【作者】 毕凯；

【导师】 戴起勋；

【作者基本信息】 江苏大学 ， 材料学， 2013， 博士

【摘要】 BCN是一种人工合成的新型材料,具有键长短、键共价性强等特点。理论研究表明BCN具有与氮化硼(BN)相似的六方和立方型结构,特别是立方BCN(c-BCN)的性质应介于金刚石和立方BN(c-BN)之间,既有金刚石的高硬度、高耐磨性,又有c-BN的热稳定性及化学惰性,是一种非常理想的新型耐磨保护涂层材料,具有广阔的应用前景。科学家们采用各种方法尝试合成这种新型材料。目前,对于BCN薄膜的制备研究多数都是以单晶Si或其他一些晶体材料为衬底进行的,虽然在薄膜的沉积工艺、组织结构与性能分析等方面取得了一些进展,但与实际应用相比还有较大差距。因此,从实际应用角度出发,本文在国内首次采用YG8硬质合金作为衬底材料,进行BCN薄膜的制备与性能研究。采用直流与射频磁控反应溅射法,以高纯石墨和h-BN为靶材料,在YG8硬质合金衬底上成功制备出BCN薄膜。采用划痕试验与球-盘式摩擦试验系统研究了不同常规工艺参数与基片处理措施对薄膜附着性能与摩擦学性能的影响；并采用FTIR、XRD和XPS等测试手段分析研究了薄膜的成分结构及其影响因素；还采用第一性原理方法计算模拟了B、C和N原子在WC表面与WC-Co表面的吸附特性,为研究BCN薄膜的沉积与生长,提供理论依据与参考。研究表明,氮气分压比、工作气压、射频功率、基底偏压等常规工艺参数对BCN薄膜的附着性能与摩擦学性能有影响,而沉积时间的影响不大。最佳沉积工艺参数是：氮气分压比25%,工作气压1.0Pa,射频功率200W和基底偏压-50V。总体来说,常规工艺制备的BCN薄膜的减摩与抗磨作用不明显,其中薄膜最高附着力仅为31.7N,与氮化硅对摩球间的最低摩擦系数为0.32,最低磨损率为2.94x10-6mm3/Nm.研究表明,基片表面预处理和沉积中间层等基片处理措施对BCN薄膜的附着性能与摩擦学性能影响较大。最佳基片处理措施分别为金刚石研磨膏研磨+酸浸蚀两步法基片表面预处理和沉积单层TiN中间层,对应BCN薄膜的附着力较高分别为37.1与48.7N,与氮化硅对摩球间的摩擦系数分别为0.07与0.14,磨损率分别为0.88×10-6与1.81x10-6mm3/Nm,具有明显的减摩与抗磨作用。FTIR分析表明,BCN薄膜中各元素均实现了原子间成键,薄膜主要为B、C、N元素的三元化合物,而不是石墨和六方氮化硼的简单混合物。对硬质合金基底表面采用金刚石研磨膏研磨+酸浸蚀预处理以及渗硼预处理均有利于B、C、N原子间的相互作用成键,有助于B、C、N元素之间成键几率的提高。XRD分析表明,BCN薄膜均以非晶态结构为主。少数薄膜中开始形成一定的晶体结构,但因其数量太少无法确定。各种基片处理措施均有利于BCN薄膜的晶化。其中,渗硼预处理还使B元素与硬质合金衬底表层的Co、W元素反应形成化合物,并形成相关的晶相。XPS分析表明,BCN薄膜中B、C和N原子不是以自由原子态存在于薄膜中,而是彼此相互作用形成了C-N、B-N与B-C等化学键,但薄膜中N、B元素的含量偏少,特别是B元素的含量明显偏少,N/C比偏低,远小于合成BC2N的要求。薄膜应该是多晶或非晶结构材料。基底表面进行金刚石研磨膏研磨+酸浸蚀两步预处理有助于提高BCN薄膜中C==N键的数量。计算表明,B、C、N原子在WC(001)与WC(100)两种表面的高对称吸附位上都能形成化学吸附：在WC(001)表面吸附时,B、N原子倾向于转移到心位HC上形成稳定化学吸附,C原子则倾向于转移到空位HO上形成稳定化学吸附；在WC(100)表面吸附时,B、C、N原子均倾向于转移到心位HC上形成稳定化学吸附。两种表面上吸附的B、C、N原子主要都是与表层W原子相互作用,形成具有部分离子性的共价键。在相同吸附位上,两种表面都是对N原子的吸附最强,而对B原子的吸附最弱。总体上看,WC(100)表面比WC(001)表面更适合吸附B、C、N原子。计算表明,WC(100)表面掺杂Co元素形成的WC-Co表面对称性有所下降,可能的吸附位增加。B、C、N原子在WC-Co表面各吸附位上仍能形成化学吸附,B、C、N原子仍倾向于转移到心位HC上形成稳定化学吸附；吸附在WC-Co表面的B、C、N原子主要都是与表层W、Co原子相互作用,形成具有部分离子性的共价键。在相同吸附位上,WC-Co表面总是对N原子的吸附最强,对B原子的吸附最弱。这从微观角度部分解释了,为什么WC-Co硬质合金表面沉积的BCN薄膜中B元素含量偏少。计算还表明Co元素的掺杂对C、N原子在硬质合金表面的吸附有不利影响。同样从微观角度部分解释了,为什么Co元素不利于硬质合金表面相关薄膜的沉积,从而为实验提供一定的参考与指导。更多还原

