxCu9Ni5.3Be22.7系列合金。采用热力学和晶化动力学探索了Ti63-xZrxCu9Ni5.3Be22.7系列合金的非晶形成能力。结果表明,当Ti元素和Zr元素的原子比无限接近1:1时,该系列合金的晶化激活能Ex和Ep的数值达到最大值,且高于玻璃转变激活能Eg。所以当合金中Ti元素和Zr元素的原子比无限接近1:1时,该系列非晶合金具有最优异的玻璃形成能力。特征温度参数与升温速率的正相关趋势,表明Ti63-xZrxCu9Ni5.3Be22.7合金玻璃转变及晶化过程均受到升温速率的影响,显示出明显的动力学特性。通过对Ti32.8Zr30.2Cu9Ni5.3Be22.7合金进行后处理(退火处理),探究后处理对Ti32.8Zr30.2Cu9Ni5.3Be22.7合金玻璃转变和力学性能的影响,研究了铸态和退火处理后合金的热稳定性和晶化动力学之间的内在关系。结果表明,对Ti32.8Zr30.2Cu9Ni5.3Be22.7合金进行热处理后,其热力学稳定性明显增强。说明退火处理能够提高非晶合金热力学稳定性。晶化动力学方面,Ti32.8Zr30.2Cu9Ni5.3Be22.7合金进行退火处理后,玻璃转变激活能明显降低,且随着退火时间的增长而逐渐升高,说明不同的退火处理条件可以导致不同的玻璃转变变化。力学性能方面,Ti32.8Zr30.2Cu9Ni5.3Be22.7合金的抗压强度随着退火时间的增加而提高。同时弹性模量、杨氏模量和剪切模量也有不同程度的提高,其中弹性模量的升幅达到了 1.2%,剪切模量的升幅达到了 7.6%,杨氏模量的升幅达到了 7%。特征温度参数与升温速率的正相关趋势表明,铸态和退火后的Ti32.8Zr30.2Cu9Ni5.3Be22.7合金玻璃转变和晶化的过程均受到升温速率的影响,显示出明显的动力学特性。更多还原

【Abstract】 Amorphous alloys have been widely noticed in the field of engineering structural materials with promising applications due to their excellent mechanical properties such as high hardness,high elastic limit and high specific strength,which are limited by their critical casting dimensions.Amorphous alloys are thermodynamically substable,so it is important to improve the thermal stability and retard the crystallization rate of amorphous alloys to promote the application of amorphous alloys.In this paper,the glass formation ability,thermal stability and crystallization kinetics of TiZr-based alloy are investigated by thermodynamic and kinetic methods.In this paper,Ti32.8Zr30.2Cu9Ni5.3Be22.7 alloy is used as the basis,and different alloy systems are formed by adjusting the types and proportions of added elements.The bulk alloy specimens were prepared by the copper mold casting method.The structure and properties of the alloy specimens were characterized by X-ray diffractometer,Differential Scanning Calorimetry,Transmission Electron Microscope and universal mechanical testing machine,respectively.The research content and the results obtained of this paper include:The glass forming ability of Ti32.8Zr30.2Cu9Ni5.3Be22.7 alloy and its mechanism were investigated.The results show that the crystallization driving force ΔGl-x of Ti32.8Zr30.2Cu9Ni5.3Be22.7 alloy is only 1.6 kJ/mol and the brittleness index is D*=45.2,which is an amorphous alloy with ultra-high glass-forming ability.The presence of a strong short-and medium-range ordered structure in the supercooled liquid of the alloy indicates that the ultra-high glass-forming ability is the result of the synergistic effect of thermodynamics and kinetics.The kinetic behavior of the supercooled liquid phase and the high-temperature melt was analyzed by the Angell brittleness concept and the kinetic equations,which revealed the existence of a "fragile-strong"transition in the alloy.Based on the Ti32.8Zr30.2M14.3Be22.7 alloy,the Ti32.8Zr30.2Cu9M5.3Be22.7(M=Fe,Co,Ni),Ti32.8Zr30.2Fe9M5.3Be22.7(M=Co、Ni、Cu)and Ti32.8Zr30.2(FeCoNiCu)14.3Be22,7 series alloys were formed by changing the type and proportion of added elements and replacing each other with Cu,Fe,Co and Ni elements of almost the same atomic size.The effect of microalloying on the glass forming ability of amorphous alloy was investigated.The results show that microalloying can not only increase the energy barriers that need to be overcome for the nucleation and growth of the crystalline phase in Ti32.8Zr30.2M14.3Be22.7 alloys,making the process of nucleation and growth of the crystalline phase more difficult,but also improve the bonding force between the atoms of the constituent elements and give the alloy a relatively stable supercooled liquid phase.The Ti63-xZrxCu9Ni5.3Be22.7 series alloy compositions were obtained by adjusting the atomic ratios of Ti and Zr elements on the basis of Ti32.8Zr30.2Cu9Ni5.3Be22.7 alloy.The glass forming ability of Ti63-xZrxCu9Ni5.3Be22.7 series alloys was explored using thermodynamics and crystallization kinetics.The results show that when the atomic ratio of Ti and Zr elements is infinitely close to 1:1,the values of crystallization activation energy Ex and Ep of this series of alloys reach the maximum and are higher than the glass transition activation energy Eg.Therefore,when the atomic ratio of Ti and Zr elements in the alloy is infinitely close to 1:1,this series of amorphous alloys has the most excellent glass formation ability.The characteristic temperature parameters and the heating rate basically show a positive correlation trend,indicating that the glass transition and crystallization processes of Ti63-xZrxCu9Ni5.3Be22.7 alloys are affected by the heating rate and show obvious kinetic characteristics.The effect of post-treatment on the glass transition and mechanical properties of Ti32.8Zr30.2Cu9Ni5.3Be22.7 alloy was investigated by annealing treatment.The intrinsic relationships between the thermal stability and crystallization kinetics of the as-cast alloy and the alloy after the annealing treatments were investigated.The results show that the thermomechanical stability of Ti32.8Zr30.2Cu9Ni5.3Be22.7 alloy is significantly enhanced after heat treatment,indicating that annealing treatment can improve the thermomechanical stability of amorphous alloys.As for the crystallization kinetics,the glass transition activation energy of Ti32.8Zr30.2Cu9Ni5.3Be22.7 alloy was significantly reduced after annealing and gradually increased with the increase of annealing time,indicating that different annealing treatment conditions can lead to different glass transition changes.As for the mechanical properties,the compressive strength of Ti32.8Zr30.2Cu9Ni5.3Be22.7 alloy increased with the increase of annealing time.The elastic modulus,Young’s modulus and shear modulus also increased to different degrees,with the increase of elastic modulus reaching 1.2%,shear modulus reaching 7.6%and Young’s modulus reaching 7%.The trend of positive correlation between the characteristic temperature parameters and the heating rate indicates that the glass transformation and crystallization processes of both as-cast and annealed Ti32.8Zr30.2Cu9Ni5.3Be22.7 alloys are influenced by the heating rate,showing obvious kinetic properties.更多还原