【作者】 姜清奎；

【导师】 蒋建中；

【作者基本信息】 浙江大学 ， 材料学， 2012， 博士

【摘要】 大块金属玻璃具有高硬度、高弹极限等特性,显示出广泛的应用前景。强玻璃形成能力的合金体系的开发成为金属玻璃研究的核心内容之一,这不仅关系着金属玻璃能否得到广泛的商业应用,还直接影响人们对于金属玻璃形成机理的认识。本论文在LaAlCu合金体系基础上,通过加入与主元具有类似化学性质或相近原子尺寸的化学元素Ag、Ni、Co元素,通过成分优化,开发出一系列临界尺寸在20～30 mm的La-Al-(Cu, Ag)-(Ni, Co)大块金属玻璃。最强的玻璃形成能力组分为La65Al14(Cu5/6Ag1/6)11(Ni1/2Co1/2)10,其临界尺寸超过35mm,是目前世界上尺寸最大的稀土基金属玻璃。从结构、热力学、动力学因素角度研究发现La-Al-(Cu, Ag)-(Ni,Co)合金晶相和过冷液相之间较小的吉布斯自由能差是其强玻璃形成能力的关键因素。通过高温原位X射线衍射研究La62A114Cu11.7Ag2.3Ni5Co5在玻璃态、过冷液态及液态的局域原子结构差异。发现其最近邻壳层的配位数为15.1±0.1,并且不依赖于温度而变化,而合金La62A114Cu24和La62A114Cu20Ag4的配位数却随着温度上升略有下降。研究La基金属玻璃的室温纳米压痕变形行为时发现,在室温时其变形模式的转变趋势如下：首先从极低加载速率时的Homo-Ⅰ变形模式转变到中度加载速率时的Inhomo变形,然后再到高加载速率时的Homo-Ⅱ变形模式,基于剪切转变区模型(STZ)提出了加载速率对La基大块金属玻璃的塑性变形模式的影响机制。发现离子注入技术在不影响玻璃形成能力的同时可以作为提高金属玻璃耐腐蚀性的一种有效途径,并在La基金属玻璃上进行了验证。合金耐腐蚀性的提高主要可归因于含Nb(约100 nm)表面层的强钝化能力。针对La基合金力学性能及热稳定性较差的弱点,尝试开发了一种具有优异综合力学性能且具有强玻璃形成能力的体系。选择CuZr基合金,在ZrCuAl合金基础上,采用加入与主元具有类似化学性质的Ag元素,并通过成分优化,成功开发出一系列临界尺寸超过20mm的Zr-(Cu,Ag)-Al金属玻璃,发现其在很大的成分范围内可直接熔炼成约25g左右的非晶锭子。从结构、热力学、动力学角度研究发现Ag元素添加后,局域原子更紧密的堆垛以及晶态相与过冷液相之间更小的吉布斯自由能差成为其具有强玻璃形成能力的关键因素。最后,采用原位TEM技术在NiNb金属玻璃非晶薄膜中首次发现了6.6%弹性极限及40%的拉伸超塑性变形的存在,基于热膨胀、自由体积模型、杨氏模量、尺寸效应、外部约束(confinement)等因素考虑,对其弹性及塑性变形机理进行了分析。更多还原

【Abstract】 Bulk metallic glasses (BMGs) have excellent properties, such as high hardness, high elastic strain limit, etc., which make them, promising for industrial applications. Hence, searching BMG compositions with high glass forming ability (GFA) is one of the most important issues of BMGs since it is not only closely related to their pratical applications but also the understanding of the mechanism for their high GFA.In this thesis, starting from ternary LaAlCu alloy system, we developed a series of La-Al-(Cu, Ag)-(Ni, Co) BMGs with critical sizes over 20-30 mm, in which the best glass former is La65Al14(Cu5/6Ag1/6)11(Ni1/2Co1/2)10 with critical size over 35mm by optimizing the compositions with elements of Ag, Ni and Co that have similar chemical properties and atomic radius to the main component. So far, it is still the largest Re-based BMG reported in the world. From the structure, thermodynamics and kinetics consideration, it was found that the crucial factor contributing to the high GFA is the lower Gibbs free energy difference between the crystalline and the supercooled liquid phase.The local structure difference in the glassy, the supercooled liquid and the liquid state of La62Al14Cu11.7Ag2.3Ni5Co5 BMG was studied by using in situ high temperature X-ray diffraction. It was found that the coordination number is of about 15.1±0.1, being independent on the temperature, while it slightly decreases for La62Al14Cu24 and La62Al14Cu2oAg4 BMGs with temperature uprising.Room temperature deformation behavior of the La62Al14(Cu5/6Ag1/6)14(Ni0.5Co0.5)10 BMG was studied using nanoindentation at different loading rates. A trend for the deformation mode variation was suggestioned to be:from homogeneous deformation I region at extremely low loading rates to inhomogeneous deformation at middle loading rates and finally to homogeneous deformation II at extremely high loading rates. The mechanism of loading-rate dependent plastic deformation behavior for La-based BMGs was proposed based on the shear transformation zone (STZ) model.Subsequently, we discovered that the ion-implantation technique can be applied to improve the corrosion resistance of BMGs without damage to their GFA. This idea was proven to be true on the La62Al14(Cu5/6Ag1/6)14(Ni0.5Co0.5)10 BMG. BMG. The improvement of corrosion resistance for the implanted alloys is attributed to the high passivating ability of the Nb-containing surface layer (about 100 nm thick).To overcome the poor mechanical properties and thermal stability of La-based BMGs, we attempted to develop an alloy system simultaneously exhibiting excellent mechanical properties and GFA. Here, selecting CuZr-based alloy and adding Ag in ZrCuAl ternary alloys, fully BMGs with at least 20 mm in diameter and some even about 25 gram amorphous metallic ingots can be prepared in a wide Zr-(Cu,Ag)-Al composition range The origin of high GFA in the studied system is attributed to the denser local atomic packing and the smaller difference in Gibbs free energy between supercooled liquid and crystalline phases after Ag addition. (for Zr46(Cu4.5/5.5Ag1/5.5)46Al8,⊿Gtl-s=1.5 kJ/mol).Last but not least, we experimentally revealed 6.6% elastic strain limit and 40% tensile plasticity for monolithic NiNb metallic glass films confined by frames by in situ high resolution transimission electron microscopy (HRTEM) observations. The origin of the high tensile elastic limit and plasticity was analyzed from the factors of thermal expansion, free volume model, Young’s modulus, size effect and frame confinement, etc.更多还原