【作者】 张爽；

【导师】 钱林茂；

【作者基本信息】 西南交通大学 ， 机械设计及理论， 2008， 硕士

【摘要】 氮化铬(CrN_x)薄膜和非晶态氮化碳(a-CN_x)薄膜具有良好的机械性能,被广泛应用作切削刀具、生物医学工程以及微机电系统(MEMS)等领域的耐磨涂层。另外,由于温度变化和机械振动,纳动普遍存在于MEMS中,并已成为导致MEMS失效的重要损伤形式之一。因此,研究CrN_x薄膜和a-CN_x薄膜的纳动特性具有十分重要的意义。本文首先利用纳米压痕仪,系统研究了CrN_x薄膜及a-CN_x薄膜径向纳动力～位移曲线的动态变化过程,进而利用扫描电子显微镜(SEM)、激光共焦显微镜(LCSM)等设备对纳动损伤进行微观分析,深入研究了两种薄膜的纳动损伤特性和机理。在此基础上,初步探讨了膜厚与压头曲率半径对薄膜纳动性能的影响。通过研究,本文获得主要结论如下:1.在纳动过程中,CrN_x薄膜能够提高40Cr基体的抗压能力,增大其接触刚度,降低其残余压痕深度,减少其在纳动循环过程中的能量耗散。40Cr基体的纳动损伤主要表现为压痕边缘的塑性堆积,而CrN_x薄膜的纳动损伤主要表现为环向裂纹和径向裂纹的萌生与扩展。2.随着循环次数的增加,Si(100)基体上的a-CN_x薄膜的损伤可分为压头周围薄膜发生弯曲、环向裂纹形成和薄膜从基体上剥落三个阶段。3.材料的接触刚度对其变形和损伤非常敏感,可以从接触刚度随纳动循环次数的变化曲线来判断超薄薄膜的纳动损伤过程。4.薄膜与基体的弹性模量越接近,纳动过程中薄膜与基体的变形协调能力越好,膜/基体系的抗纳动损伤能力越强。因此,可利用改变薄膜的弹性模量的方法来提高MEMS的使用寿命。5.膜厚对薄膜纳动损伤的影响比较复杂,涉及压头的压入应力、薄膜沉积过程中的残余应力以及薄膜本身的弹塑性变形等。随着压头曲率半径的减小,相同载荷下接触区的最大压入应力急剧增加,使得薄膜纳动损伤的临界载荷不断降低。更多还原

【Abstract】 Due to their excellent mechanical properties,chromium nitride(CrN_x)and amorphous carbon nitride(a-CN_x)films have been widely employed as protective hard coatings in the areas of cutting tools,biomedical enginerring and microelectromechanical systems(MEMS).On the other hand,because of the variation of temperature and mechanical vibration,nanofretting widely exists in MEMS and has become a key tribological problem of concern.Therefore,it is important to understand the nanofretting properties of the CrN_x and a-CN_x films.With a nanoindenter,the nanofretting behaviors of CrN_x film and a-CN_x film were studied by using a spherical diamond indenter under various applied normal load.The nanofretting damage of the films was analyzed by scanning electron microscopy(SEM)and laser confocal scanning microscopy(LCSM).Finally,the effects of film thickness and curvature radius of indenter on the nanofretting damage of film were also discussed.The main conclusions of the research can be summaried as following:1.The CrN_x film can effectively improve the anti-pressure ability of 40Cr substrate.Under the same conditions,the CrN_x film exhibited larger contact stiffness,but smaller residual indentation depth and less energy dissipation than 40Cr substrate.The radial nanofretting damage in 40Cr was mainly identified as the pileup of the plastic deformation around indents.However, the radial nanofretting damage in CrN_x film was characterized as the initiation and propagation of the ring and radial cracks,which were raised from the radial and hoop tensile stress on the interface of CrN_x film and substrate.2.The nanofatigue damage of the a-CN_x film on Si(100)substrate was found to start from the buckling of the film,follow by the initiation and propagation of the ring-like crack at the edge of the buckled film,and finish at the detachment of the film from the substrate with the increase in the number of the nanofretting cycle.3.The contact stiffness is very sensitive to the deformation and damage of the film.Therefore,an indentation method could be developed to characterize the nanofatigue behavior of ultrathin films from the variation of their contact stiffness.4.Film-substrate system will exhibit better deformation compatibility and in turn better unti-nanofretting ability when the elastic modulus of the film is similar as that of the substrate.Therefore,it is possible to improve the service life of the MEMS by adjusting the elastic modulus of films.5.The film thickness effect on the nanofretting behaviors of the films was very complicated,which may be affected by the indentation stress of indenter,the residual stresses induced in film by the deposition process and the deformation state of the film.With the decrese in the curvature radius of indenter,the maximum contact stress will increase sharply at the same indentation force,which leads to the decrease in the critical load of nanofretting damage.更多还原