【作者】 徐照英；

【导师】 冷永祥；

【作者基本信息】 西南交通大学 ， 材料学， 2013， 博士

【摘要】 类金刚石(DLC)薄膜由于具有高硬度和弹性模量、低摩擦系数、优异的耐磨损性和耐腐蚀性等优异性能,而成为具有广泛应用前景的保护膜及耐磨材料。多年的研究发现DLC薄膜中存在很大的残余应力,降低了薄膜与钛合金基体的结合强度,导致DLC薄膜在使用过程中的早期失效,限制了它的工业应用。多层薄膜是由不同材料相互交替沉积而成的组分或结构交替变化的薄膜材料,由于它具有大量的界面,通常会增加材料的韧性,阻碍裂纹的扩展,与相应的单层薄膜相比,多层薄膜的残余应力较低,且耐磨性能及耐蚀性能好,具有广泛的应用前景。因此,基于DLC薄膜急需解决的问题和实际应用的需要,设计了软硬交替DLC多层薄膜体系,其中软层将起到剪切带的作用,以缓解膜层中的内应力和界面应力。本文采用磁过滤阴极真空弧源(FCVA)沉积技术在Ti6A14V合金及Si(100)表面制备了一系列不同调制参数的软硬交替DLC多层薄膜和TiC/DLC多层薄膜,以减小或控制DLC薄膜中的残余应力、提高硬度和增强钛合金的摩擦学性能。本文系统研究了调制周期和调制比对软硬交替DLC多层薄膜和TiC/DLC多层薄膜的形貌、残余应力、成分、结构、机械性能和摩擦学性能的影响。同时采用有限元软件(Ansys)对软硬交替DLC多层薄膜的残余应力进行了模拟。为使基体与膜层之间形成良好的过渡,进一步增强膜基结合力,本文还研究了Ti/TiC梯度过渡层对DLC多层薄膜性能的影响。全文主要结果如下：(1)采用FCVA技术在钛合金表面成功的制备出了结构致密、低残余应力、高硬度和优异耐磨性能的软硬交替DLC多层薄膜和TiC/DLC多层薄膜。(2)使用FCVA技术制备的软硬交替DLC多层薄膜,在调制周期固定为140nm时,薄膜中sp3键的含量随调制比(硬DLC膜层与软DLC膜层厚度之比)的增大而增加；在调制比固定为1：1时,sp3键的含量随调制周期的减小而减小。DLC多层薄膜的残余应力均小于单层硬DLC薄膜,同时其机械性能均优于单层DLC薄膜。调制周期为140nm、调制比为1：1的软硬交替DLC多层薄膜具有最优异的耐磨损性能。(3)采用有限元方法分析了FCVA系统制备的DLC薄膜残余应力,有限元分析结果与实验分析结果具有较好的一致性。有限元分析表明,DLC薄膜的脱落从外侧起源是由于剪切应力和第一主应力在膜外侧边缘处具有最大的拉应力；不同调制周期DLC多层薄膜的残余应力大小对其力学性能有较大的影响。调制周期为280nm的DLC多层薄膜膜基界面上具有最大的剪切拉应力,因此膜基结合力较差；调制周期为140nm的DLC多层薄膜具有最优异的耐磨损性能主要是由于膜内拉应力最小和相对较好的膜基结合力。(4)制备偏压和乙炔分压对TiC薄膜的结构和力学性能均有明显的影响。利用XPS和XRD对膜的成分及结构分析中发现,在TiC薄膜中,碳除了和钛结合生成TiC相外,主要以氢化a-C：H非晶碳相形式存在；随着沉积乙炔分压的增加,膜中的钛含量降低,而薄膜中的a-C：H相的相对含量随之增加；随着钛含量的降低,硬度先增加而后逐渐减小。TiC薄膜的残余应力均为压应力,在基体偏压为AC1000V(20KHz,50%)、乙炔气压为0.15Pa时,TiC薄膜具有最小残余压应力4.17GPa。钛合金表面Ti/TiC梯度过渡层的引入,提高了DLC多层薄膜的硬度和膜基结合力,进一步提高了钛合金的耐磨损性能。(5)采用FCVA技术制备的TiC/DLC多层薄膜,通过TEM表征显示出清晰的多层膜调制结构。Raman光谱分析表明TiC/DLC多层薄膜中sp3键含量随调制比(TiC膜层与DLC膜层厚度之比)的增大逐渐减少。在调制周期固定为106nm时,残余应力随调制比的增大而减小,调制比为4：1的多层膜残余压应力达到最小值(4.81GPa),同时具有最高的膜基结合强度。在调制比固定为1：1时,残余应力随调制周期的减小而减小,调制周期为80nm的多层残余应力最小、薄膜硬度和结合强度最高。调制比为1：1、调制周期为106nm的TiC/DLC多层薄膜具有最优异的耐磨损性能。TiC/DLC多层薄膜的残余应力,膜基结合力,以及摩擦性能都明显优于单层DLC薄膜。本文的研究结果表明,采用FCVA技术制备的软硬交替DLC多层薄膜和TiC/DLC多层薄膜能有效的降低DLC薄膜在制备过程中产生的残余应力和增加膜基结合力,同时保持DLC薄膜高的硬度和优异的耐磨损性能。更多还原

