非晶态硼化物硬质防护薄膜的成分设计

Borides are a new type of hard, tough and chemical inertia thin film materials for protective purposes. The sputtering synthesis generally produces an amorphous state with large composition tolerance that facilitates materials synthesis. However, the large composition changes make the property control difficult. According to the cluster-plus-glue-atom model developed for amorphous metals, an ideal metallic glass with a high glass forming ability always satisfies the [cluster](glue atom)1 or 3 universal composition formula, where the cluster is the nearest-neighbor coordination polyhedron taken from a devitrification phase. The hardness at this specific composition also reaches a large value. In the present project, we will apply this new structural analysis method in the structural description of hard and light boride ceramic materials with complex and strong chemical bonds. The ternary boride systems, represented by B12C2Mg, AlMgB14 and B14Mg2 will be specially focused on and their characteristic clusters will be obtained. These clusters are then matched with elements with stronger binding strength than the existing ones and series of hard boride amorphous phases are thus designed. Magnetron sputtering technique will be employed to synthesize the thin films. The structure will be characterized and properties like hardness, elastic modulus and tribology parameters will be measured, to explore the composition – structure – property correlations in these boride amorphous phases and to verify the cluster-plus-glue-atom model. The success of the present project will shed lights on general guiding principles towards developing new hard protective thin films.

硼化物薄膜是新型的高硬、高韧性、化学惰性的防护材料，磁控溅射制备往往呈现非晶态，非晶态结构具有大的成分容忍度，有利于工艺制备，但也易导致性能多变难控。根据金属非晶合金中的规律，最大硬度对应于最高的非晶形成能力的成分点，而该成分点能够用[团簇](连接原子)x模型描述，其中团簇为相关晶体相中获取的代表近程有序结构特征的第一近邻配位多面体，x为位于团簇之间的连接原子个数。本项目把这个基于团簇的非晶合金设计方法首次应用于非晶陶瓷的设计，旨在获得具有较大成分容忍度的硬质非晶硼化物薄膜材料，分析B12C2Mg、AlMgB14及B14Mg2等硼化物的团簇结构特征，在此基础上，寻找具有更强结合能力的元素来替换连接原子，设计出系列三元硼碳化物理想非晶相，进而采用磁控溅射制备非晶薄膜，并表征成分、结构及性能，探讨三者间的相关联性，验证团簇模型。该项目的成功实施对于指导新型硬质防护薄膜的发展具有普适意义。

玻璃态材料存在某些形成能力高的成分点，该成分下的非晶表现出硬度、强度等性能的极值。本项目以硼化物硬质涂层为背景，通过引入描述玻璃态结构的团簇加连接原子模型，设计并用磁控溅射法制备了玻璃态薄膜，寻找高玻璃形成能力的(B,Al)-(C,Si)-M体系超硬轻质硼化物陶瓷的成分区，为获得易于制备的新硬质材料打下成分设计基础。.本项目通过大量实验，结合模型设计，获得了B（Al）-Si-M的最佳玻璃形成能力的结构单元与成分式；随后将该方法扩展到典型无机非金属化合物体系，给出了氧化物玻璃相关化合物中的类分子结构单元；最后，根据氧化物类分子结构单元理论，构造了硅酸盐玻璃的团簇式，通过解析康宁典型玻璃成分，确认了该模型具有指导成分设计的能力，并扩展到5G时代和深海用高强韧微晶玻璃。作为模型验证的一个实施例，根据团簇模型给出的硼33玻璃的理想成分式{M2O3}:{Si2O4}=7:9，以符合该成分式的硼玻璃为靶材，用磁控溅射法制备了高硼硅玻璃硬质薄膜，镀膜后的高硼硅玻璃可见光透光率最小损失仅为 2%，基本保留了原玻璃体的光学性能。相较于原高硼硅玻璃基底，镀膜后高硼硅玻璃的纳米硬度增加了1%～3%，杨氏模量增加了2%～3.5%，说明通过镀高硼硅玻璃薄膜提升了玻璃基片的力学性能。另外一个实施例为高铝玻璃的理想成分式{M2O3}16，以高铝玻璃和AI2O3为靶材，通过磁控溅射的方法，制备了AI2O3复合高铝玻璃薄膜，纳米硬度及杨氏模量分别为18GPa和142GPa，平均可见光透过率均在85%以上，另外本项目还给出了DLC薄膜和微晶玻璃的实施例。