【Abstract】 BCN is a new type of synthetic material with characteristic shorter bond length and higher proportion of covalent bonding. Theoretical research has demonstrated that BCN has a hexagonal and cubic structure similar to BN structure. It is noteworthy that the property of cubic BCN (c-BCN) should be in between diamond and cubic BN (c-BN):it has the high degree of hardness and wear of diamond and the thermal stability and chemical inertness of c-BN. As such, c-BCN is a new, ideal type of material for wear-resistant protective coating that potentially has wide applications. Researchers have attempted to use various methods to synthesize this new material. Most studies used single crystal Si or other crystals as substrate to make BCN film. Although progress has been made in the technique of film deposition and the analyses of its structure and performance, there is still a considerable gap between research and application. To diminish this gap, this work pioneered in China to use YG8hardmetal as substrate material to make BCN film and examine its properties.Using high purity graphite and h-BN as target material, this study succeeded in making BCN film on YG8hardmetal substrate by using DC and RF magnetron sputtering. Scratch test and ball-on-disc tribological test were used to systematically examine the effects of various conventional process parameters and treatment of the substrate on the adhesion performance and tribological properties of the film. FTIR, XRD and XPS methods were used to analyze the composition and structure of the film as well as factors that affect them. In addition, first-principles method was used to computationally simulate the adsorption characteristics of B、C and N atoms on WC and WC-Co surfaces. These studies provided the theoretical basis for studying the deposition and growth of BCN film.This research showed that the adhesion and tribological properties of BCN film are influenced by conventional process parameters including nitrogen gas partial pressure ratio, working atmospheric pressure, RF power and substrate bias, but not by the time of deposition. The optimal deposition parameters are:nitrogen gas partial pressure ratio25%, working atmospheric pressure1.OPa, RF power200W, and substrate bias-50V. In general, BCN film made with the conventional process does not have obvious antifriction effect and wear resistance, with the maximum adhesive force being only 31.7N, and the lowest friction coefficient against silicon nitride being0.32, and the lowest wear rate being2.94×10-6mm3/Nm.This study also demonstrated that the pretreatment of the substrate surface and the deposition of interlayer have relatively large effects on the adhesion performance and tribological properties of BCN film. The optimal treatment of the substrate is a two-step pretreatment of the substrate surface (grinding by diamond paste followed by acid etching) and deposition of a single-layer interlayer of TiN. The corresponding BCN films’ adhesive forces are37.1and48.7N, respectively, and the friction coefficients against silicon nitride are0.07and0.14, respectively; and the wear rate are0.88×10-6and1.81×10-6mm3/Nm, respectively. Therefore, the BCN film has a clear antifriction effect and wear-resistance, and serves as a good foundation for further studies on the application of BCN film.FTIR analysis revealed that the various elements in BCN film all form bonds with each other, resulting in the film being mainly a B, C, and N three-component compound, not the simple mixture of graphite and h-BN. The grinding by diamond paste followed by acid etching pretreatment and boronizing pretreatment of the hardmetal substrate is helpful for the formation of bonds between B, C and N atoms.XRD analysis found that BCN films are mainly in a non-crystal state. A minority of films form certain crystal structures, but the quantity is too low to measure. All the methods of treatment of the substrate help the crystallization of BCN film. Moreover, boronizing pretreatment also induces B element to form a compound and corresponding crystal phase with the Co and W elements in hardmetal surface layer.XPS analysis indicated that the B, C and N atoms do not exist as free atoms in BCN film, but instead form C-N, B-N and B-C chemical bonds. However, the relative content of N and B elements, especially B element is clearly low, resulting in low N/C, which does not meet the requirement for the formation of BC2N. The film should be a multi-crystal or non-crystal material. Pretreatment of substrate surface with grinding by diamond paste followed by acid etching helps to increase the amount of C=N bonds in BCN film.Computational analysis revealed that B, C and N atoms can form chemical adsorption at the high symmetry adsorption sites of both WC(001) and WC(100) surfaces. On WC(001) surface, B and N atoms tend to move to hollow site HC to for form a stable chemical adsorption, while the C atom tends to move to hollow site HO to form a stable chemical adsorption. On the other hand, on WC(100) surface, B, C and N atoms all tend to move to hollow site HC to for form stable chemical adsorptions. On both surfaces, B, C and N atoms mainly interact with the surface W atoms to form partially ionic covalent bonds. At the same adsorption site on both surfaces, the adsorption of N atom is the strongest, and that of B atom the weakest. WC(100) is generally more suitable than WC(001) for the adsorption of B, C and N atoms.Computational analysis also revealed that WC-Co surface formed by adding Co element to WC(100) has a reduced symmetry which increases potential adsorption sites. B, C and N atoms can still form chemical adsorption on the adsorptions sites on WC-Co surface, and they still tend to move to hollow site HC site to for stable chemical adsorption. B, C and N atoms on WC-Co surface mainly interact with the surface W and Co atoms to form partially ionic covalent bonds. At the same adsorption site on WC-Co surface, the adsorption of N atom is the strongest, and that of B atom the weakest. From a microcosmic perspective, this partially explains why the content of B element is relatively low in BCN film deposited on WC-Co surface. It was also shown that addition of Co element is harmful to the adsorption of C and N atoms on hardmetal surface, which from a microcosmic perspective, partially explains why Co element is not helpful to the deposition of related film on hardmetal surface, and provides guidance for future research.更多还原