【Abstract】 Diamond-like carbon (DLC) films have great potential as protective coating and wear resistance material because of their unusual and promising properties such as high hardness, high elastic modulus, low friction coefficient, excellent wear resistance, good corrosion resistance and excellent chemical stability etc. However, the major drawback of DLC film is its high internal compressive stress. And this high stress frequently leads to debonding, cracking, or delamination of the film from the Ti6A14V alloy substrate, which limits the DLC film practical application. Multilayer films can be structured by deposited with several different materials by order. The multilayer films have wide application prospect since their have a lot of interface, usually will increase the toughness of materials and prevent crack propagation. The multilayer films have lower compressive stress, better wear resistance and corrosion resistant than the monolithic film. Considering the urgent problems of DLC film and industrial appilcations, we designed soft/hard DLC multilayer system, in which soft layer operate as shearing bonds to release the internal stress and interface stress.This paper synthesized a series of soft/hard DLC multilayer films and TiC/DLC multilayer films with different modulation parameters on Si(100) and Ti6A14V alloy by filtered cathodic vacuum arc(FCVA)technology in order to solve the problem of the internal compressive stress in the DLC film, increase hardness and enhance tribological properties of titanium alloy. The effect of modulation periods and modulation ratios on the micro structure and properties of the DLC multilayer films including surface morphology, residual stress, composition, structure, mechanical properties and wear resistance were studied. ANSYS finite element software was used to simulate the residual stress generation during filtered cathodic vacuum arc deposition in DLC multilayer films. In order to make a good transition between the film and further increase the adhesion strength. The effect of Ti/TiC gradient transition layer on mechanical proptery and tribological proptery of DLC multilayer films were studied. The main results of this paper are as follows:(1) The soft/hard DLC multilayer films and TiC/DLC multilayer films with compact structure, low residual stress, high hardness and wear resistance have been fabricated on Ti64alloys and Si (100) wafer using FCVA technique.(2) The soft/hard DLC multilayer films have synthesized by FCVA technique. Within constant modulation period of140nm, the sp3content increases with modulation ratios (thickness ratios, hard DLC:soft DLC) increasing. Within constant modulation ratio of1:1, the sp3content decreases with modulation periods decreasing. The soft/hard DLC multilayer films have lower compressive stress than the monolithic hard DLC layers, and the mechanical properties are superior to monolithic films. The soft/hard DLC multilayer film with modulation ratio of1:1and modulation period of140nm shows the most excellent wear resistance.(3) The finite element model (FEM) with an axial symmetric was used to simulate residual stress in DLC film.The finite element simulation results of residual stress are in reasonably good agreement with experimental results. Finite element calculation results show that the DLC films delamination from the outside origin is due to the largest shear stress and the first principal stress. The residual stress strongly affects the mechanical properties of multilayer DLC films with different modulation periods. The DLC multilayer film with modulation period of280nm has the bad adhesion strength owing to high residual stress and shear stress. The DLC multilayer film with modulation period of140nm has the most excellent wear resistance owing to better adhesion strength and the minimum tensile stress.(4) The bias voltage and acetylene partial pressure strongly affects the microstructure and mechanical properties of the TiC films. The composition and structure were measured by XPS and XRD.The carbon exist as hydrogenate amorphous phase (a-C:H) besides combine with the titanium and format TiC phase.The titanium atomic content decrease with increase of acetylene partial pressure, and the a-C:H phase concentration increase with decrease of titanium content in films. Hardness of the TiC films increases firstly and then decreases with decreasing titanium content. The TiC film with substrate bias of AC1000V (20KHz,50%) and acetylene partial pressure of0.15Pa has the minimum compressive stress4.17GPa.With the introduction of Ti/TiC gradient transition layer, the hardness and adhesion strength of DLC multilayer film on Ti6A14V alloys can be increased, and the wear resistance of Ti6A14V alloys can be further improved.(5) The TiC/DLC multilayer films have synthesized by FCVA technique. The multilayered modulation structure and clear interface were confirmed by TEM. Raman’s spectra of TiC/DLC multilayer films indicate that the sp3content decreases with modulation ratios (thickness ratios, TiC:DLC) increasing. Within constant modulation period of106nm, the residual stress decreases with increasing of modulation ratio. The TiC/DLC multilayer film with modulation ratio of4:1has the best adhesion strength and the lowest compressive stress (4.81GPa). Within constant modulation ratio of1:1, with modulation period decreasing, the residual stress decreases. The TiC/DLC multilayer film with modulation period of80nm has the highest hardness、best adhesion strength and the lowest compressive stress. With the optimal modulation ratio of1:1and modulation period of106nm, the TiC/DLC multilayer film has the most excellent wear resistance. The TiC/DLC multilayer films have lower compressive stress than the monolithic hard DLC film; the multilayer films exhibited better adhesion strength and wear resistance than monolithic DLC film.All results above demonstrated that soft/hard DLC multilayer films and TiC/DLC multilayer films prepared by filtered cathodic vacuum arc technology can effectively reduce the residual stress of DLC film and increase adhesion strength, while keeping the high hardness and wear resistance of DLC film.更多还原